# strace

## NAME



           strace - trace system calls and signals
    


## SYNOPSIS



           **strace**[**-ACdffhikkqqrtttTvVwxxyyYzZ**] [**-a** _column_] [**-b** _execve_]
                  [**-e** _expr_]... [**-I** _n_] [**-o** _file_] [**-O** _overhead_] [**-p** _pid_]...
                  [**-P** _path_]... [**-s** _strsize_] [**-S** _sortby_] [**-U** _columns_]
                  [**-X** _format_] [**--seccomp-bpf**]
                  [**--stack-trace-frame-limit** =_limit_] [**--syscall-limit=**_limit_]
                  [**--secontext**[=_format_]] [**--tips**[=_format_]] { **-p** _pid_ | [**-DDD**]
                  [**-E** _var_[=_val_]]... [**-u** _username_] _command_ [_args_] }
    
           **strace -c**[**-dfwzZ**] [**-b** _execve_] [**-e** _expr_]... [**-I** _n_] [**-O** _overhead_]
                  [**-p** _pid_]... [**-P** _path_]... [**-S** _sortby_] [**-U** _columns_]
                  [**--seccomp-bpf**] [**--syscall-limit=**_limit_] [**--tips**[=_format_]] {
                  **-p** _pid_ | [**-DDD**] [**-E** _var_[=_val_]]... [**-u** _username_] _command_
                  [_args_] }
    
           **strace --tips**[=_format_]
    


## DESCRIPTION



           In its simplest use case, **strace** runs the specified _command_ until
           it exits.  It intercepts and records the system calls made by a
           process and the signals a process receives.  The name of each
           system call, its arguments, and its return value are printed to
           standard error or to the file specified with the **-o** option.
    
           **strace** is a useful diagnostic, instructional, and debugging tool.
           System administrators, diagnosticians, and troubleshooters will
           find it invaluable for solving problems with programs for which
           source code is not readily available, as recompilation is not
           required for tracing.  Students, hackers, and the overly-curious
           will discover that a great deal can be learned about a system and
           its system calls by tracing even ordinary programs.  Programmers
           will find that since system calls and signals occur 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 tracing the command "cat /dev/null" is:
    
               open("/dev/null", O_RDONLY) = 3
    
           Errors, typically indicated by 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 a signal symbol and a decoded _siginfo_
           structure.  An excerpt from tracing 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 while another is called from a
           different thread or process, **strace** will attempt to preserve the
           order of these events and mark the ongoing call as _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, {tv_sec=1130322148, tv_nsec=3977000}) = 0
               [pid 28772] <... select resumed> )      = 1 (in [3])
    
           The interruption of a (restartable) system call by a signal
           delivery is handled differently, as the kernel terminates the
           system call and arranges for its immediate re-execution after the
           signal handler completes.
    
               read(0, 0x7ffff72cf5cf, 1)              = ? ERESTARTSYS (To be restarted)
               --- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
               rt_sigreturn({mask=[]})                 = 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 second and third arguments of open(2) are decoded by
           breaking down the flag argument into its three bitwise-OR
           constituents and printing the mode value in octal, following
           tradition.  Where traditional or native usage differs from ANSI or
           POSIX, the latter forms are preferred.  In some cases, **strace**
           output has proven to be more readable than the source code itself.
    
           Structure pointers are dereferenced, and their 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, note that in this example, 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.  The
           pointer's value is displayed because the structure it points to
           was not populated due to the error.
    
           System calls unknown to **strace** are printed in a raw format, with
           the hexadecimal system call number 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
           standard 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, pointers to
           basic types and arrays are printed using square brackets with
           commas separating the 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 it is more
           valuable to print the unset elements.  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_
                  Modifies which events to trace or how to trace them by
                  specifying a qualifying expression.  The format of the
                  expression is:
    
                                 [_qualifier_**=**][**!**]_value_[**,**_value_]...
    
                  where _qualifier_ is one of **trace**(or **t**), **trace-fds**(or
                  **trace-fd** or **fd** or **fds**), **abbrev**(or **a**), **verbose**(or **v**), **raw**
                  (or **x**), **signal**(or **signals** or **s**), **read**(or **reads** or **r**),
                  **write**(or **writes** or **w**), **fault** , **inject** , **status** , **quiet**(or
                  **silent** or **silence** or **q**), **secontext** , **decode-fds**(or
                  **decode-fd**), **decode-pids**(or **decode-pid**), 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** is equivalent to
                  **-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** may be used to trace every event or no
                  events, respectively.
    
                  Note that some shells use the exclamation mark for history
                  expansion even inside quoted arguments.  In that case, the
                  exclamation mark must be escaped with a backslash.
    
       **Startup**
           **-E** _var_ =_val_
           **--env** =_var_ =_val_
                  Runs the command with the environment variable _var_ =_val_ set
                  for execution.
    
           **-E** _var_
           **--env** =_var_
                  Removes _var_ from the inherited environment variables before
                  executing the command.
    
           **-p** _pid_
           **--attach** =_pid_
                  Attaches 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 processes, leaving them to
                  continue running.
    
                  Multiple **-p** options can be used to attach to several
                  processes in addition to the command, which is optional if
                  at least one **-p** option is given.
    
