| SUDOERS(5) | File Formats Manual | SUDOERS(5) |
sudoers — default
sudo security policy plugin
The sudoers policy plugin determines a
user's sudo privileges. It is the default
sudo policy plugin. The policy is driven by the
/etc/sudoers file or, optionally, in LDAP. The
policy format is described in detail in the
SUDOERS FILE FORMAT section.
For information on storing sudoers policy
information in LDAP, see
sudoers.ldap(5).
sudo consults the
sudo.conf(5) file to determine which
plugins to load. If no sudo.conf(5)
file is present, or if it contains no Plugin lines,
sudoers will be used for auditing, policy decisions
and I/O logging. To explicitly configure
sudo.conf(5) to use the
sudoers plugin, the following configuration can be
used.
Plugin sudoers_audit sudoers.so Plugin sudoers_policy sudoers.so Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible
to specify optional arguments to the sudoers plugin
in the sudo.conf(5) file. Plugin
arguments, if any, should be listed after the path to the plugin (i.e.,
after sudoers.so). The arguments are only effective
for the plugin that opens (and parses) the sudoers
file.
For sudo version 1.9.1
and higher, this is the
sudoers_audit
plugin. For older versions, it is the
sudoers_policy
plugin. Multiple arguments may be specified, separated by white space. For
example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
sudoers
should attempt to recover from syntax errors in the
sudoers file. If set to
true
(the default), sudoers will try to recover from a
syntax error by discarding the portion of the line that contains the error
until the end of the line. A value of false will disable
error recovery. Prior to version 1.9.3, no error recovery was
performed.For more information on configuring sudo.conf(5), refer to its manual.
The sudoers security policy requires that
most users authenticate themselves before they can use
sudo. A password is not required if the invoking
user is root, if the target user is the same as the
invoking user, or if the policy has disabled authentication for the user or
command. Unlike su(1), when
sudoers requires authentication, it validates the
invoking user's credentials, not the target user's (or
root's) credentials. This can be
changed via the rootpw, targetpw and
runaspw flags, described later.
If a user who is not listed in the policy tries to run a command
via sudo, mail is sent to the proper authorities.
The address used for such mail is configurable via the
mailto Defaults entry (described later) and defaults to
root.
No mail will be sent if an unauthorized user tries to run
sudo with the -l or
-v option unless there is an authentication error
and either the mail_always or
mail_badpass flags are enabled. This allows users to
determine for themselves whether or not they are allowed to use
sudo. By default, all attempts to run
sudo (successful or not) are logged, regardless of
whether or not mail is sent.
If sudo is run by root
and the SUDO_USER environment variable is set, the
sudoers policy will use this value to determine who
the actual user is. This can be used by a user to log commands through sudo
even when a root shell has been invoked. It also allows
the -e option to remain useful even when invoked via
a sudo-run script or program. Note, however, that the
sudoers file lookup is still done for
root, not the user specified by
SUDO_USER.
sudoers uses per-user time stamp files for
credential caching. Once a user has been authenticated, a record is written
containing the user-ID that was used to authenticate, the terminal session
ID, the start time of the session leader (or parent process) and a time
stamp (using a monotonic clock if one is available). The user may then use
sudo without a password for a short period of time
(5 minutes unless overridden by the timestamp_timeout
option). By default, sudoers uses a separate record
for each terminal, which means that a user's login sessions are
authenticated separately. The timestamp_type option can be
used to select the type of time stamp record sudoers
will use.
By default, sudoers logs both successful
and unsuccessful attempts (as well as errors). The
log_allowed
and
log_denied
flags can be used to control this behavior. Messages can be logged to
syslog(3), a log file, or both. The
default is to log to syslog(3) but this
is configurable via the syslog and
logfile settings. See
EVENT LOGGING for a description of
the log file format.
sudoers is also capable of running a
command in a pseudo-terminal and logging input and/or output. The standard
input, standard output, and standard error can be logged even when not
associated with a terminal. For more information about I/O logging, see the
I/O LOGGING section.
Starting with version 1.9, the log_servers
setting may be used to send event and I/O log data to a remote server
running sudo_logsrvd or another service that
implements the protocol described by
sudo_logsrv.proto(5).
Since environment variables can influence program behavior,
sudoers provides a means to restrict which variables
from the user's environment are inherited by the command to be run. There
are two distinct ways sudoers can deal with
environment variables.
By default, the env_reset flag is enabled. This
causes commands to be executed with a new, minimal environment. On AIX (and
Linux systems without PAM), the environment is initialized with the contents
of the /etc/environment file. The
HOME, MAIL,
SHELL, LOGNAME and
USER environment variables are initialized based on
the target user and the SUDO_* variables are set
based on the invoking user. Additional variables, such as
DISPLAY, PATH and
TERM, are preserved from the invoking user's
environment if permitted by the env_check, or
env_keep options. A few environment variables are treated
specially. If the PATH and
TERM variables are not preserved from the user's
environment, they will be set to default values. The
LOGNAME and USER are handled
as a single entity. If one of them is preserved (or removed) from the user's
environment, the other will be as well. If LOGNAME
and USER are to be preserved but only one of them is
present in the user's environment, the other will be set to the same value.
This avoids an inconsistent environment where one of the variables
describing the user name is set to the invoking user and one is set to the
target user. Environment variables with a value beginning with
‘()’ are removed unless both the name
and value parts are matched by env_keep or
env_check, as they may be interpreted as functions by the
bash shell. Prior to version 1.8.11, such variables were
always removed.
If, however, the env_reset flag is disabled, any
variables not explicitly denied by the env_check and
env_delete options are allowed and their values are
inherited from the invoking process. Prior to version 1.8.21, environment
variables with a value beginning with
‘()’ were always removed. Beginning
with version 1.8.21, a pattern in env_delete is used to
match bash shell functions instead. Since it is not
possible to block all potentially dangerous environment variables, use of
the default env_reset behavior is encouraged.
Environment variables specified by env_check,
env_delete, or env_keep may include one
or more ‘*’ characters which will
match zero or more characters. No other wildcard characters are
supported.
By default, environment variables are matched by name. However, if
the pattern includes an equal sign
(‘=’), both the variables name and
value must match. For example, a bash shell function could
be matched as follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the ‘=()*’ suffix,
this would not match, as bash shell functions are not
preserved by default.
The complete list of environment variables that are preserved or
removed, as modified by global Defaults parameters in
sudoers, is displayed when sudo is
run by root with the -V option.
The list of environment variables to remove varies based on the operating
system sudo is running on.
Other settings may influence the command environment:
sudoers options such as
always_set_home,
secure_path, set_logname,
set_home,
and setenv.SETENV and
NOSETENV. Note that SETENV
is implied if the command matched is ALL.sudo options, such as -E
and -i.On systems that support PAM where the
pam_env module is
enabled for sudo, variables in the PAM environment
may be merged in to the environment. If a variable in the PAM environment is
already present in the user's environment, the value will only be overridden
if the variable was not preserved by sudoers. When
env_reset is enabled, variables preserved from the
invoking user's environment by the env_keep list take
precedence over those in the PAM environment. When
env_reset is disabled, variables present the invoking
user's environment take precedence over those in the PAM environment unless
they match a pattern in the env_delete list.
The dynamic linker on most operating systems will remove variables
that can control dynamic linking from the environment of set-user-ID
executables, including sudo. Depending on the
operating system this may include _RLD*,
DYLD_*, LD_*,
LDR_*, LIBPATH,
SHLIB_PATH, and others. These type of variables are
removed from the environment before sudo even begins
execution and, as such, it is not possible for sudo
to preserve them.
As a special case, if the -i option
(initial login) is specified, sudoers will
initialize the environment regardless of the value of
env_reset. The DISPLAY,
PATH and TERM variables
remain unchanged; HOME,
MAIL, SHELL,
USER, and LOGNAME are set
based on the target user. On AIX (and Linux systems without PAM), the
contents of /etc/environment are also included. All
other environment variables are removed unless permitted by
env_keep or env_check, described
above.
Finally, the restricted_env_file and env_file files are applied, if present. The variables in restricted_env_file are applied first and are subject to the same restrictions as the invoking user's environment, as detailed above. The variables in env_file are applied last and are not subject to these restrictions. In both cases, variables present in the files will only be set to their specified values if they would not conflict with an existing environment variable.
The sudoers file is composed of two types of entries: aliases (basically variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly simple, and the definitions below are annotated.
By default, sudoers uses the operating
system's native method of setting resource limits for the target user. On
Linux systems, resource limits are usually set by the
pam_limits.so PAM module. On some BSD systems, the
/etc/login.conf file specifies resource limits for
the user. On AIX systems, resource limits are configured in the
/etc/security/limits file. If there is no system
mechanism to set per-user resource limits, the command will run with the
same limits as the invoking user. The one exception to this is the core dump
file size, which is set by sudoers to 0 by default.
Disabling core dumps by default makes it possible to avoid potential
security problems where the core file is treated as trusted input.
Resource limits may also be set in the
sudoers file itself, in which case they override those set
by the system. See the
rlimit_as,
rlimit_core,
rlimit_cpu,
rlimit_data,
rlimit_fsize,
rlimit_locks,
rlimit_memlock,
rlimit_nofile,
rlimit_nproc,
rlimit_rss,
rlimit_stack
options described below. Resource limits in sudoers
may be specified in one of the following formats:
\’). The special value
“infinity” may be used in place of either value.sudo was invoked for systems that don't support
per-user limits.For example, to restore the historic core dump file size behavior, a line like the following may be used.
Defaults
rlimit_core=defaultResource limits in sudoers are only
supported by version 1.8.7 or higher.
EBNF is a concise and exact way of describing the grammar of a language. Each EBNF definition is made up of production rules. For example:
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for the language. EBNF also contains the following operators, which many readers will recognize from regular expressions. Do not, however, confuse them with “wildcard” characters, which have different meanings.
Parentheses may be used to group symbols together. For clarity, we will use single quotes ('') to designate what is a verbatim character string (as opposed to a symbol name).
There are four kinds of aliases: User_Alias,
Runas_Alias, Host_Alias and
Cmnd_Alias. Beginning with sudo
1.9.0,
Cmd_Alias
may be used in place of Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where
Alias_Type is
one of User_Alias, Runas_Alias,
Host_Alias, or Cmnd_Alias. A
NAME is a string of uppercase letters, numbers, and
underscore characters (‘_’). A
NAME
must start
with an uppercase letter. It is possible to put several alias definitions of
the same type on a single line, joined by a colon
(‘:’). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to use the same name for aliases of different types, but this is not recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user
names, user-IDs (prefixed with ‘#’),
system group names and IDs (prefixed with
‘%’ and
‘%#’ respectively), netgroups
(prefixed with ‘+’), non-Unix group
names and IDs (prefixed with ‘%:’ and
‘%:#’ respectively), and
User_Aliases. Each list item may be prefixed with zero or
more ‘!’ operators. An odd number of
‘!’ operators negate the value of the
item; an even number just cancel each other out. User netgroups are matched
using the user and domain members only; the host member is not used when
matching.
A user name, user-ID, group, group-ID, netgroup, nonunix_group or nonunix_gid may be enclosed in double quotes to avoid the need for escaping special characters. Alternately, special characters may be specified in escaped hex mode, e.g., \x20 for space. When using double quotes, any prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying group provider plugin. For instance, the QAS AD plugin supports the following formats:
See GROUP PROVIDER PLUGINS for more information.
