path: root/doc/strace.1.in

.\" Copyright (c) 1991, 1992 Paul Kranenburg <pk@cs.few.eur.nl>
.\" Copyright (c) 1993 Branko Lankester <branko@hacktic.nl>
.\" Copyright (c) 1993, 1994, 1995, 1996 Rick Sladkey <jrs@world.std.com>
.\" Copyright (c) 1996-2021 The strace developers.
.\" All rights reserved.
.\"
.\" SPDX-License-Identifier: LGPL-2.1-or-later
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.TH STRACE 1 "@STRACE_MANPAGE_DATE@" "strace @VERSION@"
.SH NAME
strace \- trace system calls and signals
.SH SYNOPSIS
.SY strace
.if '@ENABLE_STACKTRACE_FALSE@'#' .OP \-ACdffhikqqrtttTvVwxxyyYzZ
.if '@ENABLE_STACKTRACE_TRUE@'#' .OP \-ACdffhiqqrtttTvVwxxyyYzZ
.OP \-a column
.OP \-b execve
.OM \-e expr
.OP \-I n
.OP \-o file
.OP \-O overhead
.OM \-p pid
.OM \-P path
.OP \-s strsize
.OP \-S sortby
.OP \-U columns
.OP \-X format
.OP \-\-seccomp\-bpf
.OP \-\-syscall\-limit limit
.if '@ENABLE_SECONTEXT_FALSE@'#' .OP \-\-secontext\fR[=\fIformat\fR]
.OP \-\-tips\fR[=\fIformat\fR]
.BR "" {
.OR \-p pid
.BR "" |
.OP \-DDD
.OM \-E var\fR[=\fIval\fR]
.OP \-u username
.IR command " [" args ]
.BR "" }
.YS
.SY strace
.B \-c
.OP \-dfwzZ
.OP \-b execve
.OM \-e expr
.OP \-I n
.OP \-O overhead
.OM \-p pid
.OM \-P path
.OP \-S sortby
.OP \-U columns
.OP \-\-seccomp\-bpf
.OP \-\-syscall\-limit limit
.OP \-\-tips\fR[=\fIformat\fR]
.BR "" {
.OR \-p pid
.BR "" |
.OP \-DDD
.OM \-E var\fR[=\fIval\fR]
.OP -u username
.IR command " [" args ]
.BR "" }
.YS
.SY strace
.B \-\-tips\fR[=\fIformat\fR]
.YS
.SH DESCRIPTION
.IX "strace command" "" "\fLstrace\fR command"
.LP
In the simplest case
.B strace
runs the specified
.I 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
.B \-o
option.
.LP
.B 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.
.LP
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:
.CW
open("/dev/null", O_RDONLY) = 3
.CE
Errors (typically a return value of \-1) have the errno symbol
and error string appended.
.CW
open("/foo/bar", O_RDONLY) = \-1 ENOENT (No such file or directory)
.CE
Signals are printed as signal symbol and decoded siginfo structure.
An excerpt from stracing and interrupting the command "sleep 666" is:
.CW
sigsuspend([] <unfinished ...>
--- SIGINT {si_signo=SIGINT, si_code=SI_USER, si_pid=...} ---
+++ killed by SIGINT +++
.CE
If a system call is being executed and meanwhile another one is being called
from a different thread/process then
.B strace
will try to preserve the order of those events and mark the ongoing call as
being
.IR unfinished .
When the call returns it will be marked as
.IR resumed .
.CW
[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])
.CE
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.
.CW
read(0, 0x7ffff72cf5cf, 1)              = ? ERESTARTSYS (To be restarted)
--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn({mask=[]})                 = 0
read(0, "", 1)                          = 0
.CE
Arguments are printed in symbolic form with passion.
This example shows the shell performing ">>xyzzy" output redirection:
.CW
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
.CE
Here, the second and the third argument of
.BR open (2)
are 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,
.B strace
output is proven to be more readable than the source.
.LP
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:
.CW
lstat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x3), ...}) = 0
.CE
Notice how the 'struct stat' argument is dereferenced and how each member is
displayed symbolically.  In particular, observe how the
.B 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
.BR 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:
.CW
lstat("/foo/bar", 0xb004) = \-1 ENOENT (No such file or directory)
.CE
In this case the porch light is on but nobody is home.
.LP
Syscalls unknown to
.B strace
are printed raw, with the unknown system call number printed in hexadecimal form
and prefixed with "syscall_":
.CW
syscall_0xbad(0x1, 0x2, 0x3, 0x4, 0x5, 0x6) = -1 ENOSYS (Function not implemented)
.CE
.LP
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
.I 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
.BR getpwuid (3)
library routine is reading the password file:
.CW
read(3, "root::0:0:System Administrator:/"..., 1024) = 422
.CE
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
.BR id (1)
on a system with supplementary group ids:
.CW
getgroups(32, [100, 0]) = 2
.CE
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:
.CW
sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0
.CE
Here, the second argument is a bit-set of two signals,
.BR 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:
.CW
sigprocmask(SIG_UNBLOCK, ~[], NULL) = 0
.CE
Here, the second argument represents the full set of all signals.
.SH OPTIONS
.SS General
.TP 12
.BI "\-e " expr
A qualifying expression which modifies which events to trace
or how to trace them.  The format of the expression is:
.RS 15
.IP
[\,\fIqualifier\/\fB=\fR][\fB!\fR]\,\fIvalue\/\fR[\fB,\fR\,\fIvalue\/\fR]...
.RE
.IP
where
.I qualifier
is one of
.BR trace " (or " t ),
.BR trace\-fds " (or " trace\-fd " or " fd " or " fds ),
.BR abbrev " (or " a ),
.BR verbose " (or " v ),
.BR raw " (or " x ),
.BR signal " (or " signals " or " s ),
.BR read " (or " reads " or " r ),
.BR write " (or " writes " or " w ),
.BR fault ,
.BR inject ,
.BR status ,
.BR quiet " (or " silent " or " silence " or " q ),
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR secontext ,
.BR decode\-fds " (or " decode\-fd ),
.BR decode\-pids " (or " decode\-pid ),
or
.BR kvm ,
and
.I value
is a qualifier-dependent symbol or number.  The default
qualifier is
.BR trace .
Using an exclamation mark negates the set of values.  For example,
.BR \-e "\ " open
means literally
.BR \-e "\ " trace = open
which in turn means trace only the
.B open
system call.  By contrast,
.BR \-e "\ " trace "=!" open
means to trace every system call except
.BR open .
In addition, the special values
.B all
and
.B none
have the obvious meanings.
.IP
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.