                  A single **-p** option can accept multiple process IDs
                  separated by a comma (“,”), space (“ ”), tab, or newline.
                  Consequently, syntaxes like **-p** "$(pidof PROG)" and **-p**
                  "$(pgrep PROG)" are supported.
    
           **-u** _username_
           **--user** =_username_
                  Runs command with the user ID, group ID, and supplementary
                  groups of _username_.  This option is only useful when
                  running as root, as it enables the correct execution of
                  setuid and/or setgid binaries.  Unless this option is used,
                  setuid and setgid programs are executed without their
                  effective privileges.
           **-u** _UID:GID_
           **--user** =_UID:GID_
                  Alternative syntax where the program is started with
                  exactly the given user and group IDs, and an empty list of
                  supplementary groups.  In this case, user and group name
                  lookups are not performed.
    
           **--argv0** =_name_
                  Sets the executed command's argv[0] to _name_.  This is
                  useful for tracing multi-call executables that interpret
                  argv[0], such as busybox or kmod.
    
       **Tracing**
           **-b** _syscall_
           **--detach-on** =_syscall_
                  Detaches from the traced process if the specified system
                  call is reached.  Currently, only **execve** keyword is
                  supported, which includes execve(2) and execveat(2) system
                  calls.  This option is useful for tracing a multi-threaded
                  process with **-f** without also tracing its (potentially very
                  complex) child processes.
    
           **-D**
           **--daemonize**
           **--daemonize** =**grandchild**
                  Runs the tracer process as a grandchild of the tracee, not
                  as its parent.  This reduces the visible effect of **strace**
                  by keeping the tracee a direct child of the calling
                  process.
    
           **-DD**
           **--daemonize** =**pgroup**
           **--daemonize** =**pgrp**
                  Runs tracer process as tracee's grandchild in a separate
                  process group.  In addition to reducing the visible effect
                  of **strace** , this also prevents **strace** from being terminated
                  by a kill(2) signal sent to the entire process group.
    
           **-DDD**
           **--daemonize** =**session**
                  Runs the tracer process as the tracee's grandchild in a
                  separate session (known as "true daemonisation").  In
                  addition to reduction of the visible effect of **strace** , this
                  also prevents **strace** from being terminated upon session
                  termination.
    
           **-f**
           **--follow-forks**
                  Traces 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 if process _PID_ is multi-
                  threaded, using **-f -p** _PID_ attaches to all of its threads,
                  not just the one with _thread_id_ = _PID_.
    
           **--output-separately**
                  If the **--output** =_filename_ option is in effect, the trace for
                  each process is written to a separate _filename_._pid_ file,
                  where _pid_ is the process ID.
    
           **-ff**
           **--follow-forks --output-separately**
                  Combines the effects of **--follow-forks** and
                  **--output-separately** options.  This is incompatible with **-c** ,
                  since no per-process counts are kept.
    
                  Use strace-log-merge(1) to get a combined view of the log
                  files.
    
           **-I** _interruptible_
           **--interruptible** =_interruptible_
                  Controls when **strace** can be interrupted by signals (such as
                  pressing **CTRL-C**).
    
                  **1** , **anywhere**
                         no signals are blocked;
                  **2** , **waiting**
                         fatal signals are blocked while decoding system call
                         (default);
                  **3** , **never**
                         fatal signals are always blocked (default if **-o** _FILE_
                         _PROG_);
                  **4** , **never_tstp**
                         fatal signals and **SIGTSTP**(**CTRL-Z**) are always
                         blocked (useful to make **strace -o** _FILE PROG_ not stop
                         on **CTRL-Z** , default if **-D**).
    
           **--syscall-limit** =_limit_
                  Detaches all tracees after _limit_ system calls have been
                  captured.  System calls filtered out via **--trace** ,
                  **--trace-path** or **--status** options are not considered when
                  keeping track of the number of system calls that are
                  captured.
    
           **--kill-on-exit**
                  Applies the **PTRACE_O_EXITKILL** ptrace option to all tracees,
                  which sends a SIGKILL signal to a tracee if the tracer
                  exits.  This prevents tracees from being left running after
                  the tracer exits, as they will not be detached on cleanup.
                  **--kill-on-exit** is not compatible with **-p** /**--attach** options.
    
       **Filtering**
           **-e trace** =_syscall_set_
           **-e t** =_syscall_set_
           **--trace** =_syscall_set_
                  Traces only the specified set of system calls.  _syscall_set_
                  is defined as [**!**]_value_[**,**_value_], and _value_ can be one of the
                  following:
    
                  _syscall_
                         Traces specific system call, specified by its name
                         (see syscalls(2) for a reference, but also see
                         **NOTES**).
    
                  **?**_value_ A question mark preceding the qualification
                         suppresses errors if no matching system calls are
                         found.
    
                  _value_**@64**
                         Limits the system call specification described by
                         _value_ to the 64-bit personality.
    
                  _value_**@32**
                         Limits the system call specification described by
                         _value_ to the 32-bit personality.
    
                  _value_**@x32**
                         Limits the system call specification described by
                         _value_ to the x32 personality.
    
                  **all** Traces all system calls.
    
                  **/**_regex_ Traces only those system calls that match the _regex_.
                         You can use **POSIX** Extended Regular Expression syntax
                         (see regex(7)).
    