Quotes around group names are optional. Unquoted strings must use
a backslash (‘\’) to escape spaces and
special characters. See
Other
special characters and reserved words for a list of characters that need
to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias |
'!'* ALL
A Runas_List is similar to a User_List except that instead of User_Aliases it can contain Runas_Aliases. User names and groups are matched as strings. In other words, two users (groups) with the same user (group) ID are considered to be distinct. If you wish to match all user names with the same user-ID (e.g., root and toor), you can use a user-ID instead of a name (#0 in the example given). The user-ID or group-ID specified in a Runas_Member need not be listed in the password or group database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias |
'!'* ALL
A Host_List is made up of one or more host
names, IP addresses, network numbers, netgroups (prefixed with
‘+’), and other aliases. Again, the
value of an item may be negated with the
‘!’ operator. Host netgroups are
matched using the host (both qualified and unqualified) and domain members
only; the user member is not used when matching. If you specify a network
number without a netmask, sudo will query each of
the local host's network interfaces and, if the network number corresponds
to one of the hosts's network interfaces, will use the netmask of that
interface. The netmask may be specified either in standard IP address
notation (e.g., 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation
(number of bits, e.g., 24 or 64). A host name may include shell-style
wildcards (see the Wildcards section
below), but unless the hostname command on your machine
returns the fully qualified host name, you'll need to use the
fqdn flag for wildcards to be useful.
sudo only inspects actual network interfaces; this
means that IP address 127.0.0.1 (localhost) will never match. Also, the host
name “localhost” will only match if that is the actual host
name, which is usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= regex |
file name
command ::= command name |
command name args |
command name regex |
command name '""' |
ALL
Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"
List_Spec ::= "list"
Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more
commands, directories, or aliases. A command is a fully qualified file name,
which may include shell-style wildcards (see the
Wildcards section below), or a regular
expression that starts with ‘^’ and
ends with ‘$’ (see the
Regular expressions section
below). A directory is a fully qualified path name ending in a
‘/’. When you specify a directory in a
Cmnd_List, the user will be able to run any file within
that directory (but not in any sub-directories therein). If no command line
arguments are specified, the user may run the command with any arguments
they choose. Command line arguments can include wildcards or be a regular
expression that starts with ‘^’ and
ends with ‘$’. If the command line
arguments consist of ‘""’,
the command may only be run with
no arguments.
If a Cmnd has associated command line arguments,
the arguments in the Cmnd must match those given by the
user on the command line. If the arguments in a Cmnd begin
with the ‘^’ character, they will be
interpreted as a regular expression and matched accordingly. Otherwise,
shell-style wildcards are used when matching. Unless a regular expression is
specified, the following characters must be escaped with a
‘\’ if they are used in command
arguments: ‘,’,
‘:’,
‘=’,
‘\’. To prevent arguments in a
Cmnd that begin with a
‘^’ character from being interpreted
as a regular expression, the ‘^’ must
be escaped with a ‘\’.
There are two commands built into sudo
itself: “list” and “sudoedit”. Unlike other
commands, these two must be specified in the sudoers file
without a leading path.
The “list” built-in can be used to permit a user to
list another user's privileges with sudo's
-U option. For example, “sudo -l -U
otheruser”. A user with the “list” privilege is able to
list another user's privileges even if they don't have permission to run
commands as that user. By default, only root or a user with the ability to
run any command as either root or the specified user
on the current host may use the -U option. No
command line arguments may be specified with the “list”
built-in.
The “sudoedit” built-in is used to permit a user to
run sudo with the -e option
(or as sudoedit). It may take command line arguments
just as a normal command does. Unlike other commands,
“sudoedit” is built into sudo itself
and must be specified in the sudoers file
without a leading path. If a leading path is present, for
example /usr/bin/sudoedit, the path name will be
silently converted to “sudoedit”. A fully-qualified path for
sudoedit is treated as an error by
visudo.
A command may be preceded by a Digest_List, a comma-separated list of one or more Digest_Spec entries. If a Digest_List is present, the command will only match successfully if it can be verified using one of the SHA-2 digests in the list. Starting with version 1.9.0, the ALL reserved word can be used in conjunction with a Digest_List. The following digest formats are supported: sha224, sha256, sha384, and sha512. The string may be specified in either hex or base64 format (base64 is more compact). There are several utilities capable of generating SHA-2 digests in hex format such as openssl, shasum, sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64 EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself
(directly or via a sudo command), it may be possible
for the user to replace the command after the digest check has been
performed but before the command is executed. A similar race condition
exists on systems that lack the
fexecve(2) system call when the
directory in which the command is located is writable by the user. See the
description of the fdexec setting for more information on
how sudo executes commands that have an associated
digest.
Command digests are only supported by version 1.8.7 or higher.
Certain configuration options may be changed from their default values at run-time via one or more Default_Entry lines. These may affect all users on any host (‘Defaults’), all users on a specific host (‘Defaults@host’), a specific user (‘Defaults:user’), a specific command (‘Defaults!cmnd’), or commands being run as a specific user (‘Defaults>runasuser’).
White space is not permitted between ‘Defaults’ and
the ‘@’,
‘:’,
‘!’, or
‘>’ characters. While a
comma-separated list may be used in place of a single value after the
‘@’,
‘:’,
‘!’, or
‘>’ character, using an alias
instead of a list is often improve readability. Per-command entries may not
include command line arguments. If you need to specify arguments, define a
Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults@' Host_List |
'Defaults:' User_List |
'Defaults!' Cmnd_List |
'Defaults>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be
flags,
integer
values,
strings,
or
lists.
Flags are implicitly boolean and can be turned off via the
‘!’ operator. Some integer, string and
list parameters may also be used in a boolean context to disable them.
Values may be enclosed in double quotes ("") when they contain
multiple words. Special characters may be escaped with a backslash
(‘\’).
To include a literal backslash character in a command line
argument you must escape the backslash twice. For example, to match
‘\n’ as part of a command line
argument, you must use ‘\\\\n’ in the
sudoers file. This is due to there being two levels of
escaping, one in the sudoers parser itself and another
when command line arguments are matched by the
fnmatch(3) or
regexec(3) function.
Lists have two additional assignment operators,
‘+=’ and
‘-=’. These operators are used to add
to and delete from a list respectively. It is not an error to use the
‘-=’ operator to remove an element
that does not exist in a list.
Defaults entries are parsed in the following order: global, host, user, and runas Defaults first, then command defaults. If there are multiple Defaults settings of the same type, the last matching setting is used. The following Defaults settings are parsed before all others since they may affect subsequent entries: fqdn, group_plugin, runas_default, sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' |
'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' |
'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' |
'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' |
'NOSETENV')
A user specification determines which commands a user may run (and as what user) on specified hosts. By default, commands are run as root (unless runas_default has been set to a different value) but this can also be changed on a per-command basis.
The basic structure of a user specification is “who where = (as_whom) what”. Let's break that down into its constituent parts:
A Runas_Spec determines the user and/or the
group that a command may be run as. A fully-specified
Runas_Spec consists of two Runas_Lists
(as defined above) separated by a colon
(‘:’) and enclosed in a set of
parentheses. The first Runas_List indicates which users
the command may be run as via the -u option. The
second defines a list of groups that may be specified via the
-g option (in addition to any of the target user's
groups). If both Runas_Lists are specified, the command
may be run with any combination of users and groups listed in their
respective Runas_Lists. If only the first is specified,
the command may be run as any user in the list and, optionally, with any
group the target user belongs to. If the first Runas_List
is empty but the second is specified, the command may be run as the invoking
user with the group set to any listed in the Runas_List.
If both Runas_Lists are empty, the command may only be run
as the invoking user and the group, if specified, must be one that the
invoking user is a member of. If no Runas_Spec is
specified, the command may only be run as the
runas_default user (root by default) and
the group, if specified, must be one that the
runas_default user is a member of.
A Runas_Spec sets the default for the commands that follow it. What this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host boulder—but only as operator. For example:
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\ /usr/bin/lprm
While the group portion of the Runas_Spec permits the user to run as command with that group, it does not force the user to do so. If no group is specified on the command line, the command will run with the group listed in the target user's password database entry. The following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls $ sudo -u operator -g operator /bin/ls $ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\ /usr/local/bin/minicom
In this example only the group will be set, the command still runs as user tcm. For example:
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a
Runas_Spec, in which case the user may select any
combination of users and groups via the -u and
-g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally setting the group to operator or system.
A Cmnd may have zero or more options associated with it. Options may consist of start and/or end dates and command timeouts. Once an option is set for a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit that option unless it is overridden by another option. Option names are reserved words in sudoers. This means that none of the valid option names (see below) can be used when declaring an alias.
sudoers rules can be specified with a
start and end date via the NOTBEFORE and
NOTAFTER settings. The time stamp must be specified
in “Generalized Time” as defined by RFC 4517. The format is
effectively ‘yyyymmddHHMMSSZ’ where
the minutes and seconds are optional. The
‘Z’ suffix indicates that the time
stamp is in Coordinated Universal Time (UTC). It is also possible to specify
a timezone offset from UTC in hours and minutes instead of a
‘Z’. For example,
‘-0500’ would correspond to Eastern
Standard time in the US. As an extension, if no
‘Z’ or timezone offset is specified,
local time will be used.
The following are all valid time stamps:
20170214083000Z 2017021408Z 20160315220000-0500 20151201235900
A command may have a timeout associated with it. If the timeout
expires before the command has exited, the command will be terminated. The
timeout may be specified in combinations of days, hours, minutes, and
seconds with a single-letter case-insensitive suffix that indicates the unit
of time. For example, a timeout of 7 days, 8 hours, 30 minutes, and 10
seconds would be written as
‘7d8h30m10s’. If a number is specified
without a unit, seconds are assumed. Any of the days, minutes, hours, or
seconds may be omitted. The order must be from largest to smallest unit and
a unit may not be specified more than once.
The following are all
valid timeout
values: ‘7d8h30m10s’,
‘14d’,
‘8h30m’,
‘600s’,
‘3600’. The following are
invalid
timeout values: ‘12m2w1d’,
‘30s10m4h’,
‘1d2d3h’.
This setting is only supported by version 1.8.20 or higher.
The working directory that the command will be run in can be
specified using the CWD setting. The
directory must be a fully-qualified path name
beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that
the user may specify the working directory by running
sudo with the -D option. By
default, commands are run from the invoking user's current working
directory, unless the -i option is given. Path names
of the form ~user/path/name are interpreted as being
relative to the named user's home directory. If the user name is omitted,
the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
The root directory that the command will be run in can be
specified using the CHROOT setting. The
directory must be a fully-qualified path name
beginning with a ‘/’ or ‘~’ character, or the
special value “*”. A value of “*” indicates that
the user may specify the root directory by running
sudo with the -R option.
This setting can be used to run the command in a
chroot(2) “sandbox” similar
to the chroot(8) utility. Path names of
the form ~user/path/name are interpreted as being
relative to the named user's home directory. If the user name is omitted,
the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
A command may have zero or more tags associated with it. The
following tag values are supported: EXEC,
NOEXEC, FOLLOW,
NOFOLLOW, LOG_INPUT,
NOLOG_INPUT, LOG_OUTPUT,
NOLOG_OUTPUT, MAIL,
NOMAIL, INTERCEPT,
NOINTERCEPT, PASSWD,
NOPASSWD, SETENV, and
NOSETENV. Once a tag is set on a
Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit the tag unless it is overridden by
the opposite tag (in other words, PASSWD overrides
NOPASSWD and NOEXEC
overrides EXEC).
EXEC
and NOEXECIf sudo has been compiled with
noexec support and the underlying operating system
supports it, the NOEXEC tag can be used to
prevent a dynamically-linked executable from running further commands
itself.
In the following example, user aaron may run /usr/bin/more and /usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the
Preventing shell
escapes section below for more details on how
NOEXEC works and whether or not it will work on
your system.
FOLLOW
and NOFOLLOWStarting with version 1.8.15, sudoedit
will not open a file that is a symbolic link unless the
sudoedit_follow flag is enabled. The
FOLLOW and NOFOLLOW tags
override the value of sudoedit_follow and can be used
to permit (or deny) the editing of symbolic links on a per-command
basis. These tags are only effective for the sudoedit
command and are ignored for all other commands.
LOG_INPUT
and NOLOG_INPUTThese tags override the value of the log_input flag on a per-command basis. For more information, see I/O LOGGING.
LOG_OUTPUT
and NOLOG_OUTPUTThese tags override the value of the log_output flag on a per-command basis. For more information, see I/O LOGGING.
MAIL
and NOMAILThese tags provide fine-grained control over whether mail will
be sent when a user runs a command by overriding the value of the
mail_all_cmnds flag on a per-command basis. They have
no effect when sudo is run with the
-l or -v options. A
NOMAIL tag will also override the
mail_always and mail_no_perms
options. For more information, see the descriptions of
mail_all_cmnds, mail_always, and
mail_no_perms in the
SUDOERS OPTIONS section
below.