.SS Startup
.TP 12
\fB\-E\ \fIvar\fR=\,\fIval\fR
.TQ
.BR "\-\-env" = \fIvar\fR = \fIval\fR
Run command with
.IR var = val
in its list of environment variables.
.TP
.BI "\-E " var
.TQ
.BR "\-\-env" = \fIvar\fR
Remove
.IR var
from the inherited list of environment variables before passing it on to
the command.
.TP
.BI "\-p " pid
.TQ
.BR "\-\-attach" = \fIpid\fR
Attach to the process with the process
.SM ID
.I pid
and begin tracing.
The trace may be terminated
at any time by a keyboard interrupt signal
.RB ( CTRL\-C ).
.B strace
will respond by detaching itself from the traced process(es)
leaving it (them) to continue running.
Multiple
.B \-p
options can be used to attach to many processes in addition to
.I command
(which is optional if at least one
.B \-p
option is given).
Multiple process IDs, separated by either
comma (\(lq,\(rq), space (\(lq \(rq), tab, or newline character,
can be provided as an argument to a single
.B \-p
option, so, for example,
.B \-p
"$(pidof PROG)" and
.B \-p
"$(pgrep PROG)" syntaxes are supported.
.TP
.BI "\-u " username
.TQ
.BR "\-\-user" = \fIusername\fR
Run command with the user \s-1ID\s0, group \s-2ID\s0, and
supplementary groups of
.IR 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.
.SS Tracing
.TP 12
.BI "\-b " syscall
.TQ
.BR "\-\-detach\-on" = \fIsyscall\fR
If specified syscall is reached, detach from traced process.
Currently, only
.BR execve (2)
syscall is supported.  This option is useful if you want to trace
multi-threaded process and therefore require
.BR \-f ,
but don't want to trace its (potentially very complex) children.
.TP
.B \-D
.TQ
.B \-\-daemonize
.TQ
.BR \-\-daemonize = grandchild
Run tracer process as a grandchild, not as the parent of the
tracee.  This reduces the visible effect of
.B strace
by keeping the tracee a direct child of the calling process.
.TP
.B \-DD
.TQ
.BR \-\-daemonize = pgroup
.TQ
.BR \-\-daemonize = pgrp
Run tracer process as tracee's grandchild in a separate process group.
In addition to reduction of the visible effect of
.BR strace ,
it also avoids killing of
.B strace
with
.BR kill (2)
issued to the whole process group.
.TP
.B \-DDD
.TQ
.BR \-\-daemonize = session
Run tracer process as tracee's grandchild in a separate session
("true daemonisation").
In addition to reduction of the visible effect of
.BR strace ,
it also avoids killing of
.B strace
upon session termination.
.TP
.B \-f
.TQ
.BR \-\-follow\-forks
Trace child processes as they are created by currently traced
processes as a result of the
.BR fork (2),
.BR vfork (2)
and
.BR clone (2)
system calls.  Note that
.B \-p
.I PID
.B \-f
will attach all threads of process
.I PID
if it is multi-threaded, not only thread with
.IR thread_id " = " PID .
.TP
.B \-\-output\-separately
If the
.BR \-\-output = \fIfilename\fR
option is in effect, each processes trace is written to
.IR filename . pid
where
.I pid
is the numeric process id of each process.
.TP
.B \-ff
.TQ
.B \-\-follow\-forks \-\-output\-separately
Combine the effects of
.B \-\-follow\-forks
and
.B \-\-output\-separately
options.
This is incompatible with
.BR \-c ,
since no per-process counts are kept.
.IP
One might want to consider using
.BR strace-log-merge (1)
to obtain a combined strace log view.
.TP
.BI "\-I " interruptible
.TQ
.BR "\-\-interruptible" = \fIinterruptible\fR
When
.B strace
can be interrupted by signals (such as pressing
.BR CTRL\-C ).
.RS
.TP 15
.BR 1 ", " anywhere
no signals are blocked;
.TQ
.BR 2 ", " waiting
fatal signals are blocked while decoding syscall (default);
.TQ
.BR 3 ", " never
fatal signals are always blocked (default if
.BR -o " " \fIFILE\fR " " \fIPROG\fR );
.TQ
.BR 4 ", " never_tstp
fatal signals and
.BR SIGTSTP " (" CTRL\-Z )
are always blocked (useful to make
.BI "strace -o " "FILE PROG"
not stop on
.BR CTRL\-Z ,
default if
.BR \-D ).
.RE
.TP
.BR "\-\-syscall\-limit" = \fIlimit\fR
Detach all tracees when
.I limit
number of syscalls have been captured. Syscalls filtered out via
.BR \-\-trace ,
.B \-\-trace\-path
or
.B \-\-status
options are not considered when keeping track of the number of syscalls that are captured.
.SS Filtering
.TP 12
\fB\-e\ trace\fR=\,\fIsyscall_set\fR
.TQ
\fB\-e\ t\fR=\,\fIsyscall_set\fR
.TQ
\fB\-\-trace\fR=\,\fIsyscall_set\fR
Trace only the specified set of system calls.
.I syscall_set
is defined as
[\fB!\fR]\,\fIvalue\fR[\fB,\fR\,\fIvalue\/\fR],
and
.I value
can be one of the following:
.RS
.TP 13
.I syscall
Trace specific syscall, specified by its name (see
.BR syscalls (2)
for a reference, but also see
.BR NOTES ).
.TP
.BI ? value
Question mark before the syscall qualification allows suppression of error
in case no syscalls matched the qualification provided.
.TP
.IB value @64
Limit the syscall specification described by
.I value
to 64-bit personality.
.TP
.IB value @32
Limit the syscall specification described by
.I value
to 32-bit personality.
.TP
.IB value @x32
Limit the syscall specification described by
.I value
to x32 personality.
.TP
.B all
Trace all system calls.
.TP
.BI / regex
Trace only those system calls that match the
.IR regex .
You can use
.B POSIX
Extended Regular Expression syntax (see
.BR regex (7)).
.TP
.B %file
.TQ
.BR file
Trace all system calls which take a file name as an argument.  You
can think of this as an abbreviation for
.BR "\-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
.BR lstat (2)
in the list.  Betchya woulda forgot that one.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = file \[dq])
is deprecated.
.TP
.B %process
.TQ
.B process
Trace system calls associated with process lifecycle
(creation, exec, termination).
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = process \[dq])
is deprecated.
.TP
.B %net
.TQ
.B %network
.TQ
.B network
Trace all the network related system calls.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = network \[dq])
is deprecated.
.TP
.BR %signal
.TQ
.BR signal
Trace all signal related system calls.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = signal \[dq])
is deprecated.
