General

-e expr

Modifies which events to trace or how to trace them by specifying a qualifying expression. The format of the expression is:

where qualifier is one of trace (or t), trace-fds (or trace-fd or fd or fds), abbrev (or a), verbose (or v), raw (or x), signal (or signals or s), read (or reads or r), write (or writes or w), fault, inject, status, quiet (or silent or silence or q), decode-fds (or decode-fd), decode-pids (or decode-pid), or kvm, and value is a qualifier-dependent symbol or number. The default qualifier is trace. Using an exclamation mark negates the set of values. For example, -e open is equivalent to -e trace=open, which in turn means trace only the open system call. By contrast, -e trace=!open means to trace every system call except open. In addition, the special values all and none may be used to trace every event or no events, respectively.

Note that some shells use the exclamation mark for history expansion even inside quoted arguments. In that case, the exclamation mark must be escaped with a backslash.

Startup

-E var=val

--env=var=val

Runs the command with the environment variable var=val set for execution.

-E var

--env=var

Removes var from the inherited environment variables before executing the command.

-p pid

--attach=pid

Attaches to the process with the process ID pid and begin tracing. The trace may be terminated at any time by a keyboard interrupt signal (CTRL-C). strace will respond by detaching itself from the traced processes, leaving them to continue running.

Multiple -p options can be used to attach to several processes in addition to the command, which is optional if at least one -p option is given.

A single -p option can accept multiple process IDs separated by a comma (“,”), space (“ ”), tab, or newline. Consequently, syntaxes like -p "$(pidof PROG)" and -p "$(pgrep PROG)" are supported.

-u username

--user=username

Runs command with the user ID, group ID, and supplementary groups of username. This option is only useful when running as root, as it enables the correct execution of setuid and/or setgid binaries. Unless this option is used, setuid and setgid programs are executed without their effective privileges.

-u UID:GID

--user=UID:GID

Alternative syntax where the program is started with exactly the given user and group IDs, and an empty list of supplementary groups. In this case, user and group name lookups are not performed.

--argv0=name

Sets the executed command's argv[0] to name. This is useful for tracing multi-call executables that interpret argv[0], such as busybox or kmod.

Tracing

-b syscall

--detach-on=syscall

Detaches from the traced process if the specified system call is reached. Currently, only execve keyword is supported, which includes execve(2) and execveat(2) system calls. This option is useful for tracing a multi-threaded process with -f without also tracing its (potentially very complex) child processes.

-D

--daemonize

--daemonize=grandchild

Runs the tracer process as a grandchild of the tracee, not as its parent. This reduces the visible effect of strace by keeping the tracee a direct child of the calling process.

-DD

--daemonize=pgroup

--daemonize=pgrp

Runs tracer process as tracee's grandchild in a separate process group. In addition to reducing the visible effect of strace, this also prevents strace from being terminated by a kill(2) signal sent to the entire process group.

-DDD

--daemonize=session

Runs the tracer process as the tracee's grandchild in a separate session (known as "true daemonisation"). In addition to reduction of the visible effect of strace, this also prevents strace from being terminated upon session termination.

-f

--follow-forks

Traces child processes as they are created by currently traced processes as a result of the fork(2), vfork(2) and clone(2) system calls. Note that if process PID is multi-threaded, using -f -p PID attaches to all of its threads, not just the one with thread_id = PID.

--output-separately

If the --output=filename option is in effect, the trace for each process is written to a separate filename.pid file, where pid is the process ID.

-ff

--follow-forks --output-separately

Combines the effects of --follow-forks and --output-separately options. This is incompatible with -c, since no per-process counts are kept.

Use strace-log-merge(1) to get a combined view of the log files.

-I interruptible

--interruptible=interruptible

Controls when strace can be interrupted by signals (such as pressing CTRL-C).

--syscall-limit=limit

Detaches all tracees after limit system calls have been captured. System calls filtered out via --trace, --trace-path or --status options are not considered when keeping track of the number of system calls that are captured.