PASSWD
and NOPASSWDBy default, sudo requires that a user
authenticate before running a command. This behavior can be modified via
the NOPASSWD tag. Like a
Runas_Spec, the NOPASSWD tag
sets a default for the commands that follow it in the
Cmnd_Spec_List. Conversely, the
PASSWD tag can be used to reverse things. For
example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm as root on the machine “rushmore” without authenticating himself. If we only want ray to be able to run /bin/kill without a password the entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has
no effect on users who are in the group specified by the
exempt_group setting.
By default, if the
NOPASSWD tag is applied to any of a user's
entries for the current host, the user will be able to run
‘sudo -l’ without a password.
Additionally, a user may only run ‘sudo
-v’ without a password if all of the user's entries for
the current host have the NOPASSWD tag. This
behavior may be overridden via the
verifypw and
listpw
options.
SETENV
and NOSETENVThese tags override the value of the setenv
flag on a per-command basis. If SETENV has been
set for a command, the user may disable the env_reset
flag from the command line via the -E option.
Additionally, environment variables set on the command line are not
subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such,
only trusted users should be allowed to set variables in this manner. If
the command matched is ALL, the
SETENV tag is implied for that command; this
default may be overridden by use of the NOSETENV
tag.
INTERCEPT
and NOINTERCEPTIf sudo has been compiled with
intercept support and the underlying operating system
supports it, the INTERCEPT tag can be used to
cause programs spawned by a command to be validated against
sudoers and logged just like they would be if run
through sudo directly. This is useful in
conjunction with commands that allow shell escapes such as editors,
shells, and paginators. There is additional overhead due to the policy
check that may add latency when running commands such as shell scripts
that execute a large number of sub-commands. For interactive commands,
such as a shell or editor, the overhead is not usually noticeable.
In the following example, user chuck may run any command on the machine “research” in intercept mode.
chuck research = INTERCEPT: ALL
See the
Preventing shell
escapes section below for more details on how
INTERCEPT works and whether or not it will work
on your system.
sudo allows shell-style
wildcards (aka meta or glob characters) to be used in host
names, path names, and command line arguments in the
sudoers file. Wildcard matching is done via the
glob(3) and
fnmatch(3) functions as specified by
IEEE Std 1003.1 (“POSIX.1”).
*’,
‘?’,
‘[’, and
‘]’.Character classes may be used if your system's
glob(3) and
fnmatch(3) functions support them.
However, because the ‘:’ character has
special meaning in sudoers, it must be escaped. For
example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
A forward slash (‘/’) will
not be matched by wildcards used in the file name portion
of the command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get matched by wildcards since command line arguments may contain arbitrary strings and not just path names.
The following exceptions apply to the above rules:
""’
is the only command line argument in the sudoers file
entry it means that command is not allowed to be run with
any arguments./’) will not be matched by a
wildcard.Starting with version 1.9.10, it is possible to use regular
expressions for path names and command line arguments. Regular expressions
are more expressive than shell-style wildcards and are
usually safer because they provide a greater degree of control when
matching. The type of regular expressions supported by
sudoers are POSIX extended regular expressions,
similar to those used by the egrep(1)
utility. They are usually documented in the
regex(7) or
re_format(7) manual, depending on the
system. As an extension, if the regular expression begins with
“(?i)”, it will be matched in a case-insensitive manner.
In sudoers, regular expressions must start with
a ‘^’ character and end with a
‘$’. This makes it explicit what is,
or is not, a regular expression. Either the path name, the command line
arguments or both may be regular expressions. Because the path name and
arguments are matched separately, it is even possible to use wildcards for
the path name and regular expressions for the arguments. It is not possible
to use a single regular expression to match both the command and its
arguments. Regular expressions in sudoers are limited to
1024 characters.
There is no need to escape sudoers special
characters in a regular expression other than the pound sign
(‘#’).
In the following example, user john can run the passwd(1) command as root on any host but is not allowed to change root's password. This kind of rule is impossible to express safely using wildcards.
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd root
It is also possible to use a regular expression in conjunction
with sudoedit rules. The following rule would give
user bob the ability to edit the /etc/motd,
/etc/issue, and /etc/hosts
files only.
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$
Regular expressions may also be used to match the command itself. In this example, a regular expression is used to allow user sid to run the /usr/sbin/groupadd, /usr/sbin/groupmod, /usr/sbin/groupdel, /usr/sbin/useradd, /usr/sbin/usermod, and /usr/sbin/userdel commands as root.
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$
One disadvantage of using a regular expression to
match the command name is that it is not possible to match relative paths
such as ./useradd or
../sbin/useradd. This has security implications when
a regular expression is used for the command name in conjunction with the
negation operator, ‘!’, as such rules
can be trivially bypassed. Because of this, using a negated regular
expression for the command name is
strongly
discouraged. This does not apply to negated commands that only use a
regular expression to match the command arguments. See
Regular
expressions in command names below for more information.
It is possible to include other sudoers files from within the sudoers file currently being parsed using the @include and @includedir directives. For compatibility with sudo versions prior to 1.9.1, #include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide sudoers file in addition to a local, per-machine file. For the sake of this example the site-wide sudoers file will be /etc/sudoers and the per-machine one will be /etc/sudoers.local. To include /etc/sudoers.local from within /etc/sudoers one would use the following line in /etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will
suspend processing of the current file
(/etc/sudoers) and switch to
/etc/sudoers.local. Upon reaching the end of
/etc/sudoers.local, the rest of
/etc/sudoers will be processed. Files that are
included may themselves include other files. A hard limit of 128 nested
include files is enforced to prevent include file loops.
Starting with version 1.9.1, the path to the include file may
contain white space if it is escaped with a backslash
(‘\’). Alternately, the entire path
may be enclosed in double quotes (""), in which case no escaping
is necessary. To include a literal backslash in the path,
‘\\’ should be used.
If the path to the include file is not fully-qualified (does not
begin with a ‘/’), it must be located
in the same directory as the sudoers file it was included from. For example,
if /etc/sudoers contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the
‘%h’ escape, signifying the short form
of the host name. In other words, if the machine's host name is
“xerxes”, then
@include /etc/sudoers.%h
will cause sudo to include the file
/etc/sudoers.xerxes. Any path name separator
characters (‘/’) present in the host
name will be replaced with an underbar
(‘_’) during expansion.
The @includedir directive can be used to create a sudoers.d directory that the system package manager can drop sudoers file rules into as part of package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the
current file and read each file in /etc/sudoers.d,
skipping file names that end in ‘~’ or
contain a ‘.’ character to avoid
causing problems with package manager or editor temporary/backup files.
Files are parsed in sorted lexical order. That is, /etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second. Be aware that because the sorting is lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second. Using a consistent number of leading zeroes in the file names can be used to avoid such problems. After parsing the files in the directory, control returns to the file that contained the @includedir directive.
Unlike files included via @include,
visudo will not edit the files in a
@includedir directory unless one of them contains a syntax
error. It is still possible to run visudo with the
-f flag to edit the files directly, but this will
not catch the redefinition of an alias that is also
present in a different file.
The pound sign (‘#’) is used
to indicate a comment (unless it is part of a #include directive or unless
it occurs in the context of a user name and is followed by one or more
digits, in which case it is treated as a user-ID). Both the comment
character and any text after it, up to the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to succeed. It can be used wherever one might otherwise use a Cmnd_Alias, User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias named ALL will result in a syntax error. Using ALL can be dangerous since in a command context, it allows the user to run any command on the system.
The following option names permitted in an
Option_Spec are also considered reserved words:
CHROOT, TIMEOUT,
CWD, NOTBEFORE and
NOTAFTER. Attempting to define an
alias with the same name as one of the options will result
in a syntax error.
An exclamation point (‘!’)
can be used as a logical not operator in a list or
alias as well as in front of a Cmnd.
This allows one to exclude certain values. For the
‘!’ operator to be effective, there
must be something for it to exclude. For example, to match all users except
for root one would use:
ALL, !root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is different from a true “negation” operator.
Note, however, that using a
‘!’ in conjunction with the built-in
ALL alias to allow a user to run “all but a
few” commands rarely works as intended (see
SECURITY NOTES below).
Long lines can be continued with a backslash
(‘\’) as the last character on the
line.
White space between elements in a list as well as special
syntactic characters in a User Specification
(‘=’,
‘:’,
‘(’,
‘)’) is optional.
The following characters must be escaped with a backslash
(‘\’) when used as part of a word
(e.g., a user name or host name): ‘!’,
‘=’,
‘:’,
‘,’,
‘(’,
‘)’,
‘\’.
sudo's behavior can be modified by
Default_Entry lines, as explained earlier. A list of all
supported Defaults parameters, grouped by type, are listed below.
%group’ as long
as there is not also a system group of the same name. Normally, only
groups of the form ‘%:group’ are
passed to the group_plugin. This flag is
off by default.sudo will set the
HOME environment variable to the home directory of
the target user (which is the runas_default user unless
the -u option is used). This flag is largely
obsolete and has no effect unless the env_reset flag has
been disabled or HOME is present in the
env_keep list, both of which are strongly discouraged.
This flag is off by default.PASSWD and
NOPASSWD tags. This flag is on
by default.-C option which
overrides the default starting point at which sudo
begins closing open file descriptors. This flag is off
by default.sudo is configured to log a command's
input or output, the I/O logs will be compressed using
zlib. This flag is on by default when
sudo is compiled with zlib
support.sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When the
exec_background
flag is enabled and the command is being run in a pseudo-terminal (due to
I/O logging or the use_pty flag), the command will be
run as a background process. Attempts to read from the controlling
terminal (or to change terminal settings) will result in the command being
suspended with the SIGTTIN signal (or
SIGTTOU in the case of terminal settings). If this
happens when sudo is a foreground process, the
command will be granted the controlling terminal and resumed in the
foreground with no user intervention required. The advantage of initially
running the command in the background is that sudo
need not read from the terminal unless the command explicitly requests it.
Otherwise, any terminal input must be passed to the command, whether it
has required it or not (the kernel buffers terminals so it is not possible
to tell whether the command really wants the input). This is different
from historic sudo behavior or when the command is not
being run in a pseudo-terminal.
For this to work seamlessly, the operating system must support
the automatic restarting of system calls. Unfortunately, not all
operating systems do this by default, and even those that do may have
bugs. For example, macOS fails to restart the
tcgetattr(3) and
tcsetattr(3) functions (this is a
bug in macOS). Furthermore, because this behavior depends on the command
stopping with the SIGTTIN or
SIGTTOU signals, programs that catch these
signals and suspend themselves with a different signal (usually
SIGTOP) will not be automatically foregrounded.
Some versions of the linux su(1) command
behave this way. This flag is off by default.
This setting is only supported by version 1.8.7 or higher. It has no effect unless I/O logging is enabled or the use_pty flag is enabled.
visudo will use the value of the
SUDO_EDITOR, VISUAL or
EDITOR environment variables before falling back
on the default editor list. visudo is typically
run as root so this flag may allow a user with
visudo privileges to run arbitrary commands as
root without logging. An alternative is to place a
colon-separated list of “safe” editors int the
editor setting. visudo will then
only use SUDO_EDITOR,
VISUAL or EDITOR if they
match a value specified in editor. If the
env_reset flag is enabled, the
SUDO_EDITOR, VISUAL and/or
EDITOR environment variables must be present in
the env_keep list for the
env_editor
flag to function when visudo is invoked via
sudo. This flag is on by
default.sudo will run the command in a minimal
environment containing the TERM,
PATH, HOME,
MAIL, SHELL,
LOGNAME, USER and
SUDO_* variables. Any variables in the caller's
environment or in the file specified by the
restricted_env_file setting that match the
env_keep and env_check lists are then
added, followed by any variables present in the file specified by the
env_file setting (if any). The contents of the
env_keep and env_check lists, as
modified by global Defaults parameters in sudoers, are
displayed when sudo is run by
root with the -V option. If the
secure_path setting is enabled, its value will be used
for the PATH environment variable. This flag is
on by default.sudo uses the
glob(3) function to do shell-style
globbing when matching path names. However, since it accesses the file
system, glob(3) can take a long time to
complete for some patterns, especially when the pattern references a
network file system that is mounted on demand (auto mounted). The
fast_glob flag causes sudo to
use the fnmatch(3) function, which
does not access the file system to do its matching. The disadvantage of
fast_glob is that it is unable to match relative paths
such as ./ls or ../bin/ls.