.TP
.BR %ipc
.TQ
.BR ipc
Trace all IPC related system calls.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = ipc \[dq])
is deprecated.
.TP
.BR %desc
.TQ
.BR desc
Trace all file descriptor related system calls.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = desc \[dq])
is deprecated.
.TP
.BR %memory
.TQ
.BR memory
Trace all memory mapping related system calls.
The syntax without a preceding percent sign
.RB (\[dq] "-e trace" = memory \[dq])
is deprecated.
.TP
.BR %creds
Trace system calls that read or modify user and group identifiers or capability sets.
.TP
.BR %stat
Trace stat syscall variants.
.TP
.BR %lstat
Trace lstat syscall variants.
.TP
.BR %fstat
Trace fstat, fstatat, and statx syscall variants.
.TP
.BR %%stat
Trace syscalls used for requesting file status (stat, lstat, fstat, fstatat,
statx, and their variants).
.TP
.BR %statfs
Trace statfs, statfs64, statvfs, osf_statfs, and osf_statfs64 system calls.
The same effect can be achieved with
.BR "\-e\ trace" = /^(.*_)?statv?fs
regular expression.
.TP
.BR %fstatfs
Trace fstatfs, fstatfs64, fstatvfs, osf_fstatfs, and osf_fstatfs64 system calls.
The same effect can be achieved with
.BR "\-e\ trace" = /fstatv?fs
regular expression.
.TP
.BR %%statfs
Trace syscalls related to file system statistics (statfs-like, fstatfs-like,
and ustat).  The same effect can be achieved with
.BR "\-e\ trace" = /statv?fs|fsstat|ustat
regular expression.
.TP
.BR %clock
Trace system calls that read or modify system clocks.
.TP
.BR %pure
Trace syscalls that always succeed and have no arguments.
Currently, this list includes
.BR arc_gettls "(2), " getdtablesize "(2), " getegid "(2), " getegid32 "(2),"
.BR geteuid "(2), " geteuid32 "(2), " getgid "(2), " getgid32 "(2),"
.BR getpagesize "(2), " getpgrp "(2), " getpid "(2), " getppid "(2),"
.BR get_thread_area (2)
(on architectures other than x86),
.BR gettid "(2), " get_tls "(2), " getuid "(2), " getuid32 "(2),"
.BR getxgid "(2), " getxpid "(2), " getxuid "(2), " kern_features "(2), and"
.BR metag_get_tls "(2)"
syscalls.
.RE
.IP
The
.B \-c
option is useful for determining which system calls might be useful
to trace.  For example,
.BR 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
.BR trace = all .
.TP
\fB\-e\ trace\-fd\fR=\,\fIset\fR
.TQ
\fB\-e\ trace\-fds\fR=\,\fIset\fR
.TQ
\fB\-e\ fd\fR=\,\fIset\fR
.TQ
\fB\-e\ fds\fR=\,\fIset\fR
.TQ
\fB\-\-trace\-fds\fR=\,\fIset\fR
Trace only the syscalls that operate
on the specified subset of (non-negative) file descriptors.
Note that usage of this option also filters out all the syscalls
that do not operate on file descriptors at all.
Applies in (inclusive) disjunction with the \fB\-\-trace\-path\fR option.
.TP
\fB\-e\ signal\fR=\,\fIset\fR
.TQ
\fB\-e\ signals\fR=\,\fIset\fR
.TQ
\fB\-e\ s\fR=\,\fIset\fR
.TQ
\fB\-\-signal\fR=\,\fIset\fR
Trace only the specified subset of signals.  The default is
.BR signal = all .
For example,
.BR signal "=!" SIGIO
(or
.BR signal "=!" io )
causes
.B SIGIO
signals not to be traced.
.TP
\fB\-e\ status\fR=\,\fIset\fR
.TQ
\fB\-\-status\fR=\,\fIset\fR
Print only system calls with the specified return status.  The default is
.BR status = all .
When using the
.B status
qualifier, because
.B strace
waits for system calls to return before deciding whether they should be printed
or not, the traditional order of events may not be preserved anymore.  If two
system calls are executed by concurrent threads,
.B 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
.BR select (2)
is called, but a different thread calls
.BR clock_gettime (2)
before
.BR select (2)
finishes:
.CW
[pid 28779] 1130322148.939977 clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
[pid 28772] 1130322148.438139 select(4, [3], NULL, NULL, NULL) = 1 (in [3])
.CE
.I set
can include the following elements:
.RS
.TP 13
.B successful
Trace system calls that returned without an error code.
The
.B -z
option has the effect of
.BR status = successful .
.TQ
.B failed
Trace system calls that returned with an error code.
The
.B -Z
option has the effect of
.BR status = failed .
.TQ
.B unfinished
Trace system calls that did not return.  This might happen, for example, due to
an execve call in a neighbour thread.
.TQ
.B unavailable
Trace system calls that returned but strace failed to fetch the error status.
.TQ
.B detached
Trace system calls for which strace detached before the return.
.RE
.TP
.BI "\-P " path
.TQ
.BR "\-\-trace\-path" = \fIpath\fR
Trace only system calls accessing
.IR path .
Multiple
.B \-P
options can be used to specify several paths.
Applies in (inclusive) disjunction with the \fB\-\-trace\-fds\fR option.
.TP
.B \-z
.TQ
.B \-\-successful\-only
Print only syscalls that returned without an error code.
.TP
.B \-Z
.TQ
.B \-\-failed\-only
Print only syscalls that returned with an error code.
.SS Output format
.TP 12
.BI "\-a " column
.TQ
.BR "\-\-columns" = \fIcolumn\fR
Align return values in a specific column (default column 40).
.TP
\fB\-e\ abbrev\fR=\,\fIsyscall_set\fR
.TQ
\fB\-e\ a\fR=\,\fIsyscall_set\fR
.TQ
\fB\-\-abbrev\fR=\,\fIsyscall_set\fR
Abbreviate the output from printing each member of large structures.
The syntax of the
.I syscall_set
specification is the same as in the
.B "-e trace"
option.
The default is
.BR abbrev = all .
The
.B \-v
option has the effect of
.BR abbrev = none .
.TP
\fB\-e\ verbose\fR=\,\fIsyscall_set\fR
.TQ
\fB\-e\ v\fR=\,\fIsyscall_set\fR
.TQ
\fB\-\-verbose\fR=\,\fIsyscall_set\fR
Dereference structures for the specified set of system calls.
The syntax of the
.I syscall_set
specification is the same as in the
.B "-e trace"
option.
The default is
.BR verbose = all .
