strace

STRACE(1)                    General Commands Manual                   STRACE(1)



NAME
       strace - trace system calls and signals

SYNOPSIS
       strace [-ACdffhikqqrtttTvVwxxyyzZ] [-I n] [-b execve] [-e expr]...
              [-O overhead] [-S sortby] [-U columns] [-a column] [-o file]
              [-s strsize] [-X format] [-P path]... [-p pid]... [--seccomp-bpf]
              { -p pid | [-DDD] [-E var[=val]]... [-u username] command [args] }

       strace -c [-dfwzZ] [-I n] [-b execve] [-e expr]... [-O overhead]
              [-S sortby] [-U columns] [-P path]... [-p pid]... [--seccomp-bpf]
              { -p pid | [-DDD] [-E var[=val]]... [-u username] command [args] }

DESCRIPTION
       In the simplest case strace runs the specified command until it exits.
       It intercepts and records the system calls which are called by a process
       and the signals which are received by a process.  The name of each system
       call, its arguments and its return value are printed on standard error or
       to the file specified with the -o option.

       strace is a useful diagnostic, instructional, and debugging tool.  System
       administrators, diagnosticians and trouble-shooters will find it
       invaluable for solving problems with programs for which the source is not
       readily available since they do not need to be recompiled in order to
       trace them.  Students, hackers and the overly-curious will find that a
       great deal can be learned about a system and its system calls by tracing
       even ordinary programs.  And programmers will find that since system
       calls and signals are events that happen at the user/kernel interface, a
       close examination of this boundary is very useful for bug isolation,
       sanity checking and attempting to capture race conditions.

       Each line in the trace contains the system call name, followed by its
       arguments in parentheses and its return value.  An example from stracing
       the command "cat /dev/null" is:

           open("/dev/null", O_RDONLY) = 3

       Errors (typically a return value of -1) have the errno symbol and error
       string appended.

           open("/foo/bar", O_RDONLY) = -1 ENOENT (No such file or directory)

       Signals are printed as signal symbol and decoded siginfo structure.  An
       excerpt from stracing and interrupting the command "sleep 666" is:

           sigsuspend([] <unfinished ...>
           --- SIGINT {si_signo=SIGINT, si_code=SI_USER, si_pid=...} ---
           +++ killed by SIGINT +++

       If a system call is being executed and meanwhile another one is being
       called from a different thread/process then strace will try to preserve
       the order of those events and mark the ongoing call as being unfinished.
       When the call returns it will be marked as resumed.

           [pid 28772] select(4, [3], NULL, NULL, NULL <unfinished ...>
           [pid 28779] clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
           [pid 28772] <... select resumed> )      = 1 (in [3])

       Interruption of a (restartable) system call by a signal delivery is
       processed differently as kernel terminates the system call and also
       arranges its immediate reexecution after the signal handler completes.

           read(0, 0x7ffff72cf5cf, 1)              = ? ERESTARTSYS (To be restarted)
           --- SIGALRM ... ---
           rt_sigreturn(0xe)                       = 0
           read(0, "", 1)                          = 0

       Arguments are printed in symbolic form with passion.  This example shows
       the shell performing ">>xyzzy" output redirection:

           open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3

       Here, the second and the third argument of open(2) are decoded by
       breaking down the flag argument into its three bitwise-OR constituents
       and printing the mode value in octal by tradition.  Where the traditional
       or native usage differs from ANSI or POSIX, the latter forms are
       preferred.  In some cases, strace output is proven to be more readable
       than the source.

       Structure pointers are dereferenced and the members are displayed as
       appropriate.  In most cases, arguments are formatted in the most C-like
       fashion possible.  For example, the essence of the command "ls -l
       /dev/null" is captured as:

           lstat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x3), ...}) = 0

       Notice how the 'struct stat' argument is dereferenced and how each member
       is displayed symbolically.  In particular, observe how the st_mode member
       is carefully decoded into a bitwise-OR of symbolic and numeric values.
       Also notice in this example that the first argument to lstat(2) is an
       input to the system call and the second argument is an output.  Since
       output arguments are not modified if the system call fails, arguments may
       not always be dereferenced.  For example, retrying the "ls -l" example
       with a non-existent file produces the following line:

           lstat("/foo/bar", 0xb004) = -1 ENOENT (No such file or directory)

       In this case the porch light is on but nobody is home.