This has security implications when path names that include globbing
characters are used with the negation operator,
‘!’, as such rules can be trivially
bypassed. As such, this flag should not be used when the
sudoers file contains rules that contain negated path
names which include globbing characters. This flag is
off by default.sudoers will attempt to
prevent passwords from being logged. It does this by using the regular
expressions in
passprompt_regex
to match a password prompt in the terminal output buffer. When a match is
found, input characters in the I/O log will be replaced with
‘*’ until either a line feed or
carriage return is found in the terminal input or a new terminal output
buffer is received. If, however, a program displays characters as the user
types (such as sudo when
pwfeedback is set), only the first character of the
password will be replaced in the I/O log. This option has no effect unless
log_input or log_ttyin are also set.
This flag is on by default.
This setting is only supported by version 1.9.10 or higher.
hostname’ command) does not
contain the domain name. In other words, instead of myhost you would use
myhost.mydomain.edu. You may still use the short form if you wish (and
even mix the two). This flag is only effective when the
“canonical” host name, as returned by the
getaddrinfo(3) or
gethostbyname(3) function, is a
fully-qualified domain name. This is usually the case when the system is
configured to use DNS for host name resolution.
If the system is configured to use the
/etc/hosts file in preference to DNS, the
“canonical” host name may not be fully-qualified. The
order that sources are queried for host name resolution is usually
specified in the /etc/nsswitch.conf,
/etc/netsvc.conf,
/etc/host.conf, or, in some cases,
/etc/resolv.conf file. In the
/etc/hosts file, the first host name of the
entry is considered to be the “canonical” name; subsequent
names are aliases that are not used by sudoers.
For example, the following hosts file line for the machine
“xyzzy” has the fully-qualified domain name as the
“canonical” host name, and the short version as an
alias.
192.168.1.1 xyzzy.sudo.ws
xyzzyIf the machine's hosts file entry is not formatted properly, the fqdn flag will not be effective if it is queried before DNS.
Beware that when using DNS for host name resolution, turning
on fqdn requires sudoers to
make DNS lookups which renders sudo unusable if
DNS stops working (for example if the machine is disconnected from the
network). Just like with the hosts file, you must use the
“canonical” name as DNS knows it. That is, you may not use
a host alias (CNAME entry) due to performance issues and the fact that
there is no way to get all aliases from DNS.
This flag is off by default.
sudoers cannot
write to the audit log. If enabled, an audit log write failure is not
treated as a fatal error. If disabled, a command may only be run after the
audit event is successfully written. This flag is only effective on
systems for which sudoers supports audit logging,
including FreeBSD, Linux, macOS, and Solaris. This
flag is on by default.sudo will ignore "." or
"" (both denoting the current directory) in the
PATH environment variable; the
PATH itself is not modified. This flag is
on by default.sudoers cannot
write to the I/O log (local or remote). If enabled, an I/O log write
failure is not treated as a fatal error. If disabled, the command will be
terminated if the I/O log cannot be written to. This flag is
off by default.sudoers cannot
write to the log file. If enabled, a log file write failure is not treated
as a fatal error. If disabled, a command may only be run after the log
file entry is successfully written. This flag only has an effect when
sudoers is configured to use file-based logging
via the logfile setting. This flag is
on by default.sudo how to behave when no
specific LDAP entries have been matched, this sudoOption is only
meaningful for the ‘cn=defaults’
section. This flag is off by default.sudo will not produce a warning if it
encounters an unknown Defaults entry in the sudoers file
or an unknown sudoOption in LDAP. This flag is off by
default.sudo will insult users when they enter an
incorrect password. This flag is off by default.sudoers will log commands allowed by the
policy to the system audit log (where supported) as well as to syslog
and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or higher.
sudoers will log commands denied by the
policy to the system audit log (where supported) as well as to syslog
and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or higher.
sudoers will log the exit value of
commands that are run to syslog and/or a log file. If a command was
terminated by a signal, the signal name is logged as well. This flag is
off by default.
This setting is only supported by version 1.9.8 or higher.
sudo will run the command in a
pseudo-terminal (if sudo was run from a terminal)
and log all user input. If the standard input is not connected to the
user's terminal, due to I/O redirection or because the command is part of
a pipeline, that input is also logged. For more information about I/O
logging, see the I/O LOGGING
section. This flag is off by default.sudo will run the command in a
pseudo-terminal (if sudo was run from a terminal)
and log all output that is sent to the user's terminal, the standard
output or the standard error. If the standard output or standard error is
not connected to the user's terminal, due to I/O redirection or because
the command is part of a pipeline, that output is also logged. For more
information about I/O logging, see the
I/O LOGGING section. This flag is
off by default.sudo will enable the TCP keepalive socket
option on the connection to the log server. This enables the periodic
transmission of keepalive messages to the server. If the server does not
respond to a message, the connection will be closed and the running
command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
This flag is on by default.
This setting is only supported by version 1.9.0 or higher.
This setting is only supported by version 1.9.0 or higher.
sudo will log the standard error if it is
not connected to the user's terminal. This can be used to log output to a
pipe or redirected to a file. This flag is off by
default but is enabled when either the log_output flag
or the LOG_OUTPUT command tag is set.sudo will log the standard input if it is
not connected to the user's terminal. This can be used to log input from a
pipe or redirected from a file. This flag is off by
default but is enabled when either the log_input flag or
the LOG_INPUT command tag is set.sudo will log the standard output if it is
not connected to the user's terminal. This can be used to log output to a
pipe or redirected to a file. This flag is off by
default but is enabled when either the log_output flag
or the LOG_OUTPUT command tag is set.sudoers will log when a command spawns a
child process and executes a program using the
execve(2),
execl(3),
execle(3),
execlp(3),
execv(3),
execvp(3),
execvpe(3), or
system(3) library functions. For
example, if a shell is run by sudo, the individual
commands run via the shell will be logged. This flag is
off by default.
The log_subcmds flag uses the same underlying mechanism as the intercept setting. Some commands may not work properly when log_subcmds is enabled, due to the way it intercepts sub-commands. See Preventing shell escapes for more information on what systems support this option and its limitations. This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode.
sudo will run the command in a
pseudo-terminal and log user keystrokes sent to the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_input flag or the
LOG_INPUT command tag is set. If no terminal is
present, for example when running a remote command using
ssh(1), this flag will have no
effect.sudo will run the command in a
pseudo-terminal and log all output displayed on the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_output flag or the
LOG_OUTPUT command tag is set. If no terminal is
present, for example when running a remote command using
ssh(1), this flag will have no
effect.sudo log file. This flag is off
by default.sudo (this includes
sudoedit). No mail will be sent if the user runs
sudo with the -l or
-v option unless there is an authentication error
and the mail_badpass flag is also set. This flag is
off by default.sudo. This flag is off by
default.sudo does not enter the correct password. If the
command the user is attempting to run is not permitted by
sudoers and one of the
mail_all_cmnds, mail_always,
mail_no_host,
mail_no_perms or
mail_no_user
flags are set, this flag will have no effect. This flag is
off by default.sudo but the
command they are trying is not listed in their sudoers
file entry or is explicitly denied. This flag is off by
default.sudoers will look up each group the
user is a member of by group-ID to determine the group name (this is only
done once). The resulting list of the user's group names is used when
matching groups listed in the sudoers file. This works
well on systems where the number of groups listed in the
sudoers file is larger than the number of groups a
typical user belongs to. On systems where group lookups are slow, where
users may belong to a large number of groups, or where the number of
groups listed in the sudoers file is relatively small,
it may be prohibitively expensive and running commands via
sudo may take longer than normal. On such systems
it may be faster to use the match_group_by_gid flag to
avoid resolving the user's group-IDs to group names. In this case,
sudoers must look up any group name listed in the
sudoers file and use the group-ID instead of the group
name when determining whether the user is a member of the group.
If match_group_by_gid is enabled, group
database lookups performed by sudoers will be
keyed by group name as opposed to group-ID. On systems where there are
multiple sources for the group database, it is possible to have
conflicting group names or group-IDs in the local
/etc/group file and the remote group database.
On such systems, enabling or disabling
match_group_by_gid can be used to choose whether group
database queries are performed by name (enabled) or ID (disabled), which
may aid in working around group entry conflicts.
The match_group_by_gid flag has no effect when sudoers data is stored in LDAP. This flag is off by default.
This setting is only supported by version 1.8.18 or higher.
sudo will behave as
if the INTERCEPT tag has been set, unless
overridden by an NOINTERCEPT tag. Some commands
may not work properly when intercept is enabled, due to
the way it intercept sub-commands. See the description of
INTERCEPT and NOINTERCEPT above as well as the
Preventing shell
escapes section at the end of this manual. This flag is
off by default.
This setting is only supported by version 1.9.8 or higher and is incompatible with SELinux RBAC support unless the system supports seccomp(2) filter mode.
LD_PRELOAD (or the equivalent) when running
set-user-ID and set-group-ID programs, effectively disabling intercept
mode. To prevent this from happening, sudoers will
not permit a set-user-ID or set-group-ID program to be run in intercept
mode unless
intercept_allow_setid
is enable. This flag has no effect unless the intercept
flag is enabled or the INTERCEPT tag has been set
for the command. This flag is on by default when the
intercept_type option is set to trace,
otherwise it default to off.
This setting is only supported by version 1.9.8 or higher.
INTERCEPT tag has been set for the
command. This flag is off by default.
This setting is only supported by version 1.9.8 or higher.
sudo will attempt to verify that a command
run in intercept mode has the expected path name, command line arguments
and environment.
The process will be stopped after
execve(2) has completed but before
the new command has had a chance to run. To verify the command,
sudo will read the command's path from
/proc/PID/exe, the command line arguments and
environment from the process's memory, and compare them against the
arguments that were passed to
execve(2). In the event of a
mismatch, the command will be sent a SIGKILL
signal and terminated.
This can help prevent a time of check versus time of use issue
with intercept mode where the
execve(2) arguments could be altered
after the sudoers policy check. The checks can
only be performed if the proc(5) file
system is available. This flag has no effect unless the
intercept flag is enabled or the
INTERCEPT tag has been set for the command and
the intercept_type option is set to
trace.
This setting is incompatible with programs that change their
root directory via chroot(2). If a
program changes its root directory, path names will no longer match
those seen by the sudo parent process and
sub-commands will be terminated before they have a chance to run. This
flag is on by default.
This setting is only supported by version 1.9.12 or higher.
sudo only matched the user name and domain for
netgroups used in a User_List and only matched the host
name and domain for netgroups used in a Host_List. This
flag is off by default.sudo will behave as
if the NOEXEC tag has been set, unless overridden
by an EXEC tag. See the description of
EXEC and NOEXEC above as well as the
Preventing shell
escapes section at the end of this manual. This flag is
off by default.sudo's -n option is
specified). This allows authentication methods that don't require user
interaction to succeed. Authentication methods that require input from the
user's terminal will still fail. If disabled, authentication will not be
attempted in non-interactive mode. This flag is off by
default.
This setting is only supported by version 1.9.10 or higher.
sudo
will perform PAM account validation for the invoking user by default. The
actual checks performed depend on which PAM modules are configured. If
enabled, account validation will be performed regardless of whether or not
a password is required. This flag is on by default.
This setting is only supported by version 1.8.28 or higher.
sudo
will set the PAM remote host value to the name of the local host when the
pam_rhost flag is enabled. On Linux systems, enabling
pam_rhost may result in DNS lookups of the local host
name when PAM is initialized. On Solaris versions prior to Solaris 8,
pam_rhost must be enabled if pam_ruser
is also enabled to avoid a crash in the Solaris PAM implementation.