.TP
\fB\-e\ raw\fR=\,\fIsyscall_set\fR
.TQ
\fB\-e\ x\fR=\,\fIsyscall_set\fR
.TQ
\fB\-\-raw\fR=\,\fIsyscall_set\fR
Print raw, undecoded arguments for the specified set of system calls.
The syntax of the
.I syscall_set
specification is the same as in the
.B "-e trace"
option.
This option has the effect of causing all arguments to be printed
in hexadecimal.  This is mostly useful if you don't trust the
decoding or you need to know the actual numeric value of an
argument.
See also
.B \-X raw
option.
.TP
\fB\-e\ read\fR=\,\fIset\fR
.TQ
\fB\-e\ reads\fR=\,\fIset\fR
.TQ
\fB\-e\ r\fR=\,\fIset\fR
.TQ
\fB\-\-read\fR=\,\fIset\fR
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
.I 3
and
.I 5
use
\fB\-e\ read\fR=\,\fI3\fR,\fI5\fR.
Note that this is independent from the normal tracing of the
.BR read (2)
system call which is controlled by the option
.BR -e "\ " trace = read .
.TP
\fB\-e\ write\fR=\,\fIset\fR
.TQ
\fB\-e\ writes\fR=\,\fIset\fR
.TQ
\fB\-e\ w\fR=\,\fIset\fR
.TQ
\fB\-\-write\fR=\,\fIset\fR
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
.I 3
and
.I 5
use
\fB\-e\ write\fR=\,\fI3\fR,\,\fI5\fR.
Note that this is independent from the normal tracing of the
.BR write (2)
system call which is controlled by the option
.BR -e "\ " trace = write .
.TP
\fB\-e\ quiet\fR=\,\fIset\fR
.TQ
\fB\-e\ silent\fR=\,\fIset\fR
.TQ
\fB\-e\ silence\fR=\,\fIset\fR
.TQ
\fB\-e\ q\fR=\,\fIset\fR
.TQ
\fB\-\-quiet\fR=\,\fIset\fR
.TQ
\fB\-\-silent\fR=\,\fIset\fR
.TQ
\fB\-\-silence\fR=\,\fIset\fR
Suppress various information messages.  The default is
.BR quiet = none .
.I set
can include the following elements:
.RS
.TP 17
.B attach
Suppress messages about attaching and detaching
.RB (\[dq] "[ Process NNNN attached ]" "\[dq],"
.RB "\[dq]" "[ Process NNNN detached ]" "\[dq])."
.TQ
.B exit
Suppress messages about process exits
.RB (\[dq] "+++ exited with SSS +++" \[dq]).
.TQ
.B path-resolution
Suppress messages about resolution of paths provided via the
.B \-P
option
.RB (\[dq] "Requested path \[dq]...\[dq] resolved into \[dq]...\[dq]" \[dq]).
.TQ
.B personality
Suppress messages about process personality changes
.RB (\[dq] "[ Process PID=NNNN runs in PPP mode. ]" \[dq]).
.TQ
.B thread-execve
.TQ
.B superseded
Suppress messages about process being superseded by
.BR execve (2)
in another thread
.RB (\[dq] "+++ superseded by execve in pid NNNN +++" \[dq]).
.RE
.TP
\fB\-e\ decode\-fds\fR=\,\fIset\fR
.TQ
\fB\-\-decode\-fds\fR=\,\fIset\fR
Decode various information associated with file descriptors.  The default is
.BR decode\-fds = none .
.I set
can include the following elements:
.RS
.TP 9
.B path
Print file paths.
Also enables printing of tracee's current working directory when
.B AT_FDCWD
constant is used.
.TQ
.B socket
Print socket protocol-specific information,
.TQ
.B dev
Print character/block device numbers.
.TQ
.B pidfd
Print PIDs associated with pidfd file descriptors.
.TQ
.B signalfd
Print signal masks associated with signalfd file descriptors.
.RE
.TP
\fB\-e\ decode\-pids\fR=\,\fIset\fR
.TQ
\fB\-\-decode\-pids\fR=\,\fIset\fR
Decode various information associated with process IDs
(and also thread IDs, process group IDs, and session IDs).
The default is
.BR decode\-pids = none .
.I set
can include the following elements:
.RS
.TP 8
.B comm
Print command names associated with thread or process IDs.
.TQ
.B pidns
Print thread, process, process group, and session IDs in strace's PID namespace
if the tracee is in a different PID namespace.
.RE
.TP
.BR "\-e\ kvm" = vcpu
.TQ
.BR "\-\-kvm" = vcpu
Print the exit reason of kvm vcpu.  Requires Linux kernel version 4.16.0
or higher.
.TP
.B \-i
.TQ
.B \-\-instruction\-pointer
Print the instruction pointer at the time of the system call.
.TP
.B \-n
.TQ
.B \-\-syscall\-number
Print the syscall number.
.if '@ENABLE_STACKTRACE_FALSE@'#' .TP
.if '@ENABLE_STACKTRACE_FALSE@'#' .B \-k
.if '@ENABLE_STACKTRACE_FALSE@'#' .TQ
.if '@ENABLE_STACKTRACE_FALSE@'#' .B \-\-stack\-traces
.if '@ENABLE_STACKTRACE_FALSE@'#' Print the execution stack trace of the traced
.if '@ENABLE_STACKTRACE_FALSE@'#' processes after each system call.
.TP
.BI "\-o " filename
.TQ
.BR "\-\-output" = \fIfilename\fR
Write the trace output to the file
.I filename
rather than to stderr.
.IR filename . pid
form is used if
.B \-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
.B \-ff
option currently.
.TP
.B \-A
.TQ
.B \-\-output\-append\-mode
Open the file provided in the
.B \-o
option in append mode.
.TP
.B \-q
.TQ
.B \-\-quiet
.TQ
.BR \-\-quiet = attach , personality
Suppress 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.
.TP
.B \-qq
.TQ
.BR \-\-quiet = attach , personality , exit
Suppress messages attaching, detaching, personality changes,
and about process exit status.
.TP
.B \-qqq
.TQ
.BR \-\-quiet = all
Suppress all suppressible messages (please refer to the
.B -e quiet
option description for the full list of suppressible messages).
.TP
.B \-r
.TQ
.BR \-\-relative\-timestamps [= \fIprecision\fR ]
Print a relative timestamp upon entry to each system call.  This
records the time difference between the beginning of successive
system calls.
.I precision
can be one of
.BR s " (for seconds), " ms " (milliseconds), " us " (microseconds), or " ns
(nanoseconds), and allows setting the precision of time value being printed.
Default is
.B us
(microseconds).
Note that since
.B \-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
.B \-t
option.
.TP
.BI "\-s " strsize
.TQ
.BR "\-\-string\-limit" = \fIstrsize\fR
Specify the maximum string size to print (the default is 32).  Note
that filenames are not considered strings and are always printed in
full.