--kill-on-exit

Applies the PTRACE_O_EXITKILL ptrace option to all tracees, which sends a SIGKILL signal to a tracee if the tracer exits. This prevents tracees from being left running after the tracer exits, as they will not be detached on cleanup. --kill-on-exit is not compatible with -p/--attach options.

Filtering

-e trace=syscall_set

-e t=syscall_set

--trace=syscall_set

Traces only the specified set of system calls. syscall_set is defined as [!]value[,value], and value can be one of the following:

The -c option is useful for determining which system calls might be useful to trace. For example, --trace=open,close,read,write means to only trace those four system calls. Be careful when making inferences about the user/kernel boundary if only a subset of system calls are being monitored. The default is --trace=all.

-e trace-fd=set

-e trace-fds=set

-e fd=set

-e fds=set

--trace-fds=set

Traces only the system calls that operate on the specified subset of (non-negative) file descriptors. Note that usage of this option also filters out all the system calls that do not operate on file descriptors at all.

This filter is combined with the --trace-path filter; a system call is traced if it matches either of them.

-e signal=set

-e signals=set

-e s=set

--signal=set

Traces only the specified subset of signals. The default is --signal=all. For example, --signal=!SIGIO (or --signal=!io) causes SIGIO signals not to be traced.

-e status=set

--status=set

Prints only system calls with the specified return status. The default is --status=all. When using the status qualifier, the chronological order of events may not be preserved. This is because strace must wait for a system call to complete before deciding whether to print it. If two system calls are executed by concurrent threads, strace will first print both the entry and exit of the first system call to exit, regardless of their respective entry time. The entry and exit of the second system call to exit will be printed afterwards. Here is an example when select(2) is called, but a different thread calls clock_gettime(2) before select(2) finishes:

[pid 28779] 1130322148.939977 clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
[pid 28772] 1130322148.438139 select(4, [3], NULL, NULL, NULL) = 1 (in [3])
    

set can include the following elements:

-P path

--trace-path=path

Traces only system calls accessing path. Multiple -P options can be used to specify several paths. This filter is combined with the --trace-fds filter; a system call is traced if it matches either option.

-z

--successful-only

Prints only system calls that returned without an error code.

-Z

--failed-only

Prints only system calls that returned with an error code.

Output format

-a column

--columns=column

Aligns return values in a specific column (default column 40).

-e abbrev=syscall_set

-e a=syscall_set

--abbrev=syscall_set

Abbreviates the output from printing each member of large structures. The syntax of the syscall_set specification is the same as in the --trace option. The default is --abbrev=all. The -v option has the effect of --abbrev=none.

-e verbose=syscall_set

-e v=syscall_set

--verbose=syscall_set

Dereferences structures for the specified set of system calls. The syntax of the syscall_set specification is the same as in the --trace option. The default is --verbose=all.

-e raw=syscall_set

-e x=syscall_set

--raw=syscall_set

Prints raw, undecoded arguments for the specified set of system calls. The syntax of the syscall_set specification is the same as in the --trace option. This option has the effect of causing all arguments to be printed in hexadecimal. This option is useful if the decoding is not trusted, or if the actual numeric value of an argument is needed. See also -X raw option.

-e read=set

-e reads=set

-e r=set

--read=set

Performs a full hexadecimal and ASCII dump of all the data read from file descriptors listed in the specified set. For example, to see all input activity on file descriptors 3 and 5 use --read=3,5. Note that this is independent from the normal tracing of the read(2) system call that is controlled by the option --trace=read.

-e write=set

-e writes=set

-e w=set

--write=set

Performs a full hexadecimal and ASCII dump of all the data written to file descriptors listed in the specified set. For example, to see all output activity on file descriptors 3 and 5 use --write=3,5. Note that this is independent from the normal tracing of the write(2) system call that is controlled by the option --trace=write.

-e quiet=set

-e silent=set

-e silence=set

-e q=set

--quiet=set

--silent=set

--silence=set

Suppresses various information messages. The default is --quiet=none. set can include the following elements:

-e decode-fds=set

--decode-fds=set

Decodes various information associated with file descriptors. The default is --decode-fds=none. set can include the following elements:

-e decode-pids=set

--decode-pids=set

Decodes various information associated with process IDs (and also thread IDs, process group IDs, and session IDs). The default is --decode-pids=none. set can include the following elements:

-e kvm=vcpu

--kvm=vcpu

Prints the exit reason of kvm vcpu. Requires Linux kernel version 4.16.0 or higher.