This flag is off by default on systems other than Solaris.
This setting is only supported by version 1.9.0 or higher.
sudo
will set the PAM remote user value to the name of the user that invoked
sudo when the pam_ruser flag is enabled. This flag is
on by default.
This setting is only supported by version 1.9.0 or higher.
sudo
will create a new PAM session for the command to be run in. Unless
sudo is given the -i or
-s options, PAM session modules are run with the
“silent” flag enabled. This prevents last login information
from being displayed for every command on some systems. Disabling
pam_session may be needed on older PAM implementations
or on operating systems where opening a PAM session changes the utmp or
wtmp files. If PAM session support is disabled, resource limits may not be
updated for the command being run. If pam_session,
pam_setcred, and use_pty are disabled,
log_servers has not been set and I/O logging has not
been configured, sudo will execute the command
directly instead of running it as a child process. This flag is
on by default.
This setting is only supported by version 1.8.7 or higher.
sudo
will attempt to establish credentials for the target user by default, if
supported by the underlying authentication system. One example of a
credential is a Kerberos ticket. If pam_session,
pam_setcred, and use_pty are disabled,
log_servers has not been set and I/O logging has not
been configured, sudo will execute the command
directly instead of running it as a child process. This flag is
on by default.
This setting is only supported by version 1.8.8 or higher.
SUDO_PROMPT environment variable will always be
used and will replace the prompt provided by a PAM module or other
authentication method. This flag is off by default.sudo will tell the user when a command
could not be found in their PATH environment
variable. Some sites may wish to disable this as it could be used to
gather information on the location of executables that the normal user
does not have access to. The disadvantage is that if the executable is
simply not in the user's PATH,
sudo will tell the user that they are not allowed
to run it, which can be confusing. This flag is on by
default.sudo will initialize the group vector
to the list of groups the target user is in. When
preserve_groups
is set, the user's existing group vector is left unaltered. The real and
effective group-IDs, however, are still set to match the target user. This
flag is off by default.sudo reads the password like most
other Unix programs, by turning off echo until the user hits the return
(or enter) key. Some users become confused by this as it appears to them
that sudo has hung at this point. When
pwfeedback is set, sudo will
provide visual feedback when the user presses a key. This does have a
security impact as an onlooker may be able to determine the length of the
password being entered. This flag is off by
default.sudo will only run when the user is logged
in to a real tty. When this flag is set, sudo can
only be run from a login session and not via other means such as
cron(8) or cgi-bin scripts. This flag is
off by default.sudo too. Disabling this prevents users from
“chaining” sudo commands to get a
root shell by doing something like
‘sudo sudo /bin/sh’. Note, however,
that turning off root_sudo will also prevent
root from running sudoedit.
Disabling root_sudo provides no real additional
security; it exists purely for historical reasons. This flag is
on by default.sudo will prompt for the
root password instead of the password of the invoking
user when running a command or editing a file. This flag is
off by default.This setting is only supported by version 1.8.30 or higher.
Older versions of sudo always allowed matching
of unknown user and group IDs.
sudo will only run commands as a user
whose shell appears in the /etc/shells file, even
if the invoking user's Runas_List would otherwise permit
it. If no /etc/shells file is present, a
system-dependent list of built-in default shells is used. On many
operating systems, system users such as “bin”, do not have a
valid shell and this flag can be used to prevent commands from being run
as those users. This flag is off by default.
This setting is only supported by version 1.8.30 or higher.
sudo will prompt for the password of the
user defined by the runas_default option (defaults to
root) instead of the password of the invoking user when
running a command or editing a file. This flag is off by
default.sudo is invoked with the
-s option, the HOME
environment variable will be set to the home directory of the target user
(which is the runas_default user unless the
-u option is used). This flag is largely obsolete
and has no effect unless the env_reset flag has been
disabled or HOME is present in the
env_keep list, both of which are strongly discouraged.
This flag is off by default.sudo will set the
LOGNAME and USER
environment variables to the name of the target user (the user specified
by runas_default unless the -u
option is given). However, since some programs (including the RCS revision
control system) use LOGNAME to determine the real
identity of the user, it may be desirable to change this behavior. This
can be done by negating the set_logname option. The
set_logname option will have no effect if the
env_reset option has not been disabled and the
env_keep list contains LOGNAME
or USER. This flag is on by
default.sudo will create an entry in the
utmp (or utmpx) file when a pseudo-terminal is allocated. A
pseudo-terminal is allocated by sudo when it is
running in a terminal and one or more of the log_input,
log_output, log_stdin,
log_stdout, log_stderr,
log_ttyin, log_ttyout, or
use_pty flags is enabled. By default, the new entry will
be a copy of the user's existing utmp entry (if any), with the tty, time,
type, and pid fields updated. This flag is on by
default.-E option. Additionally,
environment variables set via the command line are not subject to the
restrictions imposed by env_check,
env_delete, or env_keep. As such, only
trusted users should be allowed to set variables in this manner. This flag
is off by default.sudo is invoked with no arguments it
acts as if the -s option had been given. That is,
it runs a shell as root (the shell is determined by the
SHELL environment variable if it is set, falling
back on the shell listed in the invoking user's /etc/passwd entry if not).
This flag is off by default.sudo executes a command the real
and effective user-IDs are set to the target user (root
by default). This option changes that behavior such that the real user-ID
is left as the invoking user's user-ID. In other words, this makes
sudo act as a set-user-ID wrapper. This can be
useful on systems that disable some potentially dangerous functionality
when a program is run set-user-ID. This option is only effective on
systems that support either the
setreuid(2) or
setresuid(2) system call. This flag
is off by default.sudoedit will check all directory
components of the path to be edited for writability by the invoking user.
Symbolic links will not be followed in writable directories and
sudoedit will refuse to edit a file located in a
writable directory. These restrictions are not enforced when
sudoedit is run by root. On some
systems, if all directory components of the path to be edited are not
readable by the target user, sudoedit will be
unable to edit the file. This flag is on by default.
This setting was first introduced in version 1.8.15 but initially suffered from a race condition. The check for symbolic links in writable intermediate directories was added in version 1.8.16.
sudoedit will not follow symbolic
links when opening files. The sudoedit_follow option can
be enabled to allow sudoedit to open symbolic
links. It may be overridden on a per-command basis by the
FOLLOW and NOFOLLOW tags.
This flag is off by default.
This setting is only supported by version 1.8.15 or higher.
This setting is only supported by version 1.8.21 or higher.
sudo will prompt for the password of the
user specified by the -u option (defaults to the
value of runas_default) instead of the password of the
invoking user when running a command or editing a file. This flag
precludes the use of a user-ID not listed in the passwd database as an
argument to the -u option. This flag is
off by default.sudo will use a separate record in the
time stamp file for each terminal. If disabled, a single record is used
for all login sessions.
This option has been superseded by the timestamp_type option.
sudo will set the umask as specified in
the sudoers file without modification. This makes it
possible to specify a umask in the sudoers file that is
more permissive than the user's own umask and matches historical behavior.
If umask_override is not set,
sudo will set the umask to be the union of the
user's umask and what is specified in sudoers. This flag
is off by default.+’), may be used in place of a user
or host. For LDAP-based sudoers, netgroup support requires an expensive
sub-string match on the server unless the
NETGROUP_BASE
directive is present in the /etc/ldap.conf file.
If netgroups are not needed, this option can be disabled to reduce the
load on the LDAP server. This flag is on by
default.sudo is running in a terminal, the
command will be run in a new pseudo-terminal. If the
sudo process is not attached to a terminal,
use_pty has no effect.
A malicious program run under sudo may
be capable of injecting commands into the user's terminal or running a
background process that retains access to the user's terminal device
even after the main program has finished executing. By running the
command in a separate pseudo-terminal, this attack is no longer
possible. This flag is on by default for
sudo 1.9.14 and above.
This setting is only supported by version 1.8.20 or higher.
sudo will store the name of the runas user
when updating the utmp (or utmpx) file. By default,
sudo stores the name of the invoking user. This
flag is off by default.sudo will refuse to run if the user
must enter a password but it is not possible to disable echo on the
terminal. If the
visiblepw
flag is set, sudo will prompt for a password even
when it would be visible on the screen. This makes it possible to run
things like ‘ssh somehost sudo ls’
since by default, ssh(1) does not allocate
a tty when running a command. This flag is off by
default.Integers:
sudo will close all
open file descriptors other than standard input, standard output, and
standard error (file descriptors 0-2). The
closefrom
option can be used to specify a different file descriptor at which to
start closing. The default is 3.This setting is only supported by version 1.8.20 or higher.
This setting is only supported by version 1.9.0 or higher.
%{seq}’ escape in the I/O log file
(see the iolog_dir description below for more
information). While the value substituted for
‘%{seq}’ is in base 36,
maxseq itself should be expressed in decimal. Values
larger than 2176782336 (which corresponds to the base 36 sequence number
“ZZZZZZ”) will be silently truncated to 2176782336. The
default value is 2176782336.
Once the local sequence number reaches the value of
maxseq, it will “roll over” to zero,
after which sudoers will truncate and re-use any
existing I/O log path names.
This setting is only supported by version 1.8.7 or higher.
sudo logs the failure and exits. The default is
3.sudoers creates log
messages up to 980 bytes which corresponds to the historic
BSD syslog implementation which used a 1024 byte
buffer to store the message, date, hostname, and program name. To prevent
syslog messages from being truncated, sudoers will
split up log messages that are larger than syslog_maxlen
bytes. When a message is split, additional parts will include the string
“(command continued)” after the user name and before the
continued command line arguments.
This setting is only supported by version 1.8.19 or higher.
Integers that can be used in a boolean context:
sudo password prompt
times out, or 0 for no timeout. The timeout may include a fractional
component if minute granularity is insufficient, for example 2.5. The
default is 5.sudo will
ask for a password again. The timeout may include a fractional component
if minute granularity is insufficient, for example 2.5. The default is 5.
Set this to 0 to always prompt for a password. If set to a value less than
0 the user's time stamp will not expire until the system is rebooted. This
can be used to allow users to create or delete their own time stamps via
‘sudo -v’ and
‘sudo -k’ respectively.sudoers from
changing the umask. Unless the umask_override flag is
set, the actual umask will be the union of the user's umask and the value
of the umask setting, which defaults to 0022. This
guarantees that sudo never lowers the umask when
running a command.
If umask is explicitly set in
sudoers, it will override any umask setting in PAM or
login.conf. If umask is not set in
sudoers, the umask specified by PAM or login.conf will
take precedence. The umask setting in PAM is not used for
sudoedit, which does not create a new PAM
session.
Strings:
%d’ escape which
will expand to the number of failed password attempts. If set, it
overrides the default message, “%d incorrect password
attempt(s)”.:’) separated list of
editor path names used by sudoedit and
visudo. For sudoedit, this
list is used to find an editor when none of the
SUDO_EDITOR, VISUAL or
EDITOR environment variables are set to an editor
that exists and is executable. For visudo, it is
used as a white list of allowed editors; visudo
will choose the editor that matches the user's
SUDO_EDITOR, VISUAL or
EDITOR environment variable if possible, or the
first editor in the list that exists and is executable if not. Unless
invoked as sudoedit, sudo
does not preserve the SUDO_EDITOR,
VISUAL or EDITOR
environment variables unless they are present in the
env_keep list or the env_reset option
is disabled. The default is ~.sudo's SELinux RBAC support.The default is to use trace if it is supported by the system and dso if it is not.
LOG_INPUT or LOG_OUTPUT
tags are present for a command. The session sequence number, if any, is
stored in the directory. The default is
/var/log/sudo-io.
The following percent
(‘%’) escape sequences are
supported:
In addition, any escape sequences supported by the system's strftime(3) function will be expanded.
To include a literal ‘%’
character, the string ‘%%’ should
be used.
Any path name separator characters
(‘/’) present in the user, group
or host name will be replaced with an underbar
(‘_’) during expansion.
LOG_INPUT or LOG_OUTPUT
tags are present for a command. iolog_file may contain
directory components. The default is
‘%{seq}’.
See the iolog_dir option above for a list of
supported percent (‘%’) escape
sequences.