.TP
.BR \-\-absolute\-timestamps [=[[ format: ] \fIformat\fR ],[[ precision: ] \fIprecision ]]
.TQ
.BR \-\-timestamps [=[[ format: ] \fIformat\fR ],[[ precision: ] \fIprecision ]]
Prefix each line of the trace with the wall clock time in the specified
.I format
with the specified
.IR precision .
.I format
can be one of the following:
.RS
.TP 14
.B none
No time stamp is printed.
Can be used to override the previous setting.
.TQ
.B time
Wall clock time
.RB ( strftime (3)
format string is
.BR %T ).
.TQ
.B unix
Number of seconds since the epoch
.RB ( strftime (3)
format string is
.BR %s ).
.RE
.IP
.I precision
can be one of
.BR s " (for seconds), " ms " (milliseconds), " us " (microseconds), or " ns
(nanoseconds).
Default arguments for the option are
.BR format:time , precision:s .
.TP
.B \-t
.TQ
.B \-\-absolute\-timestamps
Prefix each line of the trace with the wall clock time.
.TP
.B \-tt
.TQ
.BR \-\-absolute\-timestamps = precision:us
If given twice, the time printed will include the microseconds.
.TP
.B \-ttt
.TQ
.BR \-\-absolute\-timestamps = format:unix , precision:us
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.
.TP
.B \-T
.TQ
.BR \-\-syscall\-times [= \fIprecision\fR ]
Show the time spent in system calls.  This records the time
difference between the beginning and the end of each system call.
.I precision
can be one of
.BR s " (for seconds), " ms " (milliseconds), " us " (microseconds), or " ns
(nanoseconds), and allows setting the precision of time value being printed.
Default is
.B us
(microseconds).
.TP
.B \-v
.TQ
.B \-\-no\-abbrev
Print unabbreviated versions of environment, stat, termios, etc.
calls.  These structures are very common in calls and so the default
behavior displays a reasonable subset of structure members.  Use
this option to get all of the gory details.
.TP
.BR \-\-strings\-in\-hex [= \fIoption\fR ]
Control usage of escape sequences with hexadecimal numbers
in the printed strings.
Normally (when no
.BR \-\-strings\-in\-hex " or " \-x
option is supplied),
escape sequences are used to print non-printable and non-ASCII characters
(that is, characters with a character code less than 32 or greater than 127),
or to disambiguate the output
(so, for quotes and other characters that encase the printed string,
for example, angle brackets, in case of file descriptor path output);
for the former use case, unless it is a white space character
that has a symbolic escape sequence defined in the C standard
(that is, \(lq\fB\\t\fR\(rq for a horizontal tab,
\(lq\fB\\n\fR\(rq for a newline,
\(lq\fB\\v\fR\(rq for a vertical tab,
\(lq\fB\\f\fR\(rq for a form feed page break,
and \(lq\fB\\r\fR\(rq for a carriage return)
are printed using escape sequences with numbers that correspond
to their byte values, with octal number format being the default.
.I option
can be one of the following:
.RS
.TP 17
.B 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.
.TQ
.B non-ascii-chars
Hexadecimal numbers are used instead of octal in the escape sequences.
.TQ
.B non-ascii
Strings that contain non-ASCII characters are printed using escape sequences
with hexadecimal numbers.
.TQ
.B all
All strings are printed using escape sequences with hexadecimal numbers.
.RE
.IP
When the option is supplied without an argument,
.B all
is assumed.
.TP
.B \-x
.TQ
.BR \-\-strings\-in\-hex = non\-ascii
Print all non-ASCII strings in hexadecimal string format.
.TP
.B \-xx
.TQ
.BR \-\-strings\-in\-hex [= all ]
Print all strings in hexadecimal string format.
.TP
.BI "\-X " format
.TQ
.BR "\-\-const\-print\-style" = \fIformat\fR
Set the format for printing of named constants and flags.
Supported
.I format
values are:
.RS
.TP 10
.B raw
Raw number output, without decoding.
.TQ
.B abbrev
Output a named constant or a set of flags instead of the raw number if they are
found.
This is the default
.B strace
behaviour.
.TQ
.B verbose
Output both the raw value and the decoded string (as a comment).
.RE
.TP
.B \-y
.TQ
.B \-\-decode\-fds
.TQ
.BR \-\-decode\-fds = path
Print paths associated with file descriptor arguments and with the
.B AT_FDCWD
constant.
.TP
.B \-yy
.TQ
.BR \-\-decode\-fds = all
Print 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.
.TP
.B \-\-pidns\-translation
.TQ
.BR \-\-decode\-pids = pidns
If strace and tracee are in different PID namespaces, print PIDs in
strace's namespace, too.
.TP
.B \-Y
.TQ
.BR \-\-decode\-pids = comm
Print command names for PIDs.
.if '@ENABLE_SECONTEXT_FALSE@'#' .TP
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR \-\-secontext\fR[=\fIformat\fR]
.if '@ENABLE_SECONTEXT_FALSE@'#' .TQ
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR \-e\ secontext\fR=\fIformat\fR
.if '@ENABLE_SECONTEXT_FALSE@'#' When SELinux is available and is not disabled,
.if '@ENABLE_SECONTEXT_FALSE@'#' print in square brackets SELinux contexts of
.if '@ENABLE_SECONTEXT_FALSE@'#' processes, files, and descriptors.  The
.if '@ENABLE_SECONTEXT_FALSE@'#' .I format
.if '@ENABLE_SECONTEXT_FALSE@'#' argument is a comma-separated list of items
.if '@ENABLE_SECONTEXT_FALSE@'#' being one of the following:
.if '@ENABLE_SECONTEXT_FALSE@'#' .RS
.if '@ENABLE_SECONTEXT_FALSE@'#' .TP 18
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR full
.if '@ENABLE_SECONTEXT_FALSE@'#' Print the full context (user, role, type level
.if '@ENABLE_SECONTEXT_FALSE@'#' and category).
.if '@ENABLE_SECONTEXT_FALSE@'#' .TQ
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR mismatch
.if '@ENABLE_SECONTEXT_FALSE@'#' Also print the context recorded by the SELinux
.if '@ENABLE_SECONTEXT_FALSE@'#' database in case the current context differs.
.if '@ENABLE_SECONTEXT_FALSE@'#' The latter is printed after two exclamation marks (!!).
