Provided by: strace_5.11-0ubuntu1_amd64 bug

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:

       ┌───────────────────┬─────────────────────────┐
       │ArchitectureABIs 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.