xauth - X authority file utility
xauth [ -f authfile ] [ -vqibn ] [ command arg
The xauth program is used to edit and display the authorization
information used in connecting to the X server. This program is usually used
to extract authorization records from one machine and merge them in on another
(as is the case when using remote logins or granting access to other users).
Commands (described below) may be entered interactively, on the xauth
command line, or in scripts. Note that this program does not contact
the X server except when the generate command is used. Normally xauth
is not used to create the authority file entry in the first place; the program
that starts the X server (often xdm or startx) does that.
The following options may be used with xauth. They may be given
individually (e.g., -q -i) or may combined (e.g., -qi).
The following commands may be used to manipulate authority files:
- -f authfile
- This option specifies the name of the authority file to use. By default,
xauth will use the file specified by the XAUTHORITY environment
variable or .Xauthority in the user's home directory.
- This option indicates that xauth should operate quietly and not
print unsolicited status messages. This is the default if an xauth
command is given on the command line or if the standard output is not
directed to a terminal.
- This option indicates that xauth should operate verbosely and print
status messages indicating the results of various operations (e.g., how
many records have been read in or written out). This is the default if
xauth is reading commands from its standard input and its standard
output is directed to a terminal.
- This option indicates that xauth should ignore any authority file
locks. Normally, xauth will refuse to read or edit any authority
files that have been locked by other programs (usually xdm or
- This option indicates that xauth should attempt to break any
authority file locks before proceeding. Use this option only to clean up
- This option indicates that xauth should not attempt to resolve any
hostnames, but should simply always print the host address as stored in
the authority file.
- This option shows the version number of the xauth executable.
Display names for the add, [n]extract, [n]list,
[n]merge, and remove commands use the same format as the DISPLAY
environment variable and the common -display command line argument.
Display-specific information (such as the screen number) is unnecessary and
will be ignored. Same-machine connections (such as local-host sockets, shared
memory, and the Internet Protocol hostname localhost) are referred to
as hostname/unix:displaynumber so that local entries for
different machines may be stored in one authority file.
The most common use for xauth is to extract the entry for the current
display, copy it to another machine, and merge it into the user's authority
file on the remote machine:
- add displayname protocolname hexkey
- An authorization entry for the indicated display using the given protocol
and key data is added to the authorization file. The data is specified as
an even-lengthed string of hexadecimal digits, each pair representing one
octet. The first digit of each pair gives the most significant 4 bits of
the octet, and the second digit of the pair gives the least significant 4
bits. For example, a 32 character hexkey would represent a 128-bit value.
A protocol name consisting of just a single period is treated as an
abbreviation for MIT-MAGIC-COOKIE-1.
- generate displayname protocolname [trusted|untrusted]
- [timeout seconds] [group group-id] [data
This command is similar to add. The main difference is that
instead of requiring the user to supply the key data, it connects to the
server specified in displayname and uses the SECURITY extension
in order to get the key data to store in the authorization file. If the
server cannot be contacted or if it does not support the SECURITY
extension, the command fails. Otherwise, an authorization entry for the
indicated display using the given protocol is added to the authorization
file. A protocol name consisting of just a single period is treated as
an abbreviation for MIT-MAGIC-COOKIE-1.
If the trusted option is used, clients that connect
using this authorization will have full run of the display, as usual. If
untrusted is used, clients that connect using this authorization
will be considered untrusted and prevented from stealing or tampering
with data belonging to trusted clients. See the SECURITY extension
specification for full details on the restrictions imposed on untrusted
clients. The default is untrusted.
The timeout option specifies how long in seconds this
authorization will be valid. If the authorization remains unused (no
clients are connected with it) for longer than this time period, the
server purges the authorization, and future attempts to connect using it
will fail. Note that the purging done by the server does not
delete the authorization entry from the authorization file. The default
timeout is 60 seconds.
The group option specifies the application group that
clients connecting with this authorization should belong to. See the
application group extension specification for more details. The default
is to not belong to an application group.
The data option specifies data that the server should
use to generate the authorization. Note that this is not the same
data that gets written to the authorization file. The interpretation of
this data depends on the authorization protocol. The hexdata is
in the same format as the hexkey described in the add command.
The default is to send no data.
- [n]extract filename displayname...
- Authorization entries for each of the specified displays are written to
the indicated file. If the nextract command is used, the entries
are written in a numeric format suitable for non-binary transmission (such
as secure electronic mail). The extracted entries can be read back in
using the merge and nmerge commands. If the filename
consists of just a single dash, the entries will be written to the
- [n]list [displayname...]
- Authorization entries for each of the specified displays (or all if no
displays are named) are printed on the standard output. If the
nlist command is used, entries will be shown in the numeric format
used by the nextract command; otherwise, they are shown in a
textual format. Key data is always displayed in the hexadecimal format
given in the description of the add command.
- [n]merge [filename...]
- Authorization entries are read from the specified files and are merged
into the authorization database, superseding any matching existing
entries. If the nmerge command is used, the numeric format given in
the description of the extract command is used. If a filename
consists of just a single dash, the standard input will be read if it
hasn't been read before.
- remove displayname...
- Authorization entries matching the specified displays are removed from the
- source filename
- The specified file is treated as a script containing xauth commands
to execute. Blank lines and lines beginning with a sharp sign (#) are
ignored. A single dash may be used to indicate the standard input, if it
hasn't already been read.
- Information describing the authorization file, whether or not any changes
have been made, and from where xauth commands are being read is
printed on the standard output.
- If any modifications have been made, the authority file is written out (if
allowed), and the program exits. An end of file is treated as an implicit
- The program exits, ignoring any modifications. This may also be
accomplished by pressing the interrupt character.
- This command shows the version number of the xauth executable.
- help [string]
- A description of all commands that begin with the given string (or all
commands if no string is given) is printed on the standard output.
- A short list of the valid commands is printed on the standard output.
% xauth extract - $DISPLAY | ssh otherhost xauth merge -
The following command contacts the server :0 to create an
authorization using the MIT-MAGIC-COOKIE-1 protocol. Clients that connect
with this authorization will be untrusted.
% xauth generate :0 .
This xauth program uses the following environment variables:
- to get the name of the authority file to use if the -f option isn't
- to get the user's home directory if XAUTHORITY isn't defined.
X(7), Xsecurity(7), xhost(1), Xserver(1), xdm(1), startx(1), Xau(3).
Users that have unsecure networks should take care to use encrypted file
transfer mechanisms to copy authorization entries between machines. Similarly,
the MIT-MAGIC-COOKIE-1 protocol is not very useful in unsecure
environments. Sites that are interested in additional security may need to use
encrypted authorization mechanisms such as Kerberos.
- default authority file if XAUTHORITY isn't defined.
Spaces are currently not allowed in the protocol name. Quoting
could be added for the truly perverse.
Jim Fulton, MIT X Consortium