.if '@ENABLE_SECONTEXT_FALSE@'#' .RE
.if '@ENABLE_SECONTEXT_FALSE@'#' .IP
.if '@ENABLE_SECONTEXT_FALSE@'#' The default value for
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR \-\-secontext
.if '@ENABLE_SECONTEXT_FALSE@'#' is
.if '@ENABLE_SECONTEXT_FALSE@'#' .BR !full,mismatch
.if '@ENABLE_SECONTEXT_FALSE@'#' which prints only the type instead of full context
.if '@ENABLE_SECONTEXT_FALSE@'#' and doesn't check for context mismatches.
.SS Statistics
.TP 12
.B \-c
.TQ
.B \-\-summary\-only
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
.B \-c
is used with
.BR \-f ,
only aggregate totals for all traced processes are kept.
.TP
.B \-C
.TQ
.B \-\-summary
Like
.B \-c
but also print regular output while processes are running.
.TP
.BI "\-O " overhead
.TQ
.BR "\-\-summary\-syscall\-overhead" = \fIoverhead\fR
Set the overhead for tracing system calls to
.IR overhead .
This is useful for overriding the default heuristic for guessing
how much time is spent in mere measuring when timing system calls using
the
.B \-c
option.  The accuracy of the heuristic can be gauged by timing a given
program run without tracing (using
.BR time (1))
and comparing the accumulated
system call time to the total produced using
.BR \-c .
.IP
The format of
.I overhead
specification is described in section
.IR "Time specification format description".
.TP
.BI "\-S " sortby
.TQ
.BR "\-\-summary\-sort\-by" = \fIsortby\fR
Sort the output of the histogram printed by the
.B \-c
option by the specified criterion.  Legal values are
.BR time " (or " time\-percent " or " time\-total " or " total\-time ),
.BR min\-time " (or " shortest " or " time\-min ),
.BR max\-time " (or " longest " or " time\-max ),
.BR avg\-time " (or " time\-avg ),
.BR calls " (or " count ),
.BR errors " (or " error ),
.BR name " (or " syscall " or " syscall\-name ),
and
.BR nothing " (or " none );
default is
.BR time .
.TP
.BI "\-U " columns
.TQ
.BR "\-\-summary\-columns" = \fIcolumns\fR
Configure a set (and order) of columns being shown in the call summary.
The
.I columns
argument is a comma-separated list with items being one of the following:
.RS
.TP 36
.BR time\-percent " (or " time )
Percentage of cumulative time consumed by a specific system call.
.TQ
.BR total\-time " (or " time\-total )
Total system (or wall clock, if
.B \-w
option is provided) time consumed by a specific system call.
.TQ
.BR min\-time " (or " shortest " or " time\-min )
Minimum observed call duration.
.TQ
.BR max\-time " (or " longest " or " time\-max )
Maximum observed call duration.
.TQ
.BR avg\-time " (or " time\-avg )
Average call duration.
.TQ
.BR calls " (or " count )
Call count.
.TQ
.BR errors " (or " error )
Error count.
.TQ
.BR name " (or " syscall " or " syscall\-name )
Syscall name.
.RE
.IP
The default value is
.BR time\-percent , total\-time , avg\-time , calls , errors , name .
If the
.B name
field is not supplied explicitly, it is added as the last column.
.TP
.B \-w
.TQ
.B \-\-summary\-wall\-clock
Summarise the time difference between the beginning and end of
each system call.  The default is to summarise the system time.
.SS Tampering
.ad l
.TP 12
\fB\-e\ inject\fR=\,\fIsyscall_set\/\fR[:\fBerror\fR=\,\fIerrno\/\fR|:\fBretval\fR=\,\fIvalue\/\fR]\:[:\fBsignal\fR=\,\fIsig\/\fR]\:[:\fBsyscall\fR=\,\fIsyscall\/\fR]\:[:\fBdelay_enter\fR=\,\fIdelay\/\fR]\:[:\fBdelay_exit\fR=\,\fIdelay\/\fR]\:[:\fBpoke_enter\fR=\,\fI@argN=DATAN,@argM=DATAM...\/\fR]\:[:\fBpoke_exit\fR=\,\fI@argN=DATAN,@argM=DATAM...\/\fR]\:[:\fBwhen\fR=\,\fIexpr\/\fR] \{
.TQ
\fB\-\-inject\fR=\,\fIsyscall_set\/\fR[:\fBerror\fR=\,\fIerrno\/\fR|:\fBretval\fR=\,\fIvalue\/\fR]\:[:\fBsignal\fR=\,\fIsig\/\fR]\:[:\fBsyscall\fR=\,\fIsyscall\/\fR]\:[:\fBdelay_enter\fR=\,\fIdelay\/\fR]\:[:\fBdelay_exit\fR=\,\fIdelay\/\fR]\:[:\fBpoke_enter\fR=\,\fI@argN=DATAN,@argM=DATAM...\/\fR]\:[:\fBpoke_exit\fR=\,\fI@argN=DATAN,@argM=DATAM...\/\fR]\:[:\fBwhen\fR=\,\fIexpr\/\fR] \{
.ad b
Perform syscall tampering for the specified set of syscalls.
The syntax of the
.I syscall_set
specification is the same as in the
.B "-e trace"
option.
.IP
At least one of
.BR error ,
.BR retval ,
.BR signal ,
.BR delay_enter ,
.BR delay_exit ,
.BR poke_enter ,
or
.B poke_exit
options has to be specified.
.B error
and
.B retval
are mutually exclusive.
.IP
If :\fBerror\fR=\,\fIerrno\/\fR 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 :\fBsyscall=\fR option),
and the error code is specified using a symbolic
.I errno
value like
.B ENOSYS
or a numeric value within 1..4095 range.
.IP
If :\fBretval\fR=\,\fIvalue\/\fR option is specified,
success injection is performed: the syscall number is replaced by -1,
but a bogus success value is returned to the callee.
.IP
If :\fBsignal\fR=\,\fIsig\/\fR option is specified with either a symbolic value
like
.B SIGSEGV
or a numeric value within 1..\fBSIGRTMAX\fR range,
that signal is delivered on entering every syscall specified by the
.IR set .
.IP
If :\fBdelay_enter\fR=\,\fIdelay\/\fR or :\fBdelay_exit\fR=\,\fIdelay\/\fR
options are specified, delay injection is performed: the tracee is delayed
by time period specified by
.IR delay
on entering or exiting the syscall, respectively.
The format of
.I delay
specification is described in section
.IR "Time specification format description".
.IP
If :\fBpoke_enter\fR=\fI@argN=DATAN,@argM=DATAM...\fR
or :\fBpoke_exit\fR=\fI@argN=DATAN,@argM=DATAM...\fR options are specified,
tracee's memory at locations, pointed to by system call arguments
.IR argN
and
.IR argM
(going from
.IR arg1
to
.IR arg7 )
is overwritten by data
.IR DATAN
and
.IR DATAM
(specified in hexadecimal format; for example :\fBpoke_enter\fR=\fI@arg1=0000DEAD0000BEEF\fR).