                  **%file**
                  **file** Traces all system calls that take a file name as an
                         argument.  You can think of this as an abbreviation
                         for **--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 newfstatat(2) in the list.  The
                         syntax without a preceding percent sign
                         ("**--trace** =**file** ") is deprecated.
    
                  **%process**
                  **process**
                         Traces system calls associated with process
                         lifecycle (creation, exec, termination).  The syntax
                         without a preceding percent sign ("**--trace** =**process** ")
                         is deprecated.
    
                  **%net**
                  **%network**
                  **network**
                         Traces all the network related system calls.  The
                         syntax without a preceding percent sign
                         ("**--trace** =**network** ") is deprecated.
    
                  **%signal**
                  **signal** Traces all signal related system calls.  The syntax
                         without a preceding percent sign ("**--trace** =**signal** ")
                         is deprecated.
    
                  **%ipc**
                  **ipc** Traces all IPC related system calls.  The syntax
                         without a preceding percent sign ("**--trace** =**ipc** ") is
                         deprecated.
    
                  **%desc**
                  **desc** Traces all file descriptor related system calls.
                         The syntax without a preceding percent sign
                         ("**--trace** =**desc** ") is deprecated.
    
                  **%memory**
                  **memory** Traces all memory mapping related system calls.  The
                         syntax without a preceding percent sign
                         ("**--trace** =**memory** ") is deprecated.
    
                  **%creds** Traces system calls that read or modify user and
                         group identifiers or capability sets.
    
                  **%stat** Traces stat system call variants.
    
                  **%lstat** Traces lstat system call variants.
    
                  **%fstat** Traces fstat, fstatat, and statx system call
                         variants.
    
                  **%%stat** Traces system calls used for requesting file status
                         (stat, lstat, fstat, fstatat, statx, and their
                         variants).
    
                  **%statfs**
                         Traces statfs, statfs64, statvfs, osf_statfs, and
                         osf_statfs64 system calls.  The same effect can be
                         achieved with **--trace** =**/^(.*_)?statv?fs** regular
                         expression.
    
                  **%fstatfs**
                         Traces fstatfs, fstatfs64, fstatvfs, osf_fstatfs,
                         and osf_fstatfs64 system calls.  The same effect can
                         be achieved with **--trace** =**/fstatv?fs** regular
                         expression.
    
                  **%%statfs**
                         Traces system calls related to file system
                         statistics (statfs-like, fstatfs-like, and ustat).
                         The same effect can be achieved with
                         **--trace** =**/statv?fs|fsstat|ustat** regular expression.
    
                  **%clock** Traces system calls that read or modify system
                         clocks.
    
                  **%pure** Traces system calls 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) 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-fd** =_set_
           **-e trace-fds** =_set_
           **-e fd** =_set_
           **-e fds** =_set_
           **--trace-fds** =_set_
                  Traces only the system calls that operate on the specified
                  subset of (non-negative) file descriptors.  Note that usage
                  of this option also filters out all the system calls that
                  do not operate on file descriptors at all.
    
                  This filter is combined with the **--trace-path** filter; a
                  system call is traced if it matches either of them.
    
           **-e signal** =_set_
           **-e signals** =_set_
           **-e s** =_set_
           **--signal** =_set_
                  Traces only the specified subset of signals.  The default
                  is **--signal** =**all**.  For example, **--signal** =!**SIGIO**(or
                  **--signal** =!**io**) causes **SIGIO** signals not to be traced.
    
           **-e status** =_set_
           **--status** =_set_
                  Prints only system calls with the specified return status.
                  The default is **--status** =**all**.  When using the **status**
                  qualifier, the chronological order of events may not be
                  preserved.  This is because **strace** must wait for a system
                  call to complete before deciding whether to print it.  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**
                         Traces system calls that returned without an error
                         code.  The **-z** option has the effect of
                         **--status** =**successful**.
                  **failed** Traces system calls that returned with an error
                         code.  The **-Z** option has the effect of
                         **--status** =**failed**.
                  **unfinished**
                         Traces system calls that did not return.  This might
                         happen, for example, due to an execve call in a
                         different thread from the same thread group.
                  **unavailable**
                         Traces system calls that returned but strace failed
                         to fetch the error status.
                  **detached**
                         Traces system calls for which strace detached before
                         the return.
    
           **-P** _path_
           **--trace-path** =_path_
                  Traces only system calls accessing _path_.  Multiple **-P**
                  options can be used to specify several paths.  This filter
                  is combined with the **--trace-fds** filter; a system call is
                  traced if it matches either option.
    
           **-z**
           **--successful-only**
                  Prints only system calls that returned without an error
                  code.
    
           **-Z**
           **--failed-only**
                  Prints only system calls that returned with an error code.
    
       **Output format**
           **-a** _column_
           **--columns** =_column_
                  Aligns return values in a specific column (default column
                  40).
    
           **-e abbrev** =_syscall_set_
           **-e a** =_syscall_set_
           **--abbrev** =_syscall_set_
                  Abbreviates the output from printing each member of large
                  structures.  The syntax of the _syscall_set_ specification is
                  the same as in the **--trace** option.  The default is
                  **--abbrev** =**all**.  The **-v** option has the effect of
                  **--abbrev** =**none**.
    