-e namespace=new

--namespace=new

Prints the new namespaces entered by the tracee. The following system calls are supported: clone(2), clone3(2), setns(2), and unshare(2).

-i

--instruction-pointer

Prints the instruction pointer at the time of the system call.

-n

--syscall-number

Prints the system call number.

-N

--arg-names

Prints the system call argument names.

-k

--stack-trace[=symbol]

Prints the execution stack trace of the traced processes after each system call.

--stack-trace-frame-limit=limit

Prints no more than this amount of stack trace frames when backtracing a system call (the default is 256). Use this option with the --stack-trace (or -k) option.

-o filename

--output=filename

Writes the trace output to the file filename rather than to stderr. filename.pid form is used if -ff option is supplied. If the argument begins with '|' or '!', the rest of the argument is treated as a command and all output is piped to it. This is convenient for piping the debugging output to a program without affecting the redirections of executed programs. Piping output to a command is not currently compatible with the -ff option.

-A

--output-append-mode

Opens the file provided in the -o option in append mode.

-q

--quiet

--quiet=attach,personality

Suppresses messages about attaching, detaching, and personality changes. This happens automatically when output is redirected to a file and the command is run directly instead of attaching.

-qq

--quiet=attach,personality,exit

Suppresses messages about attaching, detaching, personality changes, and process exit status.

-qqq

--quiet=all

Suppresses all suppressible messages (please refer to the --quiet option description for the full list of suppressible messages).

-r

--relative-timestamps[=precision]

Prints a relative timestamp upon entry to each system call. This records the time difference between the beginning of successive system calls. precision can be one of s (for seconds), ms (milliseconds), us (microseconds), or ns (nanoseconds), and allows setting the precision of time value being printed. Default is us (microseconds). Note that because the -r option uses the monotonic clock, its measurements may differ from the time differences reported by the -t option, which uses the wall clock.

-s strsize

--string-limit=strsize

Specifies the maximum string size to print (the default is 32). Note that filenames are not considered strings and are always printed in full.

--absolute-timestamps[=[[format:]format],[[precision:]precision]]

--timestamps[=[[format:]format],[[precision:]precision]]

Prefixes each line of the trace with the wall clock time in the specified format with the specified precision. format can be one of the following:

precision can be one of s (for seconds), ms (milliseconds), us (microseconds), or ns (nanoseconds). Default arguments for the option are format:time,precision:s.

-t

--absolute-timestamps

Prefixes each line of the trace with the wall clock time.

-tt

--absolute-timestamps=precision:us

Prints the wall clock time with microsecond precision.

-ttt

--absolute-timestamps=format:unix,precision:us

Prints the wall clock time as seconds since the epoch, with microsecond precision.

-T

--syscall-times[=precision]

Shows the time spent in system calls. This records the time difference between the beginning and the end of each system call. precision can be one of s (for seconds), ms (milliseconds), us (microseconds), or ns (nanoseconds), and allows setting the precision of time value being printed. Default is us (microseconds).

-v

--no-abbrev

Prints unabbreviated versions of environment, stat, termios, etc. calls. These structures are very common, so the default behavior is to display a reasonable subset of their members. Use this option to see all members in full detail.

--strings-in-hex[=option]

Controls the use of hexadecimal escape sequences when printing strings. This option alters the default escaping behavior.

Normally (when neither this option nor -x is used), strace introduces escape sequences in two situations: to represent non-printable and non-ASCII characters (i.e., those with character codes less than 32 or greater than 127), or to disambiguate output, for example, by escaping the quotation marks that enclose a string or the angle brackets used in file descriptor paths. When a character must be escaped, strace prioritizes symbolic C-standard sequences if one exists: “\t” (tab), “\n” (newline), “\v” (vertical tab), “\f” (form feed), and “\r” (carriage return). For all other characters that require escaping, strace defaults to using an octal representation of the character's byte value. This option allows you to override this default behavior and use hexadecimal escapes instead of octal ones.

option can be one of the following:

When the option is supplied without an argument, all is assumed.