       Syscalls unknown to strace are printed raw, with the unknown system call
       number printed in hexadecimal form and prefixed with "syscall_":

           syscall_0xbad(0x1, 0x2, 0x3, 0x4, 0x5, 0x6) = -1 ENOSYS (Function not implemented)


       Character pointers are dereferenced and printed as C strings.  Non-
       printing characters in strings are normally represented by ordinary C
       escape codes.  Only the first strsize (32 by default) bytes of strings
       are printed; longer strings have an ellipsis appended following the
       closing quote.  Here is a line from "ls -l" where the getpwuid(3) library
       routine is reading the password file:

           read(3, "root::0:0:System Administrator:/"..., 1024) = 422

       While structures are annotated using curly braces, simple pointers and
       arrays are printed using square brackets with commas separating elements.
       Here is an example from the command id(1) on a system with supplementary
       group ids:

           getgroups(32, [100, 0]) = 2

       On the other hand, bit-sets are also shown using square brackets, but set
       elements are separated only by a space.  Here is the shell, preparing to
       execute an external command:

           sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0

       Here, the second argument is a bit-set of two signals, SIGCHLD and
       SIGTTOU.  In some cases, the bit-set is so full that printing out the
       unset elements is more valuable.  In that case, the bit-set is prefixed
       by a tilde like this:

           sigprocmask(SIG_UNBLOCK, ~[], NULL) = 0

       Here, the second argument represents the full set of all signals.

OPTIONS
   General
       -e expr     A qualifying expression which modifies which events to trace
                   or how to trace them.  The format of the expression is:

                             [qualifier=][!]value[,value]...

                   where qualifier is one of trace (or t), 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), 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 means literally -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 have the obvious meanings.

                   Note that some shells use the exclamation point for history
                   expansion even inside quoted arguments.  If so, you must
                   escape the exclamation point with a backslash.

   Startup
       -E var=val
       --env=var=val
                   Run command with var=val in its list of environment
                   variables.

       -E var
       --env=var   Remove var from the inherited list of environment variables
                   before passing it on to the command.

       -p pid
       --attach=pid
                   Attach 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 process(es) leaving it
                   (them) to continue running.  Multiple -p options can be used
                   to attach to many processes in addition to command (which is
                   optional if at least one -p option is given).  -p "`pidof
                   PROG`" syntax is supported.

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

   Tracing
       -b syscall
       --detach-on=syscall
                   If specified syscall is reached, detach from traced process.
                   Currently, only execve(2) syscall is supported.  This option
                   is useful if you want to trace multi-threaded process and
                   therefore require -f, but don't want to trace its
                   (potentially very complex) children.

       -D
       --daemonize
       --daemonize=grandchild
                   Run tracer process as a grandchild, not as the parent of the
                   tracee.  This reduces the visible effect of strace by keeping
                   the tracee a direct child of the calling process.

       -DD
       --daemonize=pgroup
       --daemonize=pgrp
                   Run tracer process as tracee's grandchild in a separate
                   process group.  In addition to reduction of the visible
                   effect of strace, it also avoids killing of strace with
                   kill(2) issued to the whole process group.

       -DDD
       --daemonize=session
                   Run tracer process as tracee's grandchild in a separate
                   session ("true daemonisation").  In addition to reduction of
                   the visible effect of strace, it also avoids killing of
                   strace upon session termination.

       -f
       --follow-forks
                   Trace 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 -p PID -f will attach all threads of
                   process PID if it is multi-threaded, not only thread with
                   thread_id = PID.

       --output-separately
                   If the --output=filename option is in effect, each processes
                   trace is written to filename.pid where pid is the numeric
                   process id of each process.

