Provided by: strace_4.25-0ubuntu1_amd64 bug

NAME

       strace - trace system calls and signals

SYNOPSIS

       strace [-ACdffhikqrtttTvVxxy] [-I n] [-b execve] [-e expr]... [-a column] [-o file]
              [-s strsize] [-X format] [-P path]... [-p pid]... { -p pid | [-D] [-E var[=val]]...
              [-u username] command [args] }

       strace -c [-df] [-I n] [-b execve] [-e expr]... [-O overhead] [-S sortby] [-P path]...
              [-p pid]... { -p pid | [-D] [-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 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(1, 3), ...}) = 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  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  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" 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

   Output format
       -a column   Align return values in a specific column (default column 40).

       -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.

       -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 microseconds.   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.

       -S sortby   Sort  the  output  of  the histogram printed by the -c option by the specified
                   criterion.  Legal values are time, calls, name, and nothing (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.

   Filtering
       -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,  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.

       -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 (deprecated)
                   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 in the list.  Betchya woulda forgot that one.

       -e trace=%process
       -e trace=process (deprecated)
                   Trace  all  system calls which involve process management.  This is useful for
                   watching the fork, wait, and exec steps of a process.

       -e trace=%network
       -e trace=network (deprecated)
                   Trace all the network related system calls.

       -e trace=%signal
       -e trace=signal (deprecated)
                   Trace all signal related system calls.

       -e trace=%ipc
       -e trace=ipc (deprecated)
                   Trace all IPC related system calls.

       -e trace=%desc
       -e trace=desc (deprecated)
                   Trace all file descriptor related system calls.

       -e trace=%memory
       -e trace=memory (deprecated)
                   Trace all memory mapping related system calls.

       -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 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 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 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 inject=set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_enter=usecs][:delay_exit=usecs][: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=usecs  or  :delay_exit=usecs  options  are  specified,  delay
                   injection  is  performed: the tracee is delayed by at least usecs microseconds
                   on entering or exiting the syscall.

                   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=usecs,  :delay_exit=usecs 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.

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

       -P path     Trace only system calls accessing path.  Multiple -P options can  be  used  to
                   specify several paths.

       -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.

   Tracing
       -b syscall  If specified syscall is reached, detach from traced process.  Currently,  only
                   execve  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  detached grandchild, not as parent of the tracee.
                   This reduces the visible effect of strace by keeping the tracee a direct child
                   of the calling process.

       -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 ^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 (^Z) are always blocked (useful to  make  strace  -o
                   FILE PROG not stop on ^Z).

   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.

   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          Print the help summary.

       -V          Print the version number of strace.

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() 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:

       ┌───────────────┬──────────────────────────────────────────────────────────────────────────────────────────┐
       │ArchitectureABIs supported                                                                           │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │x86_64         │ i386, x32 (when built as an x86_64 application); i386 (when built as an x32 application) │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │AArch64        │ ARM 32-bit EABI                                                                          │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │PowerPC 64-bit │ PowerPC 32-bit                                                                           │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │RISC-V 64-bit  │ RISC-V 32-bit                                                                            │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │s390x          │ s390                                                                                     │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │SPARC 64-bit   │ SPARC 32-bit                                                                             │
       ├───────────────┼──────────────────────────────────────────────────────────────────────────────────────────┤
       │TILE 64-bit    │ TILE 32-bit                                                                              │
       └───────────────┴──────────────────────────────────────────────────────────────────────────────────────────┘
       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, 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)