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

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

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

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

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

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

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

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

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

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

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

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

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

       Here, the 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.

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=][!][?]value1[,[?]value2]...

                   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.  Question mark before
                   the syscall qualification allows suppression of error in
                   case no syscalls matched the qualification provided.
                   Appending one of "@64", "@32", or "@x32" suffixes to the
                   syscall qualification allows specifying syscalls only for
                   the 64-bit, 32-bit, or 32-on-64-bit personality,
                   respectively.  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  Run command with var=val in its list of environment
                   variables.

       -E 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.

   Tracing
       -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 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
                   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).

   Filtering
       -e trace=set
                   Trace only the specified set of system calls.  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 trace=/regex
                   Trace only those system calls that match the regex.  You
                   can use POSIX Extended Regular Expression syntax (see
                   regex(7)).

       -e trace=%file
       -e trace=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.

       -e trace=%process
       -e trace=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.

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

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

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

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

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

       -e trace=%stat
                   Trace stat syscall variants.

       -e trace=%lstat
                   Trace lstat syscall variants.

       -e trace=%fstat
                   Trace fstat and fstatat syscall variants.

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

       -e trace=%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.

       -e trace=%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.

       -e trace=%%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.

       -e trace=%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.

       -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=set
                   Abbreviate the output from printing each member of large
                   structures.  The default is abbrev=all.  The -v option has
                   the effect of abbrev=none.

       -e verbose=set
                   Dereference structures for the specified set of system
                   calls.  The default is verbose=all.

       -e raw=set  Print raw, undecoded arguments for the specified set of
                   system calls.  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 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
                   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 Print the exit reason of kvm vcpu.  Requires Linux kernel
                   version 4.16.0 or higher.

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

       -k          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
                   supplied.  If the argument begins with '|' or '!', the rest
                   of the argument is treated as a command and all output is
                   piped to it.  This is convenient for piping the debugging
                   output to a program without affecting the redirections of
                   executed programs.  The latter is not compatible with -ff
                   option currently.

       -A          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
                   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.

       -v          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.

   Statistics
       -c          Count time, calls, and errors for each system call and
                   report a summary on program exit, suppressing the regular
                   output.  This attempts to show system time (CPU time spent
                   running in the kernel) independent of wall clock time.  If
                   -c is used with -f, only aggregate totals for all traced
                   processes are kept.

       -C          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.

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

   Tampering
       -e inject=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.

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

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

       -h,
       --help      Print the help summary.

       --seccomp-bpf
                   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.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

       A traced process runs slowly.

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

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

       Beginning with 1996, strace was maintained by Wichert Akkerman.  During
       his tenure, strace development migrated to CVS; ports to FreeBSD and
       many architectures on Linux (including ARM, IA-64, MIPS, PA-RISC,
       PowerPC, s390, SPARC) were introduced.  In 2002, the burden of strace
       maintainership was transferred to Roland McGrath.  Since then, strace
       gained support for several new Linux architectures (AMD64, s390x,
       SuperH), bi-architecture support for some of them, and received
       numerous additions and improvements in syscalls decoders on Linux;
       strace development migrated to git during that period.  Since 2009,
       strace is actively maintained by Dmitry Levin.  strace gained support
       for AArch64, ARC, AVR32, Blackfin, Meta, Nios II, 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 log.

REPORTING BUGS
       Problems with strace should be reported to the strace mailing list at
       <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 5.4                        2019-10-07                         STRACE(1)