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

                   One might want to consider using strace-log-merge(1) to
                   obtain a combined strace log view.

       -I interruptible
       --interruptible=interruptible
                   When strace can be interrupted by signals (such as pressing
                   CTRL-C).

                   1, anywhere    no signals are blocked;
                   2, waiting     fatal signals are blocked while decoding
                                  syscall (default);
                   3, never       fatal signals are always blocked (default if
                                  -o FILE PROG);
                   4, never_tstp  fatal signals and SIGTSTP (CTRL-Z) are always
                                  blocked (useful to make strace -o FILE PROG
                                  not stop on CTRL-Z, default if -D).

   Filtering
       -e trace=syscall_set
       --trace=syscall_set
                   Trace only the specified set of system calls.  syscall_set is
                   defined as [!]value[,value], and value can be one of the
                   following:

                   syscall      Trace specific syscall, specified by its name
                                (but see NOTES).

                   ?value       Question mark before the syscall qualification
                                allows suppression of error in case no syscalls
                                matched the qualification provided.

                   /regex       Trace only those system calls that match the
                                regex.  You can use POSIX Extended Regular
                                Expression syntax (see regex(7)).

                   syscall@64   Trace syscall only for the 64-bit personality.

                   syscall@32   Trace syscall only for the 32-bit personality.

                   syscall@x32  Trace syscall only for the 32-on-64-bit
                                personality.

                   %file
                   file         Trace all system calls which take a file name as
                                an argument.  You can think of this as an
                                abbreviation for
                                -e trace=open,stat,chmod,unlink,...  which is
                                useful to seeing what files the process is
                                referencing.  Furthermore, using the
                                abbreviation will ensure that you don't
                                accidentally forget to include a call like
                                lstat(2) in the list.  Betchya woulda forgot
                                that one.  The syntax without a preceding
                                percent sign ("-e trace=file") is deprecated.

                   %process
                   process      Trace system calls associated with process
                                lifecycle (creation, exec, termination).  The
                                syntax without a preceding percent sign ("-e
                                trace=process") is deprecated.

                   %net
                   %network
                   network      Trace all the network related system calls.  The
                                syntax without a preceding percent sign ("-e
                                trace=network") is deprecated.

                   %signal
                   signal       Trace all signal related system calls.  The
                                syntax without a preceding percent sign ("-e
                                trace=signal") is deprecated.

                   %ipc
                   ipc          Trace all IPC related system calls.  The syntax
                                without a preceding percent sign ("-e
                                trace=ipc") is deprecated.

                   %desc
                   desc         Trace all file descriptor related system calls.
                                The syntax without a preceding percent sign ("-e
                                trace=desc") is deprecated.

                   %memory
                   memory       Trace all memory mapping related system calls.
                                The syntax without a preceding percent sign ("-e
                                trace=memory") is deprecated.

                   %creds       Trace system calls that read or modify user and
                                group identifiers or capability sets.

                   %stat        Trace stat syscall variants.

                   %lstat       Trace lstat syscall variants.

                   %fstat       Trace fstat, fstatat, and statx syscall
                                variants.

                   %%stat       Trace syscalls used for requesting file status
                                (stat, lstat, fstat, fstatat, statx, and their
                                variants).

                   %statfs      Trace statfs, statfs64, statvfs, osf_statfs, and
                                osf_statfs64 system calls.  The same effect can
                                be achieved with -e trace=/^(.*_)?statv?fs
                                regular expression.

                   %fstatfs     Trace fstatfs, fstatfs64, fstatvfs, osf_fstatfs,
                                and osf_fstatfs64 system calls.  The same effect
                                can be achieved with -e trace=/fstatv?fs regular
                                expression.

                   %%statfs     Trace syscalls related to file system statistics
                                (statfs-like, fstatfs-like, and ustat).  The
                                same effect can be achieved with
                                -e trace=/statv?fs|fsstat|ustat regular
                                expression.

                   %clock       Trace system calls that read or modify system
                                clocks.