-x

--strings-in-hex=non-ascii

Prints all non-ASCII strings in hexadecimal string format.

-xx

--strings-in-hex[=all]

Prints all strings in hexadecimal string format.

-X format

--const-print-style=format

Sets the format for printing of named constants and flags. Supported format values are:

-y

--decode-fds

--decode-fds=path

Prints paths associated with file descriptor arguments and with the AT_FDCWD constant.

-yy

--decode-fds=all

Prints all available information associated with file descriptors: protocol-specific information associated with socket file descriptors, block/character device number associated with device file descriptors, and PIDs associated with pidfd file descriptors.

--pidns-translation

--decode-pids=pidns

If strace and tracee are in different PID namespaces, print PIDs in strace's namespace, too.

-Y

--decode-pids=comm

Prints command names for PIDs.

--always-show-pid

Shows PID prefix also for the process started by strace. Implied when -f and -o are both specified.

Statistics

-c

--summary-only

Counts time, calls, and errors for each system call and report a summary on program exit, suppressing the regular output. This shows system time (CPU time spent in the kernel), which is independent of wall clock time. If -c is used with -f, only aggregate totals for all traced processes are kept.

-C

--summary

Like -c, but also prints the regular output while processes are running.

-O overhead

--summary-syscall-overhead=overhead

Sets the overhead for tracing system calls to overhead. This is useful for overriding the default heuristic, which estimates the time spent in the measurement process itself when timing system calls with the -c option. The accuracy of the heuristic can be gauged by timing a given program run without tracing (using time(1)) and comparing the accumulated system call time to the total produced using -c.

The format of overhead specification is described in section Time specification format description.

-S sortby

--summary-sort-by=sortby

Sorts the output of the histogram printed by the -c option by the specified criterion. Valid values are time (or time-percent or time-total or total-time), min-time (or shortest or time-min), max-time (or longest or time-max), avg-time (or time-avg), calls (or count), errors (or error), name (or syscall or syscall-name), and nothing (or none); default is time.

-U columns

--summary-columns=columns

Configures the set and order of columns shown in the call summary. The columns argument is a comma-separated list containing one or more of the following values:

The default value is time-percent,total-time,avg-time,calls,errors,name. If the name field is not supplied explicitly, it is added as the last column.

-w

--summary-wall-clock

Summarizes the wall clock time for each system call, measured from its beginning to its end. The default is to summarize the system time.

Tampering

--inject=syscall_set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_enter=delay][:delay_exit=delay][:poke_enter=@argN=DATAN,@argM=DATAM...][:poke_exit=@argN=DATAN,@argM=DATAM...][:when=expr]

Performs system call tampering for the specified set of system calls.

The syntax of the syscall_set specification is the same as in the --trace option.

At least one of error, retval, signal, delay_enter, delay_exit, poke_enter, or poke_exit action options must be specified. error and retval are mutually exclusive.

If the error=errno option is specified, a fault is injected into the system call. This is achieved by replacing the system call number with -1 (representing an invalid system call) and setting the error code to the specified errno. This behavior of replacing the syscall number with -1 can be overridden using the syscall= option. The errno can be a symbolic name like ENOSYS or a numeric value in the range 1..4095.

If the retval=value option is specified, a success value is injected. The system call number is replaced as with the error= option, but instead of an error, the specified success value is returned to the caller process.

If the signal=sig option is specified with either a symbolic value like SIGSEGV or a numeric value within 1..SIGRTMAX range, that signal is delivered on entering every system call specified by the syscall_set.

If the delay_enter=delay or delay_exit=delay options are specified, delay injection is performed: the tracee is delayed by time period specified by delay on entering or exiting the system call, respectively. The format of delay specification is described in section Time specification format description.