:\fBpoke_enter\fR modifies memory on syscall enter, and :\fBpoke_exit\fR - on exit.
.IP
If :\fBsignal\fR=\,\fIsig\/\fR option is specified without
:\fBerror\fR=\,\fIerrno\/\fR, :\fBretval\fR=\,\fIvalue\/\fR or
:\fBdelay_{enter,exit}\fR=\,\fIusecs\/\fR options,
then only a signal
.I sig
is delivered without a syscall fault or delay injection.
Conversely, :\fBerror\fR=\,\fIerrno\/\fR or
:\fBretval\fR=\,\fIvalue\/\fR option without
:\fBdelay_enter\fR=\,\fIdelay\/\fR,
:\fBdelay_exit\fR=\,\fIdelay\/\fR or
:\fBsignal\fR=\,\fIsig\/\fR options injects a fault without delivering a signal
or injecting a delay, etc.
.IP
If
:\fBsignal\fR=\,\fIsig\/\fR
option is specified together with
:\fBerror\fR=\,\fIerrno\/\fR or :\fBretval\fR=\,\fIvalue\/\fR,
then both injection of a fault or success and signal delivery are performed.
.IP
if :\fBsyscall\fR=\fIsyscall\fR option is specified, the corresponding syscall
with no side effects is injected instead of -1.
Currently, only "pure" (see
.BR "-e trace" = "%pure"
description) syscalls can be specified there.
.IP
Unless a :\fBwhen\fR=\,\fIexpr\fR subexpression is specified,
an injection is being made into every invocation of each syscall from the
.IR set .
.IP
The format of the subexpression is:
.RS 15
.IP
\fIfirst\/\fR[\fB..\fR\,\fIlast\/\fR][\fB+\fR[\,\fIstep\/\fR]]
.RE
.IP
Number
.I first
stands for the first invocation number in the range, number
.I last
stands for the last invocation number in the range, and
.I step
stands for the step between two consecutive invocations.
The following combinations are useful:
.RS
.TP 18
.I first
For every syscall from the
.IR set ,
perform an injection for the syscall invocation number
.I first
only.
.TQ
\fIfirst\/\fB..\fR\,\fIlast\fR
For every syscall from the
.IR set ,
perform an injection for the syscall invocation number
.I first
and all subsequent invocations until the invocation number
.I last
(inclusive).
.TQ
\fIfirst\/\fB+\fR
For every syscall from the
.IR set ,
perform injections for the syscall invocation number
.I first
and all subsequent invocations.
.TQ
\fIfirst\/\fB..\fR\,\fIlast\/\fB+\fR
For every syscall from the
.IR set ,
perform injections for the syscall invocation number
.I first
and all subsequent invocations until the invocation number
.I last
(inclusive).
.TQ
\fIfirst\/\fB+\fR\,\fIstep\fR
For every syscall from the
.IR set ,
perform injections for syscall invocations number
.IR first ,
.IR first + step ,
.IR first + step + step ,
and so on.
.TQ
\fIfirst\/\fB..\fR\,\fIlast\fB+\fR\,\fIstep\fR
Same as the previous, but consider only syscall invocations with numbers up to
.I last
(inclusive).
.RE
.IP
For example, to fail each third and subsequent chdir syscalls with
.BR ENOENT ,
use
\fB\-e\ inject\fR=\,\fIchdir\/\fR:\fBerror\fR=\,\fIENOENT\/\fR:\fBwhen\fR=\,\fI3\/\fB+\fR.
.IP
The valid range for numbers
.I first
and
.I step
is 1..65535, and for number
.I last
is 1..65534.
.IP
An injection expression can contain only one
.BR error =
or
.BR retval =
specification, and only one
.BR signal =
specification.  If an injection expression contains multiple
.BR when =
specifications, the last one takes precedence.
.IP
Accounting of syscalls that are subject to injection
is done per syscall and per tracee.
.IP
Specification of syscall injection can be combined
with other syscall filtering options, for example,
\fB\-P \fI/dev/urandom \fB\-e inject\fR=\,\fIfile\/\fR:\fBerror\fR=\,\fIENOENT\fR.
.TP
\fB\-e\ fault\fR=\,\fIsyscall_set\/\fR[:\fBerror\fR=\,\fIerrno\/\fR][:\fBwhen\fR=\,\fIexpr\/\fR]
.TQ
\fB\-\-fault\fR=\,\fIsyscall_set\/\fR[:\fBerror\fR=\,\fIerrno\/\fR][:\fBwhen\fR=\,\fIexpr\/\fR]
Perform syscall fault injection for the specified set of syscalls.
.IP
This is equivalent to more generic
\fB\-e\ inject\fR= expression with default value of
.I errno
option set to
.BR ENOSYS .
.SS Miscellaneous
.TP 12
.B \-d
.TQ
.B \-\-debug
Show some debugging output of
.B strace
itself on the standard error.
.TP
.B \-F
This option is deprecated.  It is retained for backward compatibility only
and may be removed in future releases.
Usage of multiple instances of
.B \-F
option is still equivalent to a single
.BR \-f ,
and it is ignored at all if used along with one or more instances of
.B \-f
option.
.TP
.B \-h
.TQ
.B \-\-help
Print the help summary.
.TP
.B \-\-seccomp\-bpf
Try to enable use of seccomp-bpf (see
.BR seccomp (2))
to have
.BR ptrace (2)-stops
only when system calls that are being traced occur in the traced processes.
This option has no effect unless
.BR \-f / \-\-follow\-forks
is also specified.
.B \-\-seccomp\-bpf
is also not applicable to processes attached using
.BR \-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
.B strace
itself is being traced.
In cases when seccomp-bpf filter setup failed,
.B strace
proceeds as usual and stops traced processes on every system call.
.TP
.BR \-\-tips [=[[ id: ] \fIid\fR ],[[ format: ] \fIformat\fR ]]
Show strace tips, tricks, and tweaks before exit.
.I id
can be a non-negative integer number,
which enables printing of specific tip, trick, or tweak
(these ID are not guaranteed to be stable),
or
.B random
(the default),
in which case a random tip is printed.
.I format
can be one of the following:
.RS
.TP 9
.B none
No tip is printed.
Can be used to override the previous setting.
.TQ
.B compact
Print the tip just big enough to contain all the text.
.TQ
.B full
Print the tip in its full glory.
.RE
.IP
Default is
.BR id:random,format:compact .