           **-e verbose** =_syscall_set_
           **-e v** =_syscall_set_
           **--verbose** =_syscall_set_
                  Dereferences structures for the specified set of system
                  calls.  The syntax of the _syscall_set_ specification is the
                  same as in the **--trace** option.  The default is
                  **--verbose** =**all**.
    
           **-e raw** =_syscall_set_
           **-e x** =_syscall_set_
           **--raw** =_syscall_set_
                  Prints raw, undecoded arguments for the specified set of
                  system calls.  The syntax of the _syscall_set_ specification
                  is the same as in the **--trace** option.  This option has the
                  effect of causing all arguments to be printed in
                  hexadecimal.  This option is useful if the decoding is not
                  trusted, or if the actual numeric value of an argument is
                  needed.  See also **-X raw** option.
    
           **-e read** =_set_
           **-e reads** =_set_
           **-e r** =_set_
           **--read** =_set_
                  Performs 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 **--read** =_3_ ,_5_.  Note that this is independent from
                  the normal tracing of the read(2) system call that is
                  controlled by the option **--trace** =**read**.
    
           **-e write** =_set_
           **-e writes** =_set_
           **-e w** =_set_
           **--write** =_set_
                  Performs 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 **--write** =_3_ ,_5_.  Note that this is independent
                  from the normal tracing of the write(2) system call that is
                  controlled by the option **--trace** =**write**.
    
           **-e quiet** =_set_
           **-e silent** =_set_
           **-e silence** =_set_
           **-e q** =_set_
           **--quiet** =_set_
           **--silent** =_set_
           **--silence** =_set_
                  Suppresses various information messages.  The default is
                  **--quiet** =**none**.  _set_ can include the following elements:
    
                  **attach** Suppresses messages about attaching and detaching
                         ("**[ Process NNNN attached ]** ", "**[ Process NNNN**
                         **detached ]** ").
                  **exit** Suppress messages about process exits ("**+++ exited**
                         **with SSS +++** ").
                  **path-resolution**
                         Suppress messages about resolution of paths provided
                         via the **-P** option ("**Requested path "..." resolved**
                         **into "..."** ").
                  **personality**
                         Suppress messages about process personality changes
                         ("**[ Process PID=NNNN runs in PPP mode. ]** ").
                  **thread-execve**
                  **superseded**
                         Suppress messages about process being superseded by
                         execve(2) in another thread ("**+++ superseded by**
                         **execve in pid NNNN +++** ").
    
           **-e decode-fds** =_set_
           **--decode-fds** =_set_
                  Decodes various information associated with file
                  descriptors.  The default is **--decode-fds** =**none**.  _set_ can
                  include the following elements:
    
                  **path** Prints file paths.  Also enables printing of
                           tracee's current working directory when **AT_FDCWD**
                           constant is used.
                  **socket** Prints socket protocol-specific information.
                  **dev** Prints character/block device numbers.
                  **eventfd** Prints eventfd object details associated with
                           eventfd file descriptors.
                  **pidfd** Prints PIDs associated with pidfd file
                           descriptors.
                  **signalfd** Prints signal masks associated with signalfd file
                           descriptors.
    
           **-e decode-pids** =_set_
           **--decode-pids** =_set_
                  Decodes various information associated with process IDs
                  (and also thread IDs, process group IDs, and session IDs).
                  The default is **--decode-pids** =**none**.  _set_ can include the
                  following elements:
    
                  **comm** Prints command names associated with thread or
                          process IDs.
                  **pidns** Prints thread, process, process group, and session
                          IDs in strace's PID namespace if the tracee is in a
                          different PID namespace.
    
           **-e kvm** =**vcpu**
           **--kvm** =**vcpu**
                  Prints the exit reason of kvm vcpu.  Requires Linux kernel
                  version 4.16.0 or higher.
    
           **-e namespace** =**new**
           **--namespace** =**new**
                  Prints the new namespaces entered by the tracee.  The
                  following system calls are supported: clone(2), clone3(2),
                  setns(2), and unshare(2).
    
           **-i**
           **--instruction-pointer**
                  Prints the instruction pointer at the time of the system
                  call.
    
           **-n**
           **--syscall-number**
                  Prints the system call number.
    
           **-N**
           **--arg-names**
                  Prints the system call argument names.
    
           **-k**
           **--stack-trace**[=**symbol**]
                  Prints the execution stack trace of the traced processes
                  after each system call.
    
           **-kk**
           **--stack-trace** =**source**
                  Prints the execution stack trace and source code
                  information of the traced processes after each system call.
                  This option expects the target program is compiled with
                  appropriate debug options: "-g" (gcc), or "-g
                  -gdwarf-aranges" (clang).
    
           **--stack-trace-frame-limit** =_limit_
                  Prints no more than this amount of stack trace frames when
                  backtracing a system call (the default is 256).  Use this
                  option with the **--stack-trace**(or **-k**) option.
    
           **-o** _filename_
           **--output** =_filename_
                  Writes 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.  Piping output to a command is not
                  currently compatible with the **-ff** option.
    
           **-A**
           **--output-append-mode**
                  Opens the file provided in the **-o** option in append mode.
    