In addition to the escape sequences, path names that end in six or more Xs will have the Xs replaced with a unique combination of digits and letters, similar to the mktemp(3) function.
If the path created by concatenating iolog_dir and iolog_file already exists, the existing I/O log file will be truncated and overwritten unless iolog_file ends in six or more Xs.
sudo will flush I/O log data to disk after
each write instead of buffering it. This makes it possible to view the
logs in real-time as the program is executing but may significantly reduce
the effectiveness of I/O log compression. This flag is
off by default.
This setting is only supported by version 1.8.20 or higher.
This setting is only supported by version 1.8.19 or higher.
This setting is only supported by version 1.8.19 or higher.
This setting can be useful when the I/O logs are stored on a
Network File System (NFS) share. Having a dedicated user own the I/O log
files means that sudoers does not write to the
log files as user-ID 0, which is usually not permitted by NFS.
This setting is only supported by version 1.8.19 or higher.
sudo stores per-user
lecture status files. Once a user has received the lecture, a zero-length
file is created in this directory so that sudo
will not lecture the user again. This directory should
not be cleared when the system reboots. The default is
/var/db/sudo/lectured.This setting is only supported by version 1.9.0 or higher.
sudo client's certificate file, in
PEM format. This setting is required when the remote log server is secured
with TLS and client certificate validation is enabled. For
sudo_logsrvd, client certificate validation is
controlled by the tls_checkpeer option, which defaults
to false.
This setting is only supported by version 1.9.0 or higher.
sudo client's private key file, in
PEM format. This setting is required when the remote log server is secured
with TLS and client certificate validation is enabled. For
sudo_logsrvd, client certificate validation is
controlled by the tls_checkpeer flag, which defaults to
false.
This setting is only supported by version 1.9.0 or higher.
%h’ will expand to the host name of
the machine. Default is “*** SECURITY information for %h
***”.sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should now be set in the
sudo.conf(5) file.-A option is specified. The default value
is either ‘sudo’ or
‘sudo’, depending on whether or not
the -i option is also specified. See the
description of pam_service for more information.
This setting is only supported by version 1.9.9 or higher.
-i option is specified. The default value
is ‘sudo’. See the description of
pam_service for more information.
This setting is only supported by version 1.8.8 or higher.
sudo’.
This setting is only supported by version 1.8.8 or higher.
-p option or the
SUDO_PROMPT environment variable. The following
percent (‘%’) escape sequences are
supported:
%’ characters
are collapsed into a single ‘%’
characterOn systems that use PAM for authentication, passprompt will only be used if the prompt provided by the PAM module matches the string “Password: ” or “username's Password: ”. This ensures that the passprompt setting does not interfere with challenge-response style authentication. The passprompt_override flag can be used to change this behavior.
The default value is ‘Password:
’.
-u
option is not specified on the command line. This defaults to
root.C’.sudoers uses per-user time stamp files for
credential caching. The timestamp_type option can be
used to specify the type of time stamp record used. It has the following
possible values:
sudo is used multiple times in a pipeline, but
this does not affect authentication.sudo with a different parent process
ID, for example from a shell script, will be authenticated
separately.The default value is tty.
This setting is only supported by version 1.8.21 or higher.
sudo stores its time stamp
files. This directory should be cleared when the system reboots. The
default is /run/sudo/ts.Strings that can be used in a boolean context:
sudo. Only available if
sudo is configured with the
--enable-admin-flag option. The default value is
~/.sudo_as_admin_successful.VARIABLE=value’ or
‘export VARIABLE=value’. The value
may optionally be enclosed in single or double quotes. Variables in this
file are only added if the variable does not already exist in the
environment. This file is considered to be part of the security policy,
its contents are not subject to other sudo
environment restrictions such as env_keep and
env_check.%’ prefix. This is not set by
default.sudo will execute a command by
its path or by an open file descriptor. It has the following possible
values:
The default value is digest_only. This avoids a time of check versus time of use race condition when the command is located in a directory writable by the invoking user.
fdexec will change the first element of the
argument vector for scripts ($0 in the shell) due to the way the kernel
runs script interpreters. Instead of being a normal path, it will refer
to a file descriptor. For example, /dev/fd/4 on
Solaris and /proc/self/fd/4 on Linux. A
workaround is to use the SUDO_COMMAND
environment variable instead.
The fdexec setting is only used when the command is matched by path name. It has no effect if the command is matched by the built-in ALL alias.
This setting is only supported by version 1.8.20 or higher. If the operating system does not support the fexecve(2) system call, this setting has no effect.
sudoers group plugin with
optional arguments. The string should consist of the plugin path, either
fully-qualified or relative to the
/usr/libexec/sudo directory, followed by any
configuration arguments the plugin requires. These arguments (if any) will
be passed to the plugin's initialization function. If arguments are
present, the string must be enclosed in double quotes ("").
On 64-bit systems, if the plugin is present but cannot be
loaded, sudoers will look for a 64-bit version
and, if it exists, load that as a fallback. The exact rules for this
vary by system. On Solaris, if the plugin is stored in a directory
ending in “lib”, sudoers will
create a fallback path by appending “/64” to the directory
name; /usr/lib/group_plugin.so becomes
/usr/lib/64/group_plugin.so. On Linux, a
directory ending in “lib” will be transformed to
“lib64” as the fallback path;
/usr/lib/group_plugin.so becomes
/usr/lib64/group_plugin.so. On all other
systems, the fallback path is generated by adding a “64”
before the file extension; group_plugin.so
becomes group_plugin64.so.
On AIX systems, the plugin may be either a shared object
ending in ‘.so’ or an archive file
containing a shared object ending in
‘.a’ with the name of the shared
object in parentheses at the end.
For more information see GROUP PROVIDER PLUGINS.
sudo.If no value is specified, a value of once is implied. Negating the option results in a value of never being used. The default value is once.
sudo
lecture that will be used in place of the standard lecture if the named
file exists. By default, sudo uses a built-in
lecture.sudo with the -l option.
It has the following possible values:
NOPASSWD flag set to avoid
entering a password.-l option.NOPASSWD flag
set to avoid entering a password.-l option.If no value is specified, a value of any is implied. Negating the option results in a value of never being used. The default value is any.
This setting affects logs sent via syslog(3) as well as the file specified by the logfile setting, if any. The default value is sudo.
sudo log file (not the syslog log
file). Setting a path turns on logging to a file; negating this option
turns it off. By default, sudo logs via
syslog.-t.sudo from sending mail). Defaults to the path to
sendmail found at configure time.sudo
interpreting the ‘@’ sign. Defaults
to the name of the user running sudo.sudo from sending mail). The address should be
enclosed in double quotes ("") to protect against
sudo interpreting the
‘@’ sign. Defaults to root.VARIABLE=value’ or
‘export VARIABLE=value’. The value
may optionally be enclosed in single or double quotes. Variables in this
file are only added if the variable does not already exist in the
environment. Unlike env_file, the file's contents are
not trusted and are processed in a manner similar to that of the invoking
user's environment. If env_reset is enabled, variables
in the file will only be added if they are matched by either the
env_check or env_keep list. If
env_reset is disabled, variables in the file are added
as long as they are not matched by the env_delete list.
In either case, the contents of restricted_env_file are
processed before the contents of env_file.sudo will use this value for the root
directory when running a command. The special value “*” will
allow the user to specify the root directory via
sudo's -R option. See the
Chroot_Spec section for more
details.
It is only possible to use runchroot as a command-specific Defaults setting if the command exists with the same path both inside and outside the chroot jail. This restriction does not apply to global, host, or user-based Defaults settings or to a Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or higher.
sudo will use this value for the working
directory when running a command. The special value “*” will
allow the user to specify the working directory via
sudo's -D option. See the
Chdir_Spec section for more details.
This setting is only supported by version 1.9.3 or higher.
sudo will use this value in place of the
user's PATH environment variable. This option can
be used to reset the PATH to a known good value
that contains directories for system administrator commands such as
/usr/sbin.
Users in the group specified by the exempt_group option are not affected by secure_path. This option is not set by default.
The following syslog facilities are supported: authpriv (if your OS supports it), auth, daemon, user, local0, local1, local2, local3, local4, local5, local6, and local7.
The following syslog priorities are supported: alert, crit, debug, emerg, err, info, notice, warning, and none. Negating the option or setting it to a value of none will disable logging of unsuccessful commands.
See syslog_badpri for the list of supported syslog priorities. Negating the option or setting it to a value of none will disable logging of successful commands.
sudo with the -v option.
It has the following possible values:
NOPASSWD flag set to avoid
entering a password.-v option.NOPASSWD flag
set to avoid entering a password.-v option.If no value is specified, a value of all is implied. Negating the option results in a value of never being used. The default value is all.
Lists that can be used in a boolean context:
TZ, “safe” means that the variable's
value does not contain any ‘%’ or
‘/’ characters. This can be used to
guard against printf-style format vulnerabilities in poorly-written
programs. The TZ variable is considered unsafe if
any of the following are true:
:’), that does not match
the location of the zoneinfo directory.PATH_MAX.The argument may be a double-quoted, space-separated list or a
single value without double-quotes. The list can be replaced, added to,
deleted from, or disabled by using the
‘=’,
‘+=’,
‘-=’, and
‘!’ operators respectively.
Regardless of whether the env_reset option is enabled
or disabled, variables specified by env_check will be
preserved in the environment if they pass the aforementioned check. The
global list of environment variables to check is displayed when
sudo is run by root with the
-V option.
=’,
‘+=’,
‘-=’, and
‘!’ operators respectively. The
global list of environment variables to remove is displayed when
sudo is run by root with the
-V option. Many operating systems will remove
potentially dangerous variables from the environment of any set-user-ID
process (such as sudo).sudo-spawned
processes will receive. The argument may be a double-quoted,
space-separated list or a single value without double-quotes. The list can
be replaced, added to, deleted from, or disabled by using the
‘=’,
‘+=’,
‘-=’, and
‘!’ operators respectively. The
global list of variables to keep is displayed when
sudo is run by root with the
-V option.
Preserving the HOME environment
variable has security implications since many programs use it when
searching for configuration or data files. Adding
HOME to env_keep may enable a
user to run unrestricted commands via sudo and
is strongly discouraged. Users wishing to edit files with
sudo should run sudoedit
(or sudo -e) to get
their accustomed editor configuration instead of invoking the editor
directly.
sudo_logsrvd or another service that implements
the protocol described by
sudo_logsrv.proto(5).
Server addresses should be of the form “host[:port][(tls)]”. The host portion may be a host name, an IPv4 address, or an IPv6 address in square brackets.
If the optional tls flag is present, the connection will be secured with Transport Layer Security (TLS) version 1.2 or 1.3. Versions of TLS prior to 1.2 are not supported.
If a port is specified, it may either be a port number or a well-known service name as defined by the system service name database. If no port is specified, port 30343 will be used for plaintext connections and port 30344 will be used for TLS connections.
When log_servers is set, event
log data will be logged both locally (see the syslog
and log_file
settings) as well as remotely, but I/O log data will only be logged
remotely. If multiple hosts are specified, they will be attempted in
reverse order. If no log servers are available, the user will not be
able to run a command unless either the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
Likewise, if the connection to the log server is interrupted while
sudo is running, the command will be terminated
unless the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O logging
disabled) is set.
This setting is only supported by version 1.9.0 or higher.
This setting is only supported by version 1.9.10 or higher.
The sudoers plugin supports its own plugin
interface to allow non-Unix group lookups which can query a group source
other than the standard Unix group database. This can be used to implement
support for the nonunix_group syntax described
earlier.
Group provider plugins are specified via the group_plugin setting. The argument to group_plugin should consist of the plugin path, either fully-qualified or relative to the /usr/libexec/sudo directory, followed by any configuration options the plugin requires. These options (if specified) will be passed to the plugin's initialization function. If options are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
Defaults group_plugin="group_file.so /etc/sudo-group"
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(5).
sudoers can log events in either JSON or
sudo format, this section describes the
sudo log format. Depending on sudoers
configuration, sudoers can log events via
syslog(3), to a local log file, or both.