                   %pure        Trace syscalls that always succeed and have no
                                arguments.  Currently, this list includes
                                arc_gettls(2), getdtablesize(2), getegid(2),
                                getegid32(2), geteuid(2), geteuid32(2),
                                getgid(2), getgid32(2), getpagesize(2),
                                getpgrp(2), getpid(2), getppid(2),
                                get_thread_area(2) (on architectures other than
                                x86), gettid(2), get_tls(2), getuid(2),
                                getuid32(2), getxgid(2), getxpid(2), getxuid(2),
                                kern_features(2), and metag_get_tls(2) syscalls.

                   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 signal=set
       --signal=set
                   Trace 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
                   Print only system calls with the specified return status.
                   The default is status=all.  When using the status qualifier,
                   because strace waits for system calls to return before
                   deciding whether they should be printed or not, the
                   traditional order of events may not be preserved anymore.  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:

                   successful   Trace system calls that returned without an
                                error code.  The -z option has the effect of
                                status=successful.
                   failed       Trace system calls that returned with an error
                                code.  The -Z option has the effect of
                                status=failed.
                   unfinished   Trace system calls that did not return.  This
                                might happen, for example, due to an execve call
                                in a neighbour thread.
                   unavailable  Trace system calls that returned but strace
                                failed to fetch the error status.
                   detached     Trace system calls for which strace detached
                                before the return.

       -P path
       --trace-path=path
                   Trace only system calls accessing path.  Multiple -P options
                   can be used to specify several paths.

       -z
       --successful-only
                   Print only syscalls that returned without an error code.

       -Z
       --failed-only
                   Print only syscalls that returned with an error code.

   Output format
       -a column
       --columns=column
                   Align return values in a specific column (default column 40).

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

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

       -e raw=syscall_set
       --raw=syscall_set
                   Print raw, undecoded arguments for the specified set of
                   system calls.  The syntax of the syscall_set specification is
                   the same as in the -e trace option.  This option has the
                   effect of causing all arguments to be printed in hexadecimal.
                   This is mostly useful if you don't trust the decoding or you
                   need to know the actual numeric value of an argument.  See
                   also -X raw option.

       -e read=set
       --read=set  Perform 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 -e read=3,5.  Note that this is independent from the
                   normal tracing of the read(2) system call which is controlled
                   by the option -e trace=read.

       -e write=set
       --write=set Perform 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 -e write=3,5.  Note that this is independent from the
                   normal tracing of the write(2) system call which is
                   controlled by the option -e trace=write.

       -e quiet=set
       --quiet=set
       --silent=set
       --silence=set
                   Suppress various information messages.  The default is
                   quiet=none.  set can include the following elements:

                   attach           Suppress messages about attaching and
                                    detaching ("[ Process NNNN attached ]", "[
                                    Process NNNN detached ]").
                   exit             Suppress messages about process exits ("+++
                                    exited with SSS +++").
                   path-resolution  Suppress messages about resolution of paths
                                    provided via the -P option ("Requested path
                                    "..." resolved into "..."").
                   personality      Suppress messages about process personality
                                    changes ("[ Process PID=NNNN runs in PPP
                                    mode. ]").
                   thread-execve
                   superseded       Suppress messages about process being
                                    superseded by execve(2) in another thread
                                    ("+++ superseded by execve in pid NNNN
                                    +++").

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

                   path    Print file paths.
                   socket  Print socket protocol-specific information,
                   dev     Print character/block device numbers.
                   pidfd   Print PIDs associated with pidfd file descriptors.

       -e kvm=vcpu
       --kvm=vcpu  Print the exit reason of kvm vcpu.  Requires Linux kernel
                   version 4.16.0 or higher.

       -i
       --instruction-pointer
                   Print the instruction pointer at the time of the system call.

       -n
       --syscall-number
                   Print the syscall number.

       -k
       --stack-traces
                   Print the execution stack trace of the traced processes after
                   each system call.

       -o filename
       --output=filename
                   Write 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.  The latter is not compatible with -ff option
                   currently.