           **-q**
           **--quiet**
           **--quiet** =**attach** ,**personality**
                  Suppresses messages about attaching, detaching, and
                  personality changes.  This happens automatically when
                  output is redirected to a file and the command is run
                  directly instead of attaching.
    
           **-qq**
           **--quiet** =**attach** ,**personality** ,**exit**
                  Suppresses messages about attaching, detaching, personality
                  changes, and process exit status.
    
           **-qqq**
           **--quiet** =**all**
                  Suppresses all suppressible messages (please refer to the
                  **--quiet** option description for the full list of
                  suppressible messages).
    
           **-r**
           **--relative-timestamps**[=_precision_]
                  Prints a relative timestamp upon entry to each system call.
                  This records the time difference between the beginning of
                  successive system calls.  _precision_ can be one of **s**(for
                  seconds), **ms**(milliseconds), **us**(microseconds), or **ns**
                  (nanoseconds), and allows setting the precision of time
                  value being printed.  Default is **us**(microseconds).  Note
                  that because the **-r** option uses the monotonic clock, its
                  measurements may differ from the time differences reported
                  by the **-t** option, which uses the wall clock.
    
           **-s** _strsize_
           **--string-limit** =_strsize_
                  Specifies the maximum string size to print (the default is
                  32).  Note that filenames are not considered strings and
                  are always printed in full.
    
           **--absolute-timestamps**[=[[**format:**]_format_],[[**precision:**]_precision_]]
           **--timestamps**[=[[**format:**]_format_],[[**precision:**]_precision_]]
                  Prefixes each line of the trace with the wall clock time in
                  the specified _format_ with the specified _precision_.  _format_
                  can be one of the following:
    
                  **none** No time stamp is printed.  Can be used to override
                         the previous setting.
                  **time** Wall clock time (strftime(3) format string is **%T**).
                  **unix** Number of seconds since the epoch (strftime(3)
                         format string is **%s**).
    
                  _precision_ can be one of **s**(for seconds), **ms**(milliseconds),
                  **us**(microseconds), or **ns**(nanoseconds).  Default arguments
                  for the option are **format:time** ,**precision:s**.
    
           **-t**
           **--absolute-timestamps**
                  Prefixes each line of the trace with the wall clock time.
    
           **-tt**
           **--absolute-timestamps** =**precision:us**
                  Prints the wall clock time with microsecond precision.
    
           **-ttt**
           **--absolute-timestamps** =**format:unix** ,**precision:us**
                  Prints the wall clock time as seconds since the epoch, with
                  microsecond precision.
    
           **-T**
           **--syscall-times**[=_precision_]
                  Shows the time spent in system calls.  This records the
                  time difference between the beginning and the end of each
                  system call.  _precision_ can be one of **s**(for seconds), **ms**
                  (milliseconds), **us**(microseconds), or **ns**(nanoseconds), and
                  allows setting the precision of time value being printed.
                  Default is **us**(microseconds).
    
           **-v**
           **--no-abbrev**
                  Prints unabbreviated versions of environment, stat,
                  termios, etc. calls.  These structures are very common, so
                  the default behavior is to display a reasonable subset of
                  their members.  Use this option to see all members in full
                  detail.
    
           **--strings-in-hex**[=_option_]
                  Controls the use of hexadecimal escape sequences when
                  printing strings.  This option alters the default escaping
                  behavior.
    
                  Normally (when neither this option nor -x is used), **strace**
                  introduces escape sequences in two situations: to represent
                  non-printable and non-ASCII characters (i.e., those with
                  character codes less than 32 or greater than 127), or to
                  disambiguate output, for example, by escaping the quotation
                  marks that enclose a string or the angle brackets used in
                  file descriptor paths.  When a character must be escaped,
                  **strace** prioritizes symbolic C-standard sequences if one
                  exists: “**\t** ” (tab), “**\n** ” (newline), “**\v** ” (vertical tab),
                  “**\f** ” (form feed), and “**\r** ” (carriage return).  For all
                  other characters that require escaping, **strace** defaults to
                  using an octal representation of the character's byte
                  value.  This option allows you to override this default
                  behavior and use hexadecimal escapes instead of octal ones.
    
                  _option_ can be one of the following:
    
                  **none** Hexadecimal numbers are not used in the output at
                         all.  When there is a need to emit an escape
                         sequence, octal numbers are used.
                  **non-ascii-chars**
                         Hexadecimal numbers are used instead of octal in the
                         escape sequences.
                  **non-ascii**
                         Strings that contain non-ASCII characters are
                         printed using escape sequences with hexadecimal
                         numbers.
                  **all** All strings are printed using escape sequences with
                         hexadecimal numbers.
    
                  When the option is supplied without an argument, **all** is
                  assumed.
    
           **-x**
           **--strings-in-hex** =**non-ascii**
                  Prints all non-ASCII strings in hexadecimal string format.
    
           **-xx**
           **--strings-in-hex**[=**all**]
                  Prints all strings in hexadecimal string format.
    
           **-X** _format_
           **--const-print-style** =_format_
                  Sets the format for printing of named constants and flags.
                  Supported _format_ values are:
    
                  **raw** Raw number output, without decoding.
                  **abbrev** Outputs a named constant or a set of flags instead
                         of the raw number if they are found.  This is the
                         default **strace** behaviour.
                  **verbose**
                         Outputs both the raw value and the decoded string
                         (as a comment).
    
