strace

STRACE(1)                   General Commands Manual                  STRACE(1)

NAME
       strace - trace system calls and signals

SYNOPSIS
       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] }

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.  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 in-
       terface, 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 ar-
       ranges 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 us-
       age 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 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
       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)  li-
       brary 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.

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, abbrev, verbose, raw, sig-
                   nal, read, write, fault, inject, status, 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  sys-
                   tem 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 vari-
                   ables.

       -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 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
       --user=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-
                   leges.

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

       -DDD        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          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.

       -ff         If  the  -o  filename  option  is in effect, each processes
                   trace is written to filename.pid where pid is  the  numeric
                   process  id of each process.  This is incompatible with -c,
                   since no per-process counts are kept.

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

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

                   1   no signals are blocked;
                   2   fatal signals are blocked while decoding  syscall  (de-
                       fault);
                   3   fatal  signals  are  always blocked (default if -o FILE
                       PROG);
                   4   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 Ex-
                                pression 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 per-
                                sonality.

                   %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,un-
                                link,...  which is useful to seeing what files
                                the process is referencing.  Furthermore,  us-
                                ing  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 preced-
                                ing  percent  sign ("-e trace=file") is depre-
                                cated.

                   %process
                   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.

                   %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  syn-
                                tax  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 and fstatat 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  ef-
                                fect       can      be      achieved      with
                                -e trace=/^(.*_)?statv?fs regular expression.

                   %fstatfs     Trace fstatfs,  fstatfs64,  fstatvfs,  osf_fs-
                                tatfs,  and  osf_fstatfs64  system calls.  The
                                same effect can be achieved with -e trace=/fs-
                                tatv?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   ex-
                                pression.

                   %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
       --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 quali-
                   fier, because strace waits for system calls to  return  be-
                   fore  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  sta-
                                tus=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 op-
                   tions can be used to specify several paths.

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

       -Z          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 ab-
                   brev=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  ver-
                   bose=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  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 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.

       -k
       --stack-traces
                   Print the execution stack trace of the traced processes af-
                   ter 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 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.

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

       -q          Suppress  messages  about  attaching,  detaching etc.  This
                   happens automatically when output is redirected to  a  file
                   and the command is run directly instead of attaching.

       -qq         If  given  twice, suppress messages about process exit sta-
                   tus.

       -r          Print a relative timestamp upon entry to each system  call.
                   This  records  the time difference between the beginning of
                   successive system calls.  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.

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

       -tt         If given twice, the time printed will include the microsec-
                   onds.

       -ttt        If given thrice, the time  printed  will  include  the  mi-
                   croseconds  and  the leading portion will be printed as the
                   number of seconds since the epoch.

       -T          Show the time spent in system calls.  This records the time
                   difference between the beginning and the end of each system
                   call.

       -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          Print all non-ASCII strings in hexadecimal string format.

       -xx         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          Print paths associated with file descriptor arguments.

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

   Statistics
       -c
       --summary-only
                   Count time, calls, and errors for each system call and  re-
                   port  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 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
       --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_total or total_time), calls (or count), errors (or er-
                   ror), name (or syscall or syscall_name),  and  nothing  (or
                   none); default is time.

       -w
       --summary-wall-clock
                   Summarise the time difference between the beginning and end
                   of each system call.  The default is to summarise the  sys-
                   tem time.

   Tampering
       -e inject=syscall_set[:error=errno|:retval=value][:sig-
       nal=sig][:syscall=syscall][:delay_en-
       ter=delay][:delay_exit=delay][:when=expr]
       --inject=syscall_set[:error=errno|:retval=value][:sig-
       nal=sig][:syscall=syscall][:delay_en-
       ter=delay][:delay_exit=delay][: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 de-
                   lay_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 bo-
                   gus 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  de-
                   layed  by time period specified by delay on entering or ex-
                   iting the syscall, respectively.  The format of delay spec-
                   ification 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  op-
                   tions  are  specified,  then both a fault or success is in-
                   jected 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 in-
                               jection 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:er-
                   ror=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]
       --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  equiva-
                   lent 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
                   Enable (experimental) usage of seccomp-bpf (see seccomp(2))
                   to have ptrace(2)-stops only when system calls that are be-
                   ing 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.

       -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  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 in-
       ject=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 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 un-
       less 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  privi-
       leges  should be allowed to do these things, it only makes sense to in-
       stall 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.

MULTIPLE PERSONALITIES SUPPORT
       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
                      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  decod-
       ing  of non-native 32-bit binaries is not implemented at all or not ap-
       plicable.

       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  em-
       ploying 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-
       ment.

BUGS
       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).

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  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, Su-
       perH), bi-architecture support for some of them, and received  numerous
       additions and improvements in syscalls decoders on Linux; strace devel-
       opment migrated to git during that period.  Since 2009, strace  is  ac-
       tively  maintained by Dmitry Levin.  strace gained support for AArch64,
       ARC, AVR32, Blackfin, Meta, Nios II, OpenSISC  1000,  RISC-V,  Tile/Ti-
       leGx,  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 descrip-
       tor path decoding.  In 2014, support  for  stack  traces  printing  was
       added.  In 2016, syscall fault injection was implemented.

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

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

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

       strace Home Page <https://strace.io/>

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

strace 5.5                        2020-02-04                         STRACE(1)
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