       -A
       --output-append-mode
                   Open the file provided in the -o option in append mode.

       -q
       --quiet
       --quiet=attach,personality
                   Suppress 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
                   Suppress messages attaching, detaching, personality changes,
                   and about process exit status.

       -qqq
       --quiet=all Suppress all suppressible messages (please refer to the -e
                   quiet option description for the full list of suppressible
                   messages).

       -r
       --relative-timestamps[=precision]
                   Print 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
                   since -r option uses the monotonic clock time for measuring
                   time difference and not the wall clock time, its measurements
                   can differ from the difference in time reported by the -t
                   option.

       -s strsize
       --string-limit=strsize
                   Specify 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]]
                   Prefix 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:

                   none          No time stamp is printed.  Can be used to
                                 override the previous setting.
                   time          Wall clock time (strftime(3) format string is
                                 %T).
                   unix          Number of seconds since the epoch (strftime(3)
                                 format string is %s).

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

       -tt
       --absolute-timestamps=precision:us
                   If given twice, the time printed will include the
                   microseconds.

       -ttt
       --absolute-timestamps=format:unix,precision:us
                   If given thrice, the time printed will include the
                   microseconds and the leading portion will be printed as the
                   number of seconds since the epoch.

       -T
       --syscall-times[=precision]
                   Show 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 Print unabbreviated versions of environment, stat, termios,
                   etc.  calls.  These structures are very common in calls and
                   so the default behavior displays a reasonable subset of
                   structure members.  Use this option to get all of the gory
                   details.

       -x
       --strings-in-hex=non-ascii
                   Print all non-ASCII strings in hexadecimal string format.

       -xx
       --strings-in-hex
       --strings-in-hex=all
                   Print all strings in hexadecimal string format.

       -X format
       --const-print-style=format
                   Set the format for printing of named constants and flags.
                   Supported format values are:

                   raw       Raw number output, without decoding.
                   abbrev    Output a named constant or a set of flags instead
                             of the raw number if they are found.  This is the
                             default strace behaviour.
                   verbose   Output both the raw value and the decoded string
                             (as a comment).

       -y
       --decode-fds
       --decode-fds=path
                   Print paths associated with file descriptor arguments.

       -yy
       --decode-fds=all
                   Print 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
                   If strace and tracee are in different PID namespaces, print
                   PIDs in strace's namespace, too.

   Statistics
       -c
       --summary-only
                   Count time, calls, and errors for each system call and report
                   a summary on program exit, suppressing the regular output.
                   This attempts to show system time (CPU time spent running in
                   the kernel) 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 print regular output while processes are
                   running.

       -O overhead
       --summary-syscall-overhead =overhead
                   Set the overhead for tracing system calls to overhead.  This
                   is useful for overriding the default heuristic for guessing
                   how much time is spent in mere measuring when timing system
                   calls using 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
                   Sort the output of the histogram printed by the -c option by
                   the specified criterion.  Legal 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
                   Configure a set (and order) of columns being shown in the
                   call summary.  The columns argument is a comma-separated list
                   with items being one of the following:

                   time-percent (or time)              Percentage of cumulative
                                                       time consumed by a
                                                       specific system call.
                   total-time (or time-total)          Total system (or wall
                                                       clock, if -w option is
                                                       provided) time consumed
                                                       by a specific system
                                                       call.
                   min-time (or shortest or time-min)  Minimum observed call
                                                       duration.
                   max-time (or longest or time-max)   Maximum observed call
                                                       duration.
                   avg-time (or time-avg)              Average call duration.
                   calls (or count)                    Call count.
                   errors (or error)                   Error count.
                   name (or syscall or syscall-name)   Syscall name.

                   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
                   Summarise the time difference between the beginning and end
                   of each system call.  The default is to summarise the system
                   time.

   Tampering
       -e 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]
       --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]
                   Perform syscall tampering for the specified set of syscalls.
                   The syntax of the syscall_set specification is the same as in
                   the -e trace option.