The log format is almost identical in both cases. Any control characters
present in the log data are formatted in octal with a leading
‘#’ character. For example, a
horizontal tab is stored as ‘#011’ and
an embedded carriage return is stored as
‘#015’. In addition, space characters
in the command path are stored as
‘#040’. Command line arguments that
contain spaces are enclosed in single quotes (''). This makes it possible to
distinguish multiple command line arguments from a single argument that
contains spaces. Literal single quotes and backslash characters
(‘\’) in command line arguments are
escaped with a backslash.
Commands that sudo runs are logged using the following format (split into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \
PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
sudo was run on. This field
is only present when logging via
syslog(3).sudo.sudo was run on, or “unknown” if
there was no terminal present.sudo was run
in.Messages are logged using the locale specified by
sudoers_locale, which defaults to the
‘C’ locale.
If the user is not allowed to run the command, the reason for the denial will follow the user name. Possible reasons include:
-n option was specified but a password was
required.If an error occurs, sudoers will log a
message and, in most cases, send a message to the administrator via email.
Possible errors include:
sudoers encountered an error when parsing the
specified file. In some cases, the actual error may be one line above or
below the line number listed, depending on the type of error.sudo from running,
but the sudoers file should be checked using
visudo.sudoers tries to open the
sudoers file using group permissions to avoid this
problem. Consider either changing the ownership of
/etc/sudoers or adding an argument like
“sudoers_uid=N” (where ‘N’ is the user-ID that
owns the sudoers file) to the end of the
sudoers Plugin line in the
sudo.conf(5) file.sudoers Plugin line in the
sudo.conf(5) file.sudoers
Plugin line in the
sudo.conf(5) file.sudoers Plugin line in the
sudo.conf(5) file.sudoers was unable to read or create the user's
time stamp file. This can happen when timestampowner is
set to a user other than root and the mode on
/run/sudo is not searchable by group or other. The
default mode for /run/sudo is 0711.sudoers was unable to write to the user's time
stamp file.sudoers will ignore the time stamp directory until
the owner is corrected.sudoers will ignore the time
stamp directory until the mode is corrected.By default, sudoers logs messages via
syslog(3). The
date,
hostname, and progname fields are added
by the system's syslog(3) function, not
sudoers itself. As such, they may vary in format on
different systems.
The maximum size of syslog messages varies from system to system. The syslog_maxlen setting can be used to change the maximum syslog message size from the default value of 980 bytes. For more information, see the description of syslog_maxlen.
If the logfile option is set,
sudoers will log to a local file, such as
/var/log/sudo. When logging to a file,
sudoers uses a format similar to
syslog(3), with a few important
differences:
!’), word wrap will
be disabled.When I/O logging is enabled, sudo will
runs the command in a pseudo-terminal, logging user input and/or output,
depending on which sudoers flags are enabled. There
are five distinct types of I/O that can be logged, each with a corresponding
sudoers flag.
| Type | Flag | Description |
| terminal input | log_ttyin | keystrokes entered by the user |
| terminal output | log_ttyout | command output displayed to the screen |
| standard input | log_stdin | input from a pipe or a file |
| standard output | log_stdout | output to a pipe or a file |
| standard error | log_stderr | output to a pipe or a file |
In addition to flags described the above, the
log_input flag and LOG_INPUT
command tag set both log_ttyin and
log_stdin. The log_output flag and
LOG_OUTPUT command tag set
log_ttyout, log_stdout, and
log_stderr.
To capture terminal input and output, sudo
run the command in a pseudo-terminal, logging the input and output before
passing it on to the user. To capture the standard input, standard output or
standard error, sudo uses a pipe to interpose itself
between the input or output stream, logging the I/O before passing it to the
other end of the pipe.
I/O can be logged either to the local machine or to a remote log
server. For local logs, I/O is logged to the directory specified by the
iolog_dir option (/var/log/sudo-io
by default) using a unique session ID that is included in the
sudo log line, prefixed with
‘TSID=’. The
iolog_file option may be used to control the format of the
session ID. For remote logs, the log_servers setting is
used to specify one or more log servers running
sudo_logsrvd or another server that implements the
protocol described by
sudo_logsrv.proto(5).
When logging standard input, anything sent to the standard input
will be consumed, regardless of whether or not the command run via
sudo is actively reading the standard input. This
may have unexpected results when using sudo in a
shell script that expects to process the standard input. For example, given
the following shell script:
#!/bin/sh sudo echo testing echo done
It will behave as expected when the script is passed to the shell as a an argument:
$ sh test.sh testing done
However, if the script is passed to the shell on the standard
input, the ‘sudo echo testing’ command
will consume the rest of the script. This means that the
‘echo done’ statement is never
executed.
$ sh -s < test.sh testing
There are several ways to work around this problem:
sudo that does not need to
read the standard input.
sudo echo testing < /dev/null
sh test.sh
Defaults!/bin/echo !log_stdin
Depending on the command, it may not be desirable to log the standard input or standard output. For example, I/O logging of commands that send or receive large amount of data via the standard output or standard input such as rsync(1) and tar(1) could fill up the log file system with superfluous data. It is possible to disable logging of the standard input and standard output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync # Log input and output but omit stdin and stdout when copying files. Defaults log_input, log_output Defaults!COPY_CMDS !log_stdin, !log_stdout
However, be aware that using the
log_input flag or the LOG_INPUT
command tag will also enable log_stdin. Likewise, the
log_ouput flag
or the LOG_OUTPUT command tag will enable
log_stdout and
log_stderr.
Careful ordering of rules may be necessary to achieve the results that you
expect.
For both local and remote I/O logs, each log is stored in a separate directory that contains the following files:
sudo, the name
of the target user, the name of the target group (optional), the terminal
that sudo was run from, and the number of lines
and columns of the terminal. The second and third lines contain the
working directory the command was run from and the path name of the
command itself (with arguments if present).sudo
was run.sudo.sudo from. If the command was run in a
pseudo-terminal,
ttyname
will be different from the terminal the command actually ran in.sudo 1.8.7 terminal
outputsudo
was run from a terminal. No post-processing is performed. For manual
viewing, you may wish to convert carriage return characters in the log to
line feeds. For example: ‘gunzip -c ttyin | tr
"\r" "\n"’sudo was run from a terminal.All files other than log
are compressed in gzip format unless the
compress_io
flag has been disabled. Due to buffering, it is not normally possible to
display the I/O logs in real-time as the program is executing. The I/O log
data will not be complete until the program run by
sudo has exited or has been terminated by a signal.
The
iolog_flush
flag can be used to disable buffering, in which case I/O log data is written
to disk as soon as it is available. The output portion of an I/O log file
can be viewed with the sudoreplay(8)
utility, which can also be used to list or search the available logs.
User input may contain sensitive information such as passwords
(even if they are not echoed to the screen), which will be stored in the log
file unencrypted. In most cases, logging the command output via
log_output or LOG_OUTPUT is all
that is required. When logging input, consider disabling the
log_passwords flag.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the number of I/O
logs. The simplest way to limit the number of I/O is by setting the
maxseq option to the maximum number of logs you wish to
store. Once the I/O log sequence number reaches maxseq, it
will be reset to zero and sudoers will truncate and
re-use any existing I/O logs.
sudoers
security policysudoers security policy-i mode on AIX and Linux
systemsBelow are example sudoers file entries. Admittedly, some of these are a bit contrived. First, we allow a few environment variables to pass and then define our aliases:
# Run X applications through sudo; HOME is used to find the # .Xauthority file. Other programs use HOME to locate configuration # files and this may lead to privilege escalation! Defaults env_keep += "DISPLAY HOME" # User alias specification User_Alias FULLTIMERS = millert, mikef, dowdy User_Alias PARTTIMERS = bostley, jwfox, crawl User_Alias WEBADMIN = will, wendy, wim # Runas alias specification Runas_Alias OP = root, operator Runas_Alias DB = oracle, sybase Runas_Alias ADMINGRP = adm, oper # Host alias specification Host_Alias SPARC = bigtime, eclipse, moet, anchor :\ SGI = grolsch, dandelion, black :\ ALPHA = widget, thalamus, foobar :\ HPPA = boa, nag, python Host_Alias CUNETS = 128.138.0.0/255.255.0.0 Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0 Host_Alias SERVERS = primary, mail, www, ns Host_Alias CDROM = orion, perseus, hercules # Cmnd alias specification Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\ /usr/sbin/restore, /usr/sbin/rrestore,\ sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \ /home/operator/bin/start_backups Cmnd_Alias KILL = /usr/bin/kill Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown Cmnd_Alias HALT = /usr/sbin/halt Cmnd_Alias REBOOT = /usr/sbin/reboot Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\ /usr/local/bin/tcsh, /usr/bin/rsh,\ /usr/local/bin/zsh Cmnd_Alias SU = /usr/bin/su Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want
sudo to log via
syslog(3) using the
auth facility in all cases and for commands to be run with
the target user's home directory as the working directory. We don't want to
subject the full time staff to the sudo lecture and
we want to allow them to run commands in a
chroot(2) “sandbox” via the
-R option. User millert need not
provide a password and we don't want to reset the
LOGNAME or USER environment
variables when running commands as root. Additionally, on
the machines in the SERVERS
Host_Alias, we keep an additional local log file and make
sure we log the year in each log line since the log entries will be kept
around for several years. Lastly, we disable shell escapes for the commands
in the PAGERS Cmnd_Alias
(/usr/bin/more, /usr/bin/pg
and /usr/bin/less). This will not effectively
constrain users with sudo ALL
privileges.
# Override built-in defaults Defaults syslog=auth,runcwd=~ Defaults>root !set_logname Defaults:FULLTIMERS !lecture,runchroot=* Defaults:millert !authenticate Defaults@SERVERS log_year, logfile=/var/log/sudo.log Defaults!PAGERS noexec
The User specification is the part that actually determines who may run what.
root ALL = (ALL) ALL %wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins
bostley,
jwfox,
and
crawl)
may run any command on any host but they must authenticate themselves first
(since the entry lacks the NOPASSWD tag).
jack CSNETS = ALL
The user
jack may run any
command on the machines in the CSNETS alias (the
networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those
networks, only 128.138.204.0 has an explicit netmask (in CIDR notation)
indicating it is a class C network. For the other networks in
CSNETS, the local machine's netmask will be used
during matching.
lisa CUNETS = ALL
The user
lisa may run any
command on any host in the CUNETS alias (the class B
network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\ sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to
simple maintenance. Here, those are commands related to backups, killing
processes, the printing system, shutting down the system, and any commands
in the directory /usr/oper/bin/. One command in the
DUMPS Cmnd_Alias includes a sha224 digest,
/home/operator/bin/start_backups. This is because
the directory containing the script is writable by the operator user. If the
script is modified (resulting in a digest mismatch) it will no longer be
possible to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root* %opers ALL = (: ADMINGRP) /usr/sbin/
Users in the
opers group may run
commands in /usr/sbin/ as themselves with any group
in the ADMINGRP Runas_Alias (the
adm and
oper
groups).
The user
pete is allowed to
change anyone's password except for root on the
HPPA machines. Because command line arguments are
matched as a single, concatenated string, the
‘*’ wildcard will match
multiple
words. This example assumes that
passwd(1) does not take multiple user
names on the command line. On systems with GNU
getopt(3), options to
passwd(1) may be specified after the user
argument. As a result, this rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user
bob may run anything
on the SPARC and SGI
machines as any user listed in the OP
Runas_Alias (root and
operator.)
jim +biglab = ALL
The user
jim may run any
command on machines in the
biglab
netgroup. sudo knows that “biglab” is
a netgroup due to the ‘+’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as well as add and remove users, so they are allowed to run those commands on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user
fred can run
commands as any user in the DB
Runas_Alias
(oracle
or
sybase)
without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user
john may su to anyone except root but he
is not allowed to specify any options to the
su(1) command.
jen ALL, !SERVERS = ALL
The user
jen may run any
command on any machine except for those in the
SERVERS Host_Alias (primary, mail,
www, and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS
Host_Alias,
jill may run any
commands in the directory /usr/bin/ except for those
commands belonging to the SU and
SHELLS
Cmnd_Aliases.