           **-y**
           **--decode-fds**
           **--decode-fds** =**path**
                  Prints paths associated with file descriptor arguments and
                  with the **AT_FDCWD** constant.
    
           **-yy**
           **--decode-fds** =**all**
                  Prints all available information associated with file
                  descriptors: protocol-specific information associated with
                  socket file descriptors, block/character device number
                  associated with device file descriptors, and PIDs
                  associated with pidfd file descriptors.
    
           **--pidns-translation**
           **--decode-pids** =**pidns**
                  If strace and tracee are in different PID namespaces, print
                  PIDs in strace's namespace, too.
    
           **-Y**
           **--decode-pids** =**comm**
                  Prints command names for PIDs.
    
           **--secontext**[=_format_]
           **-e secontext** =_format_
                  When SELinux is available and is not disabled, prints in
                  square brackets SELinux contexts of processes, files, and
                  descriptors.  The _format_ argument is a comma-separated list
                  of items being one of the following:
    
                  **full** Prints the full context (user, role, type
                                    level and category).
                  **mismatch** Also prints the context recorded by the
                                    SELinux database in case the current
                                    context differs.  The latter is printed
                                    after two exclamation marks (!!).
    
                  The default value for **--secontext** is **!full,mismatch** that
                  prints only the type instead of full context and doesn't
                  check for context mismatches.
    
           **--always-show-pid**
                  Shows PID prefix also for the process started by strace.
                  Implied when -f and -o are both specified.
    
       **Statistics**
           **-c**
           **--summary-only**
                  Counts time, calls, and errors for each system call and
                  report a summary on program exit, suppressing the regular
                  output.  This shows system time (CPU time spent in the
                  kernel), which is independent of wall clock time.  If **-c** is
                  used with **-f** , only aggregate totals for all traced
                  processes are kept.
    
           **-C**
           **--summary**
                  Like **-c** , but also prints the regular output while processes
                  are running.
    
           **-O** _overhead_
           **--summary-syscall-overhead** =_overhead_
                  Sets the overhead for tracing system calls to _overhead_.
                  This is useful for overriding the default heuristic, which
                  estimates the time spent in the measurement process itself
                  when timing system calls with 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_
           **--summary-sort-by** =_sortby_
                  Sorts the output of the histogram printed by the **-c** option
                  by the specified criterion.  Valid values are **time**(or
                  **time-percent** or **time-total** or **total-time**), **min-time**(or
                  **shortest** or **time-min**), **max-time**(or **longest** or **time-max**),
                  **avg-time**(or **time-avg**), **calls**(or **count**), **errors**(or
                  **error**), **name**(or **syscall** or **syscall-name**), and **nothing**(or
                  **none**); default is **time**.
    
           **-U** _columns_
           **--summary-columns** =_columns_
                  Configures the set and order of columns shown in the call
                  summary.  The _columns_ argument is a comma-separated list
                  containing one or more of the following values:
    
                  **time-percent**(or **time**)
                         Percentage of cumulative time consumed by a specific
                         system call.
                  **total-time**(or **time-total**)
                         Total system (or wall clock, if **-w** option is
                         provided) time consumed by a specific system call.
                  **min-time**(or **shortest** or **time-min**)
                         Minimum observed call duration.
                  **max-time**(or **longest** or **time-max**)
                         Maximum observed call duration.
                  **avg-time**(or **time-avg**)
                         Average call duration.
                  **calls**(or **count**)
                         Call count.
                  **errors**(or **error**)
                         Error count.
                  **name**(or **syscall** or **syscall-name**)
                         System call name.
    
                  The default value is
                  **time-percent** ,**total-time** ,**avg-time** ,**calls** ,**errors** ,**name**.  If the
                  **name** field is not supplied explicitly, it is added as the
                  last column.
    
           **-w**
           **--summary-wall-clock**
                  Summarizes the wall clock time for each system call,
                  measured from its beginning to its end.  The default is to
                  summarize the system time.
    
       **Tampering**
           **--inject** =_syscall_set_[:**error** =_errno_ |:**retval** =_value_][:**signal** =_sig_]
           [:**syscall** =_syscall_][:**delay_enter** =_delay_][:**delay_exit** =_delay_]
           [:**poke_enter** =_@argN=DATAN,@argM=DATAM..._]
           [:**poke_exit** =_@argN=DATAN,@argM=DATAM..._][:**when** =_expr_]
                  Performs  system  call  tampering  for the specified set of
                  system calls.
    
                  The syntax of the _syscall_set_ specification is the same  as
                  in the **--trace** option.
    
                  At   least  one  of  **error** ,  **retval** ,  **signal** ,  **delay_enter** ,
                  **delay_exit** , **poke_enter** , or **poke_exit** action options must be
                  specified.  **error** and **retval** are mutually exclusive.
    
                  If the **error** =_errno_ option is specified, a fault is injected
                  into the system call.  This is achieved  by  replacing  the
                  system  call number with -1 (representing an invalid system
                  call) and setting the error code to  the  specified  _errno_.
                  This  behavior  of replacing the syscall number with -1 can
                  be overridden using the **syscall** = option.  The _errno_ can  be
                  a symbolic name like **ENOSYS** or a numeric value in the range
                  1..4095.
    