                   At least one of error, retval, signal, delay_enter, or
                   delay_exit options has to be specified.  error and retval are
                   mutually exclusive.

                   If :error=errno option is specified, a fault is injected into
                   a syscall invocation: the syscall number is replaced by -1
                   which corresponds to an invalid syscall (unless a syscall is
                   specified with :syscall= option), and the error code is
                   specified using a symbolic errno value like ENOSYS or a
                   numeric value within 1..4095 range.

                   If :retval=value option is specified, success injection is
                   performed: the syscall number is replaced by -1, but a bogus
                   success value is returned to the callee.

                   If :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 syscall
                   specified by the set.

                   If :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 syscall, respectively.  The format of delay
                   specification is described in section Time specification
                   format description.

                   If :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).
                   :poke_enter modifies memory on syscall enter, and :poke_exit
                   - on exit.

                   If :signal=sig option is specified without :error=errno,
                   :retval=value or :delay_{enter,exit}=usecs options, then only
                   a signal sig is delivered without a syscall fault or delay
                   injection.  Conversely, :error=errno or :retval=value option
                   without :delay_enter=delay, :delay_exit=delay or :signal=sig
                   options injects a fault without delivering a signal or
                   injecting a delay, etc.

                   If both :error=errno or :retval=value and :signal=sig options
                   are specified, then both a fault or success is injected and a
                   signal is delivered.

                   if :syscall=syscall option is specified, the corresponding
                   syscall with no side effects is injected instead of -1.
                   Currently, only "pure" (see -e trace=%pure description)
                   syscalls can be specified there.

                   Unless a :when=expr subexpression is specified, an injection
                   is being made into every invocation of each syscall from the
                   set.

                   The format of the subexpression is:

                             first[..last][+[step]]

                   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:

                   first             For every syscall from the set, perform an
                                     injection for the syscall invocation number
                                     first only.
                   first..last       For every syscall from the set, perform an
                                     injection for the syscall invocation number
                                     first and all subsequent invocations until
                                     the invocation number last (inclusive).
                   first+            For every syscall from the set, perform
                                     injections for the syscall invocation
                                     number first and all subsequent
                                     invocations.
                   first..last+      For every syscall from the set, perform
                                     injections for the syscall invocation
                                     number first and all subsequent invocations
                                     until the invocation number last
                                     (inclusive).
                   first+step        For every syscall from the set, perform
                                     injections for syscall invocations number
                                     first, first+step, first+step+step, and so
                                     on.
                   first..last+step  Same as the previous, but consider only
                                     syscall invocations with numbers up to last
                                     (inclusive).

                   For example, to fail each third and subsequent chdir syscalls
                   with ENOENT, use -e 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 only one error= or
                   retval= specification, and only one signal= specification.
                   If an injection expression contains multiple when=
                   specifications, the last one takes precedence.

                   Accounting of syscalls that are subject to injection is done
                   per syscall and per tracee.

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

       -e fault=syscall_set[:error=errno][:when=expr]
       --fault=syscall_set[:error=errno][:when=expr]
                   Perform syscall fault injection for the specified set of
                   syscalls.

                   This is equivalent to more generic -e inject= expression with
                   default value of errno option set to ENOSYS.

   Miscellaneous
       -d
       --debug     Show 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.
                   Usage of multiple instances of -F option is still equivalent
                   to a single -f, and it is ignored at all if used along with
                   one or more instances of -f option.

       -h
       --help      Print the help summary.

       --seccomp-bpf
                   Try to enable use of seccomp-bpf (see seccomp(2)) to have
                   ptrace(2)-stops only when system calls that are being traced
                   occur in the traced processes.  This option has no effect
                   unless -f/--follow-forks is also specified.  --seccomp-bpf 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.  In cases when
                   seccomp-bpf filter setup failed, strace proceeds as usual and
                   stops traced processes on every system call.

       -V
       --version   Print the version number of strace.