While not specifically mentioned in the rule, the commands in the
PAGERS Cmnd_Alias all reside in
/usr/bin and have the noexec
option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory /usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN
User_Alias (will, wendy, and wim), may run any command as
user www (which owns the web pages) or simply
su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\ /sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM Host_Alias (orion, perseus, hercules) without entering a password. This is a bit tedious for users to type, so it is a prime candidate for encapsulating in a shell script.
It is generally not effective to “subtract” commands
from ALL using the
‘!’ operator. A user can trivially
circumvent this by copying the desired command to a different name and then
executing that. For example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent
bill from running
the commands listed in SU or
SHELLS since he can simply copy those commands to a
different name, or use a shell escape from an editor or other program.
Therefore, these kind of restrictions should be considered advisory at best
(and reinforced by policy).
In general, if a user has sudo ALL there is
nothing to prevent them from creating their own program that gives them a
root shell (or making their own copy of a shell)
regardless of any ‘!’ elements in the
user specification.
If the fast_glob option is in use, it is not possible to reliably negate commands where the path name includes globbing (aka wildcard) characters. This is because the C library's fnmatch(3) function cannot resolve relative paths. While this is typically only an inconvenience for rules that grant privileges, it can result in a security issue for rules that subtract or revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run
‘/usr/bin/passwd root’ if
fast_glob is enabled by changing to
/usr/bin and running
‘./passwd root’ instead.
Another potential issue is that when sudo
executes the command, it must use the command or path specified by the user
instead of a path listed in the sudoers file. This may
lead to a time of check versus time of use race condition.
Command line arguments are matched as a single, concatenated
string. This mean a wildcard character such as
‘?’ or
‘*’ will match across word boundaries,
which may be unexpected. For example, while a sudoers entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. A safer alternative is to use a regular expression for matching command line arguments. The above example can be rewritten as a regular expression:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$
The regular expression will only match a single file with a name that begins with /var/log/messages and does not include any white space in the name. It is often better to do command line processing outside of the sudoers file in a scripting language for anything non-trivial.
Using a regular expression to match a command name has the same security implications as using the fast_glob option:
sudo executes the command, it must use the
command or path specified by the user instead of a path listed in the
sudoers file. This may lead to a time of check versus
time of use race condition.These issues do not apply to rules where only the command line options are matched using a regular expression.
Once sudo executes a program, that program
is free to do whatever it pleases, including run other programs. This can be
a security issue since it is not uncommon for a program to allow shell
escapes, which lets a user bypass sudo's access
control and logging. Common programs that permit shell escapes include
shells (obviously), editors, paginators, mail, and terminal programs.
There are four basic approaches to this problem:
sudoedit is a better solution to
running editors via sudo. Due to the large number
of programs that offer shell escapes, restricting users to the set of
programs that do not is often unworkable.sudo's
intercept functionality can be used to transparently
intercept an attempt to run a new command, allow or deny it based on
sudoers rules, and log the result. For example, this can
be used to restrict the commands run from within a privileged shell or
editor. However, not all programs operate correctly when
intercept is enabled.
There are two underlying mechanisms that may be used to implement intercept mode: dso and trace. The intercept_type setting can be used to select between them.
The first mechanism, dso, overrides the
standard C library functions that are used to execute a command. It does
this by setting an environment variable (usually
LD_PRELOAD) to the path of a dynamic shared
object, or shared library, containing custom versions of the
execve(2),
execl(3),
execle(3),
execlp(3),
execv(3),
execvp(3),
execvpe(3), and
system(3) library functions that
connect back to sudo for a policy decision.
Note, however, that this applies only to dynamically-linked executables.
It is not possible to intercept commands for statically-linked
executables or executables that run under binary emulation this way.
Because most dynamic loaders ignore LD_PRELOAD
(or the equivalent) when running set-user-ID and set-group-ID programs,
sudoers will not permit such programs to be run
in intercept mode by default. The
dso mechanism is incompatible with
sudo's SELinux RBAC support (but see below).
SELinux disables LD_PRELOAD by default and
interferes with file descriptor inheritance, which
sudo relies on.
The second mechanism, trace, is available on
Linux systems that support
seccomp(2) filtering. It uses
ptrace(2) and
seccomp(2) to intercept the
execve(2) system call instead of
pre-loading a dynamic shared object. Both static and dynamic executables
are supported and it is compatible with sudo's
SELinux RBAC mode. Functions utilizing the
execveat(2) system call, such as
fexecve(3), are not currently
intercepted. Programs that rely on
ptrace(2) themselves, such as
debuggers and system call tracers (such as
strace(1) and
truss(1)) will be unable to function
if intercept is enabled in trace
mode. This same restriction applies to the log_subcmds
sudoers option.
The intercept feature is known to work on
Solaris, *BSD, Linux, macOS, HP-UX 11.x and AIX 5.3 and above. It should
be supported on most operating systems that support the
LD_PRELOAD environment variable or an
equivalent. It is not possible to intercept shell built-in commands or
restrict the ability to read or write sensitive files from within a
shell.
To enable intercept mode on a per-command basis, use the
INTERCEPT tag as documented in the User
Specification section above. Here is that example again:
chuck research = INTERCEPT: ALL
This allows user chuck to run any command on
the machine “research” in intercept mode. Any commands run
via shell escapes will be validated and logged by
sudo. If you are unsure whether or not your
system is capable of supporting intercept, you can
always just try it out and check whether or not external commands run
via a shell are logged when intercept is enabled.
There is an inherent race condition
between when a command is checked against
sudoers rules and when it is actually executed.
If a user is allowed to run arbitrary commands, they may be able to
change the execve(2) arguments in the
program after the sudoers policy check has
completed but before the new command is executed. Starting with version
1.9.12, the trace method will verify that the command
and its arguments have not changed after
execve(2) has completed but before
execution of the new program has had a chance to run. This is not the
case with the dso method. See the description of the
intercept_verify
setting for more information.
sudo's noexec functionality can
be used to prevent a program run by sudo from
executing any other programs. On most systems, it uses the same
LD_PRELOAD mechanism as
intercept (see above) and thus the same caveats apply.
The noexec functionality is capable of blocking
execution of commands run via the
execve(2),
execl(3),
execle(3),
execlp(3),
exect(3),
execv(3),
execveat(3),
execvP(3),
execvp(3),
execvpe(3),
fexecve(3),
popen(3),
posix_spawn(3),
posix_spawnp(3),
system(3), and
wordexp(3) functions. On Linux, a
seccomp(2) filter is used to implement
noexec. On Solaris 10 and higher,
noexec uses Solaris privileges instead of the
LD_PRELOAD environment variable.
To enable noexec for a command, use the
NOEXEC tag as documented in the User
Specification section above. Here is that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi with noexec enabled. This will prevent those two commands from executing other commands (such as a shell). If you are unsure whether or not your system is capable of supporting noexec you can always just try it out and check whether shell escapes work when noexec is enabled.
Restricting shell escapes is not a panacea. Programs running as
root are still capable of many potentially hazardous
operations (such as changing or overwriting files) that could lead to
unintended privilege escalation. In the specific case of an editor, a safer
approach is to give the user permission to run
sudoedit (see below).
The sudoers plugin includes
sudoedit support which allows users to securely edit
files with the editor of their choice. As sudoedit
is a built-in command, it must be specified in the sudoers
file without a leading path. However, it may take command line arguments
just as a normal command does. Wildcards used in sudoedit
command line arguments are expected to be path names, so a forward slash
(‘/’) will not be matched by a
wildcard.
Unlike other sudo commands, the editor is
run with the permissions of the invoking user and with the environment
unmodified. More information may be found in the description of the
-e option in
sudo(8).
For example, to allow user operator to edit the “message of the day” file on any machine:
operator ALL = sudoedit /etc/motd
The operator user then runs sudoedit as
follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy of /etc/motd. After the file has been edited, /etc/motd will be updated with the contents of the temporary copy.
Users should never be
granted sudoedit permission to edit a file that
resides in a directory the user has write access to, either directly or via
a wildcard. If the user has write access to the directory it is possible to
replace the legitimate file with a link to another file, allowing the
editing of arbitrary files. To prevent this, starting with version 1.8.16,
symbolic links will not be followed in writable directories and
sudoedit will refuse to edit a file located in a
writable directory unless the
sudoedit_checkdir
option has been disabled or the invoking user is root.
Additionally, in version 1.8.15 and higher, sudoedit
will refuse to open a symbolic link unless either the
sudoedit_follow option is enabled or the
sudoedit command is prefixed with the
FOLLOW tag in the sudoers
file.
sudoers will check the ownership of its
time stamp directory (/run/sudo/ts by default) and
ignore the directory's contents if it is not owned by root
or if it is writable by a user other than root. Older
versions of sudo stored time stamp files in
/tmp; this is no longer recommended as it may be
possible for a user to create the time stamp themselves on systems that
allow unprivileged users to change the ownership of files they create.
While the time stamp directory
should be cleared
at reboot time, not all systems contain a /run or
/var/run directory. To avoid potential problems,
sudoers will ignore time stamp files that date from
before the machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow
unprivileged users to change the system clock. Since
sudoers relies on the system clock for time stamp
validation, it may be possible on such systems for a user to run
sudo for longer than
timestamp_timeout by setting the clock back. To combat
this, sudoers uses a monotonic clock (which never
moves backwards) for its time stamps if the system supports it.
sudoers will not honor time stamps set far
in the future. Time stamps with a date greater than current_time + 2 *
TIMEOUT will be ignored and
sudoers will log and complain.
If the timestamp_type option is set to “tty”, the time stamp record includes the device number of the terminal the user authenticated with. This provides per-terminal granularity but time stamp records may still outlive the user's session.
Unless the timestamp_type option is set to “global”, the time stamp record also includes the session ID of the process that last authenticated. This prevents processes in different terminal sessions from using the same time stamp record. On systems where a process's start time can be queried, the start time of the session leader is recorded in the time stamp record. If no terminal is present or the timestamp_type option is set to “ppid”, the start time of the parent process is used instead. In most cases this will prevent a time stamp record from being re-used without the user entering a password when logging out and back in again.
Versions 1.8.4 and higher of the sudoers
plugin support a flexible debugging framework that can help track down what
the plugin is doing internally if there is a problem. This can be configured
in the sudo.conf(5) file.
The sudoers plugin uses the
same debug flag format as the sudo front-end:
subsystem@priority.
The priorities used by sudoers,
in order of decreasing severity, are: crit,
err,
warn,
notice,
diag,
info, trace, and
debug. Each priority, when specified, also includes all
priorities higher than it. For example, a priority of
notice would include debug messages logged at
notice and higher.
The following subsystems are used by the
sudoers plugin:
sudoersFor example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5), sudo_plugin(5), sudoers.ldap(5), sudoers_timestamp(5), sudo(8), visudo(8)
Many people have worked on sudo over the
years; this version consists of code written primarily by:
See the CONTRIBUTORS.md file in the sudo
distribution (https://www.sudo.ws/about/contributors/) for an exhaustive
list of people who have contributed to sudo.
The sudoers file should
always
be edited by the visudo utility which locks the file
and checks for syntax errors. If sudoers contains syntax
errors, sudo may refuse to run, which is a serious
problem if sudo is your only method of obtaining
superuser privileges. Recent versions of sudoers
will attempt to recover after a syntax error by ignoring the rest of the
line after encountering an error. Older versions of
sudo will not run if sudoers
contains a syntax error.
When using netgroups of machines (as opposed to users), if you store fully qualified host name in the netgroup (as is usually the case), you either need to have the machine's host name be fully qualified as returned by the hostname command or use the fqdn option in sudoers.
If you believe you have found a bug in
sudo, you can submit a bug report at
https://bugzilla.sudo.ws/
Limited free support is available via the sudo-users mailing list, see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search the archives.
sudo is provided “AS IS” and
any express or implied warranties, including, but not limited to, the
implied warranties of merchantability and fitness for a particular purpose
are disclaimed. See the LICENSE.md file distributed with
sudo or https://www.sudo.ws/about/license/ for
complete details.
| November 6, 2023 | Sudo 1.9.15p4 |