                  If the **retval** =_value_ option is specified, a success value is
                  injected.   The  system call number is replaced as with the
                  **error** = option, but  instead  of  an  error,  the  specified
                  success _value_ is returned to the caller process.
    
                  If  the  **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 system call specified by the _syscall_set_.
    
                  If the **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 system call, respectively.  The format of _delay_
                  specification  is  described  in section _Time specification_
                  _format description_.
    
                  If    the     **poke_enter** =_@argN=DATAN,@argM=DATAM..._      or
                  **poke_exit** =_@argN=DATAN,@argM=DATAM..._ options are specified,
                  tracee's  memory  at  locations,  pointed to by system call
                  arguments _argN_ and  _argM_  (going  from  _arg1_  to  _arg7_)  is
                  overwritten   by   data   _DATAN_  and  _DATAM_  (specified  in
                  hexadecimal          format;          for           example
                  **poke_enter** =_@arg1=0000DEAD0000BEEF_).   The **poke_enter** option
                  modifies memory on system call enter, while **poke_exit** does
                  so on system call exit.
    
                  The   injection  actions  are  independent.   For  example,
                  specifying only **signal** = delivers a signal without  altering
                  the  system  call's  outcome  or  delaying  it.  Similarly,
                  specifying only **error** = injects a system call fault  without
                  adding a signal or delay.
    
                  If   the  **signal** =_sig_  option  is  specified  together  with
                  **error** =_errno_ or **retval** =_value_ , then both injection of a fault
                  or success and signal delivery are performed.
    
                  If the  **syscall** =_syscall_  option  is  specified,  the  given
                  _syscall_  is  injected  instead  of  the  default  -1.   The
                  specified _syscall_ must have  no  side  effects;  currently,
                  only system calls from the **%pure** set are supported.
    
                  Unless   the   **when** =_expr_  subexpression  is  specified,  an
                  injection is being  made  into  every  invocation  of  each
                  system call from the _syscall_set_.
    
                  The format of the subexpression is:
    
                                 _first_[**..**_last_][**+**[_step_]]
    
                  Number  _first_ stands for the first invocation number in the
                  range, number _last_ stands for the last invocation number in
                  the range,  and  _step_  stands  for  the  step  between  two
                  consecutive  invocations.   The  following combinations are
                  useful:
    
                  _first_  Injects into invocation number _first_ only for each
                         system call in the _syscall_set_.
                  _first_**..**_last_
                         Injects into invocations from _first_ through _last_
                         (inclusive) for each system call in the _syscall_set_.
                  _first_**+** Injects into every invocation, starting with number
                         _first_ , for each system call in the _syscall_set_.
                  _first_**+**_step_
                         Injects into invocations number _first_ , _first_ +_step_ ,
                         _first_ +_step_ +_step_ , and so on, for each system call in
                         the _syscall_set_.
                  _first_**..**_last_**+**_step_
                         Same as the previous, but consider only invocations
                         with numbers up to _last_ (inclusive).
    
                  For example, to fail each third and subsequent chdir system
                  calls with **ENOENT** , use **--inject** =_chdir_ :**error** =_ENOENT_ :**when** =_3_**+**.
    
                  The valid range for numbers _first_ and _step_ is 1..65535, and
                  for number _last_ is 1..65534.
    
                  An injection expression can contain at most one fault or
                  return value specification (i.e., either **error** = or **retval** =)
                  and at most one **signal** = specification.  If an injection
                  expression contains multiple **when** = specifications, the last
                  one takes precedence.
    
                  Accounting of system calls that are subject to injection is
                  done per system call and per tracee.
    
                  Specification of system call injection can be combined with
                  other system call filtering options, for example, **-P**
                  _/dev/urandom_ **--inject** =_file_ :**error** =_ENOENT_.
    
           **-e inject** =_args_
                  This is equivalent to **--inject** =_args_.
    
           **--fault** =_syscall_set_[:**error** =_errno_][:**when** =_expr_]
                  Performs system call fault injection for the specified set
                  of system calls.
    
                  This is a shortcut for the more general **--inject** = option,
                  using a default _errno_ of **ENOSYS**.
    
           **-e fault** =_args_
                  This is equivalent to **--fault** =_args_.
    
       **Miscellaneous**
           **-d**
           **--debug**
                  Shows 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.
                  Using multiple **-F** options is equivalent to a single **-f**.
                  This option is ignored entirely if used in conjunction with
                  one or more **-f** options.
    
           **-h**
           **--help** Prints the help summary.
    
           **--seccomp-bpf**
                  Attempts to use seccomp-bpf (see seccomp(2)) to cause the
                  kernel to stop the tracee only for the system calls that
                  are being traced.
    
                  This option has no effect unless **-f** /**--follow-forks** is also
                  specified.  **--seccomp-bpf** is not compatible with
                  **--syscall-limit** and **-b** /**--detach-on** options.  It is also not
                  applicable to processes attached using **-p** /**--attach** option.
    