.TP
.B \-V
.TQ
.B \-\-version
Print the version number of
.BR strace .
Multiple instances of the option beyond specific threshold tend to increase
Strauss awareness.
.SS "Time specification format description"
.PP
Time values can be specified as a decimal floating point number
(in a format accepted by
.BR strtod (3)),
optionally followed by one of the following suffices that specify
the unit of time:
.B s
(seconds),
.B ms
(milliseconds),
.B us
(microseconds), or
.B ns
(nanoseconds).
If no suffix is specified, the value is interpreted as microseconds.
.PP
The described format is used for
.BR \-O ", " "\-e inject" = delay_enter ", and " "\-e inject" = delay_exit
options.
.SH DIAGNOSTICS
When
.I command
exits,
.B strace
exits with the same exit status.
If
.I command
is terminated by a signal,
.B strace
terminates itself with the same signal, so that
.B strace
can be used as a wrapper process transparent to the invoking parent process.
Note that parent-child relationship (signal stop notifications,
.BR getppid (2)
value, etc) between traced process and its parent are not preserved
unless
.B \-D
is used.
.LP
When using
.B \-p
without a
.IR command ,
the exit status of
.B strace
is zero unless no processes has been attached or there was an unexpected error
in doing the tracing.
.SH "SETUID INSTALLATION"
If
.B 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
.B 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
.B strace
with mode 'rwsr-xr--', user
.B root
and group
.BR trace ,
where members of the
.B trace
group are trusted users.
If you do use this feature, please remember to install
a regular non-setuid version of
.B strace
for ordinary users to use.
.SH "MULTIPLE PERSONALITIES SUPPORT"
On some architectures,
.B strace
supports decoding of syscalls for processes that use different ABI rather than
the one
.B strace
uses.
Specifically, in addition to decoding native ABI,
.B strace
can decode the following ABIs on the following architectures:
.TS H
allbox;
lb lb
l l.
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
.TE
.RS 0
.TP 5
[1]
When
.B strace
is built as an x86_64 application
.TQ
[2]
When
.B strace
is built as an x32 application
.TQ
[3]
Big endian only
.RE
.PP
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
.B strace \-V
command in order to figure out what support is available in your
.B strace
build ("non-native" refers to an ABI that differs from the ABI
.B strace
has):
.TP 15
.B m32-mpers
.B strace
can trace and properly decode non-native 32-bit binaries.
.TQ
.B no-m32-mpers
.B strace
can trace, but cannot properly decode non-native 32-bit binaries.
.TQ
.B mx32-mpers
.B strace
can trace and properly decode non-native 32-on-64-bit binaries.
.TQ
.B no-mx32-mpers
.B strace
can trace, but cannot properly decode non-native 32-on-64-bit binaries.
.PP
If the output contains neither
.B m32-mpers
nor
.BR no-m32-mpers ,
then decoding of non-native 32-bit binaries is not implemented at all
or not applicable.
.PP
Likewise, if the output contains neither
.B mx32-mpers
nor
.BR no-mx32-mpers ,
then decoding of non-native 32-on-64-bit binaries is not implemented at all
or not applicable.
.SH NOTES
It is a pity that so much tracing clutter is produced by systems
employing shared libraries.
.LP
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.
.LP
In some cases, a system call will differ from the documented behavior
or have a different name.  For example, the
.BR faccessat (2)
system call does not have
.I flags
argument, and the
.BR setrlimit (2)
library function uses
.BR 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.
.LP
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
.BR __NR_ *
kernel macros of the tracee's architecture and personality.
There are two exceptions from this general rule:
.BR arm_fadvise64_64 (2)
ARM syscall and
.BR xtensa_fadvise64_64 (2)
Xtensa syscall are filtered and printed as
.BR fadvise64_64 (2).
.LP
On x32, syscalls that are intended to be used by 64-bit processes and not x32
ones (for example,
.BR readv (2),
that has syscall number 19 on x86_64, with its x32 counterpart has syscall
number 515), but called with
.B __X32_SYSCALL_BIT
flag being set, are designated with
.B "#64"
suffix.
.LP
On some platforms a process that is attached to with the
.B \-p
option may observe a spurious
.B EINTR
return from the current system call that is not restartable.
(Ideally, all system calls should be restarted on
.B 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.
.LP
As
.B strace
executes the specified
.I 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
.B ENOEXEC
error.
It is advisable to manually supply a shell as a
.I command
with the script as its argument.
.SH BUGS
Programs that use the
.I setuid
bit do not have
effective user
.SM ID
privileges while being traced.
.LP
A traced process runs slowly (but check out the
.B \-\-seccomp\-bpf
option).
.LP
Traced processes which are descended from
.I command
may be left running after an interrupt signal
.RB ( CTRL\-C ).
.SH HISTORY
The original
.B strace
was written by Paul Kranenburg
for SunOS and was inspired by its
.B trace
utility.
The SunOS version of
.B strace
was ported to Linux and enhanced
by Branko Lankester, who also wrote the Linux kernel support.
Even though Paul released
.B strace
2.5 in 1992,
Branko's work was based on Paul's
.B strace
1.5 release from 1991.
In 1993, Rick Sladkey merged
.B strace
2.5 for SunOS and the second release of
.B strace
for Linux, added many of the features of
.BR truss (1)
from SVR4, and produced an
.B strace
that worked on both platforms.  In 1994 Rick ported
.B strace
to SVR4 and Solaris and wrote the
automatic configuration support.  In 1995 he ported
.B strace
to Irix
and became tired of writing about himself in the third person.
.PP
Beginning with 1996,
.B strace
was maintained by Wichert Akkerman.
During his tenure,
.B 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
.B strace
maintainership was transferred to Roland McGrath.
Since then,
.B 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;
.B strace
development migrated to
.B Git
during that period.
Since 2009,
.B strace
is actively maintained by Dmitry Levin.
.B strace
gained support for AArch64, ARC, AVR32, Blackfin, Meta, Nios II, OpenRISC 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
.B 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.
.PP
For the additional information, please refer to the
.B NEWS
file and
.B strace
repository commit log.
.SH REPORTING BUGS
Problems with
.B strace
should be reported to the
.UR mailto:strace\-devel@lists.strace.io
.B strace
mailing list
.UE .
.SH "SEE ALSO"
.BR strace-log-merge (1),
.BR ltrace (1),
.BR perf-trace (1),
.BR trace-cmd (1),
.BR time (1),
.BR ptrace (2),
.BR syscall (2),
.BR proc (5),
.BR signal (7)
.PP
.UR https://strace.io/
.B strace
Home Page
.UE
.SH AUTHORS
The complete list of
.B strace
contributors can be found in the
.B CREDITS
file.