   Time specification format description
       Time values can be specified as a decimal floating point number (in a
       format accepted by strtod(3)), optionally followed by one of the
       following suffices that specify the unit of time: s (seconds), ms
       (milliseconds), us (microseconds), or ns (nanoseconds).  If no suffix is
       specified, the value is interpreted as microseconds.

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

DIAGNOSTICS
       When command exits, strace exits with the same exit status.  If command
       is terminated by a signal, strace terminates itself with the same signal,
       so that strace can be used as a wrapper process transparent to the
       invoking parent process.  Note that parent-child relationship (signal
       stop notifications, getppid(2) value, etc) between traced process and its
       parent are not preserved unless -D is used.

       When using -p without a command, the exit status of strace is zero unless
       no processes has been attached or there was an unexpected error in doing
       the tracing.

SETUID INSTALLATION
       If strace is installed setuid to root then the invoking user will be able
       to attach to and trace processes owned by any user.  In addition setuid
       and setgid programs will be executed and traced with the correct
       effective privileges.  Since only users trusted with full root privileges
       should be allowed to do these things, it only makes sense to install
       strace as setuid to root when the users who can execute it are restricted
       to those users who have this trust.  For example, it makes sense to
       install a special version of strace with mode 'rwsr-xr--', user root and
       group trace, where members of the trace group are trusted users.  If you
       do use this feature, please remember to install a regular non-setuid
       version of strace for ordinary users to use.

MULTIPLE PERSONALITIES SUPPORT
       On some architectures, strace supports decoding of syscalls for processes
       that use different ABI rather than the one strace uses.  Specifically, in
       addition to decoding native ABI, strace can decode the following ABIs on
       the following architectures:

       ┌───────────────────┬─────────────────────────┐
       │Architecture       ABIs supported          │
       ├───────────────────┼─────────────────────────┤
       │x86_64             │ i386, x32 [1]; i386 [2] │
       ├───────────────────┼─────────────────────────┤
       │AArch64            │ ARM 32-bit EABI         │
       ├───────────────────┼─────────────────────────┤
       │PowerPC 64-bit [3] │ PowerPC 32-bit          │
       ├───────────────────┼─────────────────────────┤
       │s390x              │ s390                    │
       ├───────────────────┼─────────────────────────┤
       │SPARC 64-bit       │ SPARC 32-bit            │
       ├───────────────────┼─────────────────────────┤
       │TILE 64-bit        │ TILE 32-bit             │
       └───────────────────┴─────────────────────────┘
       [1]  When strace is built as an x86_64 application
       [2]  When strace is built as an x32 application
       [3]  Big endian only

       This support is optional and relies on ability to generate and parse
       structure definitions during the build time.  Please refer to the output
       of the strace -V command in order to figure out what support is available
       in your strace build ("non-native" refers to an ABI that differs from the
       ABI strace has):

       m32-mpers      strace can trace and properly decode non-native 32-bit
                      binaries.
       no-m32-mpers   strace can trace, but cannot properly decode non-native
                      32-bit binaries.
       mx32-mpers     strace can trace and properly decode non-native
                      32-on-64-bit binaries.
       no-mx32-mpers  strace can trace, but cannot properly decode non-native
                      32-on-64-bit binaries.

       If the output contains neither m32-mpers nor no-m32-mpers, then decoding
       of non-native 32-bit binaries is not implemented at all or not
       applicable.

       Likewise, if the output contains neither mx32-mpers nor no-mx32-mpers,
       then decoding of non-native 32-on-64-bit binaries is not implemented at
       all or not applicable.

NOTES
       It is a pity that so much tracing clutter is produced by systems
       employing shared libraries.

       It is instructive to think about system call inputs and outputs as data-
       flow across the user/kernel boundary.  Because user-space and kernel-
       space are separate and address-protected, it is sometimes possible to
       make deductive inferences about process behavior using inputs and outputs
       as propositions.

       In some cases, a system call will differ from the documented behavior or
       have a different name.  For example, the faccessat(2) system call does
       not have flags argument, and the setrlimit(2) library function uses
       prlimit64(2) system call on modern (2.6.38+) kernels.  These
       discrepancies are normal but idiosyncratic characteristics of the system
       call interface and are accounted for by C library wrapper functions.