                  An attempt to enable system calls filtering using seccomp-
                  bpf 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.  If the seccomp-bpf
                  filter setup fails, **strace** proceeds as usual, stopping
                  traced processes on every system call.
    
                  When **--seccomp-bpf** is activated and **-p** /**--attach** option is
                  not used, **--kill-on-exit** option is activated as well.
    
                  Note that in cases when the tracee has another seccomp
                  filter that returns an action value with a precedence
                  greater than **SECCOMP_RET_TRACE** , **strace --seccomp-bpf** will
                  not be notified.  That is, if another seccomp filter, for
                  example, disables the system call or kills the tracee, then
                  **strace --seccomp-bpf** will not be aware of that system call
                  invocation at all.
    
           **--tips**[=[[**id:**]_id_],[[**format:**]_format_]]
                  Shows strace tips, tricks, and tweaks before exit.  The _id_
                  can be a non-negative integer to print a specific tip
                  (note: these IDs are not guaranteed to be stable).  It can
                  also be **random**(the default), in which case a random tip is
                  printed.  _format_ can be one of the following:
    
                  **none** No tip is printed.  Can be used to override the
                           previous setting.
                  **compact** Prints the tip just big enough to contain all the
                           text.
                  **full** Prints the tip in its full glory.
    
                  Default is **id:random,format:compact**.
    
           **-V**
           **--version**
                  Prints the version number of **strace** and the list of enabled
                  optional features.  Multiple instances of this option
                  beyond specific threshold tend to increase der Strauss
                  awareness.
    
       **Time specification format description**
           Time values are specified as a decimal floating point number (in a
           format accepted by strtod(3)), optionally followed by a suffix to
           indicate the unit of time: **s**(seconds), **ms**(milliseconds), **us**
           (microseconds), or **ns**(nanoseconds).  If no suffix is specified,
           the value defaults to microseconds.
    
           The described format is used for **-O** , **--inject** =**delay_enter** , and
           **--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 the parent-
           child relationship (signal stop notifications, the getppid(2)
           value, etc) between the traced process and its parent is not
           preserved unless **-D** is used.
    
           When using **-p** without a _command_ , the exit status of **strace** is zero
           unless no processes have been attached or an unexpected error
           occurred during 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 these capabilities
           should only be granted to users with full root privileges,
           installing **strace** as setuid to root is only appropriate when its
           use is restricted to such trusted users.  For example, a special
           version of **strace** could be installed with mode 'rwsr-x---', user
           **root,** and group **trace**.  In this configuration, only trusted users
           who are members of the **trace** group could execute it.  If you use
           this feature, remember to also install a regular, non-setuid
           version of **strace** for ordinary users.
    


## MULTIPLE PERSONALITIES SUPPORT



           On some architectures, **strace** can decode system calls for
           processes that use a different Application Binary Interface (ABI)
           from 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 depends on the ability to generate
           and parse structure definitions at build time.  Refer to the
           output of the **strace -V** command to determine which ABIs are
           supported by your **strace** build.  In this context, "non-native"
           refers to an ABI that differs from the one **strace** is using:
    
           **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** , it
           means that support for decoding non-native 32-bit binaries is not
           applicable to the architecture.
    
           Likewise, if the output contains neither **mx32-mpers** nor
           **no-mx32-mpers** , it means that support for decoding non-native
           32-on-64-bit binaries is not applicable to the architecture.
    


## NOTES



           Systems that use shared libraries often produce a large amount of
           tracing output when loading them.
    
           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 underlying
           faccessat(2) system call does not have a _flags_ argument, and the
           setrlimit(2) library function is implemented using prlimit64(2)
           system call on modern (2.6.38+) kernels.  These discrepancies are
           normal characteristics of the system call interface and are
           handled 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
           system call and **xtensa_fadvise64_64**(2) Xtensa system call are
           filtered and printed as fadvise64_64(2).
    
           On the x32 ABI, some system calls are intended for 64-bit
           processes but can be invoked from x32 by setting the
           **__X32_SYSCALL_BIT** flag.  When this occurs, **strace** designates these
           calls with a **#64** suffix.  An example is readv(2), which is syscall
           number 19 on x86_64, whereas its distinct x32 counterpart is
           syscall number 515.
    
           On some platforms, a process attached with the **-p** option may
           receive a spurious **EINTR** error from a non-restartable system call.
           This can have an unpredictable effect on the process if it does
           not attempt to restart the call.  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.
    
           Since **strace** executes the specified _command_ directly without a
           shell, scripts that lack a shebang line (e.g., #!/bin/sh) will
           fail with an **ENOEXEC** error, even if a shell could run them
           correctly.  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 more slowly than a non-traced one.  The
           performance impact can be mitigated by using the **--seccomp-bpf**
           option.
    
           When tracing a _command_ , its descendant processes may be left
           running after **strace** is terminated by an interrupt signal (such as
           CTRL-C**).** This can be prevented by using the **--kill-on-exit**
           option, or by using **--seccomp-bpf** option in a way that implies
           **--kill-on-exit**.
    
           A traced process can use the **CLONE_UNTRACED** flag with the **clone**
           system call to create a child process that is not traced by
           strace.  This breaks a guarantee of the **--seccomp-bpf** option, as
           this untraced child may be left with an active seccomp filter
           after strace terminates.
    


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