If the poke_enter=@argN=DATAN,@argM=DATAM... or poke_exit=@argN=DATAN,@argM=DATAM... options are specified, tracee's memory at locations, pointed to by system call arguments argN and argM (going from arg1 to arg7) is overwritten by data DATAN and DATAM (specified in hexadecimal format; for example poke_enter=@arg1=0000DEAD0000BEEF). The poke_enter option modifies memory on system call enter, while poke_exit does so on system call exit.

The injection actions are independent. For example, specifying only signal= delivers a signal without altering the system call's outcome or delaying it. Similarly, specifying only error= injects a system call fault without adding a signal or delay.

If the signal=sig option is specified together with error=errno or retval=value, then both injection of a fault or success and signal delivery are performed.

If the syscall=syscall option is specified, the given syscall is injected instead of the default -1. The specified syscall must have no side effects; currently, only system calls from the %pure set are supported.

Unless the when=expr subexpression is specified, an injection is being made into every invocation of each system call from the syscall_set.

The format of the subexpression is:

Number first stands for the first invocation number in the range, number last stands for the last invocation number in the range, and step stands for the step between two consecutive invocations. The following combinations are useful:

For example, to fail each third and subsequent chdir system calls with ENOENT, use --inject=chdir:error=ENOENT:when=3+.

The valid range for numbers first and step is 1..65535, and for number last is 1..65534.

An injection expression can contain at most one fault or return value specification (i.e., either error= or retval=) and at most one signal= specification. If an injection expression contains multiple when= specifications, the last one takes precedence.

Accounting of system calls that are subject to injection is done per system call and per tracee.

Specification of system call injection can be combined with other system call filtering options, for example, -P /dev/urandom --inject=file:error=ENOENT.

-e inject=args

This is equivalent to --inject=args.

--fault=syscall_set[:error=errno][:when=expr]

Performs system call fault injection for the specified set of system calls.

This is a shortcut for the more general --inject= option, using a default errno of ENOSYS.

-e fault=args

This is equivalent to --fault=args.

Miscellaneous

-d

--debug

Shows some debugging output of strace itself on the standard error.

-F

This option is deprecated. It is retained for backward compatibility only and may be removed in future releases. Using multiple -F options is equivalent to a single -f. This option is ignored entirely if used in conjunction with one or more -f options.

-h

--help

Prints the help summary.

--seccomp-bpf

Attempts to use seccomp-bpf (see seccomp(2)) to cause the kernel to stop the tracee only for the system calls that are being traced.

This option has no effect unless -f/--follow-forks is also specified. --seccomp-bpf is not compatible with --syscall-limit and -b/--detach-on options. It is also not applicable to processes attached using -p/--attach option.

An attempt to enable system calls filtering using seccomp-bpf may fail for various reasons, e.g. there are too many system calls to filter, the seccomp API is not available, or strace itself is being traced. If the seccomp-bpf filter setup fails, strace proceeds as usual, stopping traced processes on every system call.

When --seccomp-bpf is activated and -p/--attach option is not used, --kill-on-exit option is activated as well.

Note that in cases when the tracee has another seccomp filter that returns an action value with a precedence greater than SECCOMP_RET_TRACE, strace --seccomp-bpf will not be notified. That is, if another seccomp filter, for example, disables the system call or kills the tracee, then strace --seccomp-bpf will not be aware of that system call invocation at all.

--tips[=[[id:]id],[[format:]format]]

Shows strace tips, tricks, and tweaks before exit. The id can be a non-negative integer to print a specific tip (note: these IDs are not guaranteed to be stable). It can also be random (the default), in which case a random tip is printed. format can be one of the following:

Default is id:random,format:compact.

-V

--version

Prints the version number of strace and the list of enabled optional features. Multiple instances of this option beyond specific threshold tend to increase der Strauss awareness.

Time specification format description

Time values are specified as a decimal floating point number (in a format accepted by strtod(3)), optionally followed by a suffix to indicate the unit of time: s (seconds), ms (milliseconds), us (microseconds), or ns (nanoseconds). If no suffix is specified, the value defaults to microseconds.

The described format is used for -O, --inject=delay_enter, and --inject=delay_exit options.