       Some system calls have different names in different architectures and
       personalities.  In these cases, system call filtering and printing uses
       the names that match corresponding __NR_* kernel macros of the tracee's
       architecture and personality.  There are two exceptions from this general
       rule: arm_fadvise64_64(2) ARM syscall and xtensa_fadvise64_64(2) Xtensa
       syscall are filtered and printed as fadvise64_64(2).

       On x32, syscalls that are intended to be used by 64-bit processes and not
       x32 ones (for example, readv(2), that has syscall number 19 on x86_64,
       with its x32 counterpart has syscall number 515), but called with
       __X32_SYSCALL_BIT flag being set, are designated with #64 suffix.

       On some platforms a process that is attached to with the -p option may
       observe a spurious EINTR return from the current system call that is not
       restartable.  (Ideally, all system calls should be restarted on strace
       attach, making the attach invisible to the traced process, but a few
       system calls aren't.  Arguably, every instance of such behavior is a
       kernel bug.)  This may have an unpredictable effect on the process if the
       process takes no action to restart the system call.

       As strace executes the specified command directly and does not employ a
       shell for that, scripts without shebang that usually run just fine when
       invoked by shell fail to execute with ENOEXEC error.  It is advisable to
       manually supply a shell as a command with the script as its argument.

BUGS
       Programs that use the setuid bit do not have effective user ID privileges
       while being traced.

       A traced process runs slowly (but check out the --seccomp-bpf option).

       Traced processes which are descended from command may be left running
       after an interrupt signal (CTRL-C).

HISTORY
       The original strace was written by Paul Kranenburg for SunOS and was
       inspired by its trace utility.  The SunOS version of strace was ported to
       Linux and enhanced by Branko Lankester, who also wrote the Linux kernel
       support.  Even though Paul released strace 2.5 in 1992, Branko's work was
       based on Paul's strace 1.5 release from 1991.  In 1993, Rick Sladkey
       merged strace 2.5 for SunOS and the second release of strace for Linux,
       added many of the features of truss(1) from SVR4, and produced an strace
       that worked on both platforms.  In 1994 Rick ported strace to SVR4 and
       Solaris and wrote the automatic configuration support.  In 1995 he ported
       strace to Irix and tired of writing about himself in the third person.

       Beginning with 1996, strace was maintained by Wichert Akkerman.  During
       his tenure, strace development migrated to CVS; ports to FreeBSD and many
       architectures on Linux (including ARM, IA-64, MIPS, PA-RISC, PowerPC,
       s390, SPARC) were introduced.  In 2002, the burden of strace
       maintainership was transferred to Roland McGrath.  Since then, strace
       gained support for several new Linux architectures (AMD64, s390x,
       SuperH), bi-architecture support for some of them, and received numerous
       additions and improvements in syscalls decoders on Linux; strace
       development migrated to git during that period.  Since 2009, strace is
       actively maintained by Dmitry Levin.  strace gained support for AArch64,
       ARC, AVR32, Blackfin, Meta, Nios II, OpenRISC 1000, RISC-V, Tile/TileGx,
       Xtensa architectures since that time.  In 2012, unmaintained and
       apparently broken support for non-Linux operating systems was removed.
       Also, in 2012 strace gained support for path tracing and file descriptor
       path decoding.  In 2014, support for stack traces printing was added.  In
       2016, syscall fault injection was implemented.

       For the additional information, please refer to the NEWS file and strace
       repository commit log.

REPORTING BUGS
       Problems with strace should be reported to the strace mailing list
       ⟨mailto:strace-devel@lists.strace.io⟩.

SEE ALSO
       strace-log-merge(1), ltrace(1), perf-trace(1), trace-cmd(1), time(1),
       ptrace(2), proc(5)

       strace Home Page ⟨https://strace.io/AUTHORS
       The complete list of strace contributors can be found in the CREDITS
       file.



strace 5.13                        2021-04-04                          STRACE(1)