Provided by: strace_5.5-3ubuntu1_amd64 bug


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

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

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

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

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

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

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

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

           [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 source.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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


                   where qualifier is one of trace, abbrev, verbose, raw,  signal,  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 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

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

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

       -p pid
                   Attach  to  the  process with the process ID pid and begin tracing.  The trace
                   may be terminated at any time by a keyboard interrupt signal (CTRL-C).  strace
                   will respond by detaching itself from the traced process(es) leaving it (them)
                   to continue running.  Multiple -p options  can  be  used  to  attach  to  many
                   processes  in addition to command (which is optional if at least one -p option
                   is given).  -p "`pidof PROG`" syntax is supported.

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

       -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.

       -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 effect 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
          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 obtain 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 (default);
                   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).

       -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 following:

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

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

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

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

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

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

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

                   process      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  syntax  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

                   %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   effect   can   be  achieved  with
                                -e trace=/^(.*_)?statv?fs regular expression.

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

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

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

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

       -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 qualifier, because strace waits for  system
                   calls  to  return  before  deciding whether they should be printed or not, the
                   traditional order of events may not be preserved anymore.  If two system calls
                   are executed by concurrent threads, strace will first print both the entry and
                   exit of the first system call to exit, regardless of  their  respective  entry
                   time.   The  entry  and exit of the second system call to exit will be printed
                   afterwards.  Here is an example when select(2)  is  called,  but  a  different
                   thread calls clock_gettime(2) before select(2) finishes:

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

                   set can include the following elements:

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

       -P path
                   Trace  only  system  calls accessing path.  Multiple -P options 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
                   Align return values in a specific column (default column 40).

       -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 verbose=all.

       -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
                   hexadecimal.   This  is  mostly  useful if you don't trust the decoding or you
                   need to know the actual numeric value of an argument.  See also -X raw option.

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

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

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

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

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

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

                   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

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

       -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
                   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 microseconds.

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

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

       --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
                   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 associated 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

       --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 timing system calls using the -c option.  The accuracy  of  the
                   heuristic  can  be gauged by timing a given program run without tracing (using
                   time(1)) and comparing the accumulated system call time to the total  produced
                   using -c.

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

       -S sortby
                   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 system time.

       -e inject=syscall_set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_enter=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 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

                   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  injection  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 injections for the syscall
                               invocation number first and all subsequent invocations.
                   first+step  For  every  syscall  from  the set, perform injections 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 retval= specification,
                   and only one signal=  specification.   If  an  injection  expression  contains
                   multiple when= specifications, the last one takes precedence.

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

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

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

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

       -F          This option is deprecated.  It is retained for backward compatibility only and
                   may  be  removed in future releases.  Usage of multiple instances of -F option
                   is still equivalent to a single -f, and it is ignored at  all  if  used  along
                   with one or more instances of -f option.

       --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 following suffices that specify the unit of
       time: s (seconds), ms (milliseconds), us  (microseconds),  or  ns  (nanoseconds).   If  no
       suffix is specified, the value is interpreted as microseconds.

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


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

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


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


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

       │ArchitectureABIs supported          │
       │x86_64             │ i386, x32 [1]; i386 [2] │
       │AArch64            │ ARM 32-bit EABI         │
       │PowerPC 64-bit [3] │ PowerPC 32-bit          │
       │s390x              │ s390                    │
       │SPARC 64-bit       │ SPARC 32-bit            │
       │TILE 64-bit        │ TILE 32-bit             │
       [1]  When strace is built as an x86_64 application
       [2]  When strace is built as an x32 application
       [3]  Big endian only

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

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

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

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


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

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

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

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

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

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

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


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

       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  produced  an strace that worked on both
       platforms.  In 1994 Rick ported strace  to  SVR4  and  Solaris  and  wrote  the  automatic
       configuration  support.   In  1995  he  ported  strace  to Irix and tired of writing about
       himself in the third person.

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

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


       Problems    with    strace    should    be   reported   to   the   strace   mailing   list


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

       strace Home Page ⟨⟩


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