Q: long option aliases

Eugene Syromiatnikov esyr at redhat.com
Wed Mar 4 17:27:01 UTC 2020

On Mon, Mar 02, 2020 at 09:15:35PM +0100, Eugene Syromiatnikov wrote:
> Hello.
> The strace's master branch now includes commits that add long option
> aliases for all of the existing options.  I'd like to ask for feedback:
> do these aliases look natural/sensible, does the introduced syntax for some
> options (like --quiet, --daemonize, --decode-fds, --absolute-timestamps)
> make sense?

For the reference, here's the current rendering of strace.1:
STRACE(1)                   General Commands Manual                  STRACE(1)

       strace - trace system calls and signals

       strace [-ACdffhikqqrtttTvVwxxyyzZ] [-I n] [-b execve] [-e expr]...
              [-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] [-P path]... [-p pid]... [--seccomp-bpf] { -p pid |
              [-DDD] [-E var[=val]]... [-u username] command [args] }

       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.  Sys‐
       tem  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  strac‐
       ing 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 unfin‐
       ished.  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  third  argument  of open(2) is 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

       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 mem‐
       ber 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

           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  ele‐
       ments.  Here is an example from the command id(1) on a system with sup‐
       plementary 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, prepar‐
       ing 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.

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


                   where qualifier is one of trace (or t), abbrev (or a), ver‐
                   bose (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 sym‐
                   bol 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.

       -E var=val
                   Run command with var=val in its list of  environment  vari‐

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

       -p pid
                   Attach to the process with the process  ID  pid  and  begin
                   tracing.  The trace may be terminated at any time by a key‐
                   board 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
                   Run  command  with the user ID, group ID, and supplementary
                   groups of username.  This option is only useful  when  run‐
                   ning  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 privi‐

       -b 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.

                   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.

                   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.

                   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.

                   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.

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

       --follow-forks --output-separately
                   Combine the effects of  --follow-forks  and  --output-sepa‐
                   rately  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
                   When strace can be interrupted by signals (such as pressing

                   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

       -e 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

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

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

                   syscall at x32  Trace syscall only for the  32-on-64-bit  per‐

                   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 abbrevia‐
                                tion  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      Trace  all  system calls which involve process
                                management.  This is useful for  watching  the
                                fork,  wait, and exec steps of a process.  The
                                syntax without a preceding percent  sign  ("-e
                                trace=process") is deprecated.

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

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

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

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

                   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 and fstatat syscall variants.

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

                   %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  statis‐
                                tics  (statfs-like,  fstatfs-like, and ustat).
                                The  same  effect   can   be   achieved   with
                                -e trace=/statv?fs|fsstat|ustat        regular

                   %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), get‐
                                gid(2),  getgid32(2),  getpagesize(2),   getp‐
                                grp(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
                   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
                   Print  only  system calls with the specified return status.
                   The default is status=all.  When using  the  status  quali‐
                   fier,  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
                   failed       Trace system calls that returned with an error
                                code.   The  -Z  option has the effect of sta‐
                   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  only  system  calls  accessing  path.   Multiple  -P
                   options can be used to specify several paths.

                   Print only syscalls that returned without an error code.

                   Print only syscalls that returned with an error code.

   Output format
       -a column
                   Align  return  values  in a specific column (default column

       -e 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
                   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 ver‐

       -e 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 hexadeci‐
                   mal.  This is mostly useful if you don't trust the decoding
                   or  you  need  to know the actual numeric value of an argu‐
                   ment.  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
                   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 personal‐
                                    ity changes ("[ Process PID=NNNN  runs  in
                                    PPP mode. ]").
                   superseded       Suppress   messages  about  process  being
                                    superseded by execve(2) in another  thread
                                    ("+++  superseded  by  execve  in pid NNNN

       -e decode-fds=set
                   Decode various information associated  with  file  descrip‐
                   tors.  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.

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

                   Print  the  instruction  pointer  at the time of the system

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

       -o filename
                   Write  the trace output to the file filename rather than to
                   stderr.  filename.pid form is used if -ff  option  is  sup‐
                   plied.  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.

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

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

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

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

                   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 mea‐
                   suring  time  difference  and  not the wall clock time, its
                   measurements  can  differ  from  the  difference  in   time
                   reported by the -t option.

       -s 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.

                   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
                   unix          Number  of  seconds  since  the  epoch (strf‐
                                 time(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.

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

                   If given twice, the time printed will include the microsec‐

                   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.

                   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 (mil‐
                   liseconds), us (microseconds),  or  ns  (nanoseconds),  and
                   allows  setting  the precision of time value being printed.
                   Default is us (microseconds).

       --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

                   Print all non-ASCII strings in hexadecimal string format.

                   Print all strings in hexadecimal string format.

       -X 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).

                   Print paths associated with file descriptor arguments.

                   Print protocol specific information associated with  socket
                   file descriptors, and block/character device number associ‐
                   ated with device file descriptors.

                   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.

       --summary   Like  -c  but also print regular output while processes are

       -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 tim‐
                   ing  system calls using the -c option.  The accuracy of the
                   heuristic can be gauged by timing a given program run with‐
                   out  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  sec‐
                   tion Time specification format description.

       -S sortby
                   Sort  the  output of the histogram printed by the -c option
                   by the specified criterion.   Legal  values  are  time  (or
                   time_total  or  total_time),  calls  (or count), errors (or
                   error), name (or syscall or syscall_name), and nothing  (or
                   none); default is time.

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

       -e inject=syscall_set[:error=errno|:retval=value][:sig‐
                   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 :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 injec‐
                   tion is being made into every invocation  of  each  syscall
                   from the set.

                   The format of the subexpression is one of the following:

                   first       For  every  syscall  from  the  set, perform an
                               injection for  the  syscall  invocation  number
                               first only.
                   first+      For  every syscall from the set, perform injec‐
                               tions for the syscall invocation  number  first
                               and all subsequent invocations.
                   first+step  For  every syscall from the set, perform injec‐
                               tions for  syscall  invocations  number  first,
                               first+step, first+step+step, and so on.

                   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.

                   An injection expression can contain only one error= or ret‐
                   val= specification, and only one signal= specification.  If
                   an  injection expression contains multiple when= specifica‐
                   tions, 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/uran‐
                   dom -e inject=file:error=ENOENT.

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

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

       --debug     Show some debugging output of strace itself on the standard

       -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  equiva‐
                   lent to a single -f, and it is ignored at all if used along
                   with one or more instances of -f option.

       --help      Print the help summary.

                   Enable (experimental) usage of seccomp-bpf (see seccomp(2))
                   to  have  ptrace(2)-stops  only  when system calls that are
                   being traced occur in the traced processes.  Implies the -f
                   option.  An attempt to rely on seccomp-bpf to filter system
                   calls 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.   --seccomp-bpf  is  also
                   ineffective  on processes attached using -p.  In cases when
                   seccomp-bpf filter setup failed, strace proceeds  as  usual
                   and stops traced processes on every system call.

       --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  fol‐
       lowing  suffices  that  specify the unit of time: s (seconds), ms (mil‐
       liseconds), 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.

       When command exits, strace exits with the same exit status.  If command
       is  terminated by a signal, strace terminates itself with the same sig‐
       nal, 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.

       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  privi‐
       leges  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  regu‐
       lar non-setuid version of strace for ordinary users to use.

       On  some  architectures,  strace supports decoding of syscalls for pro‐
       cesses that use different ABI rather than the one strace uses.  Specif‐
       ically,  in addition to decoding native ABI, strace can decode the fol‐
       lowing 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 out‐
       put 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 dif‐
       fers from the ABI strace has):

       m32-mpers      strace can trace and properly decode  non-native  32-bit
       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  decod‐
       ing  of  non-native  32-bit  binaries  is not implemented at all or not

       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.

       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 ker‐
       nel-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  dis‐
       crepancies  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 gen‐
       eral 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 argu‐

       Programs that use the setuid bit do not have effective user  ID  privi‐
       leges while being traced.

       A traced process runs slowly.

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

       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  pro‐
       duced  an  strace  that  worked on both platforms.  In 1994 Rick ported
       strace to SVR4 and Solaris and wrote the automatic  configuration  sup‐
       port.  In 1995 he ported strace to Irix and tired of writing about him‐
       self 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,  Pow‐
       erPC,  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  numer‐
       ous  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,  OpenSISC  1000,  RISC-V,
       Tile/TileGx,  Xtensa  architectures  since that time.  In 2012, unmain‐
       tained 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.

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

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

       strace Home Page ⟨https://strace.io/⟩

       The complete list of strace contributors can be found  in  the  CREDITS

strace       2020-02-24                         STRACE(1)

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