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STRACE(1) General Commands Manual STRACE(1)
strace - trace system calls and signals
strace [-ACdffhikqqrtttTvVwxxyyzZ] [-I n] [-b execve] [-e expr]...
[-O overhead] [-S sortby] [-U columns] [-a column] [-o file]
[-s strsize] [-X format] [-P path]... [-p pid]...
[--seccomp-bpf] { -p pid | [-DDD] [-E var[=val]]...
[-u username] command [args] }
strace -c [-dfwzZ] [-I n] [-b execve] [-e expr]... [-O overhead]
[-S sortby] [-U columns] [-P path]... [-p pid]...
[--seccomp-bpf] { -p pid | [-DDD] [-E var[=val]]...
[-u username] command [args] }
In the simplest case strace runs the specified command until it
exits. It intercepts and records the system calls which are called
by a process and the signals which are received by a process. The
name of each system call, its arguments and its return value are
printed on standard error or to the file specified with the -o
option.
strace is a useful diagnostic, instructional, and debugging tool.
System administrators, diagnosticians and trouble-shooters will find
it invaluable for solving problems with programs for which the source
is not readily available since they do not need to be recompiled in
order to trace them. Students, hackers and the overly-curious will
find that a great deal can be learned about a system and its system
calls by tracing even ordinary programs. And programmers will find
that since system calls and signals are events that happen at the
user/kernel interface, a close examination of this boundary is very
useful for bug isolation, sanity checking and attempting to capture
race conditions.
Each line in the trace contains the system call name, followed by its
arguments in parentheses and its return value. An example from
stracing the command "cat /dev/null" is:
open("/dev/null", O_RDONLY) = 3
Errors (typically a return value of -1) have the errno symbol and
error string appended.
open("/foo/bar", O_RDONLY) = -1 ENOENT (No such file or directory)
Signals are printed as signal symbol and decoded siginfo structure.
An excerpt from stracing and interrupting the command "sleep 666" is:
sigsuspend([] <unfinished ...>
--- SIGINT {si_signo=SIGINT, si_code=SI_USER, si_pid=...} ---
+++ killed by SIGINT +++
If a system call is being executed and meanwhile another one is being
called from a different thread/process then strace will try to
preserve the order of those events and mark the ongoing call as being
unfinished. When the call returns it will be marked as resumed.
[pid 28772] select(4, [3], NULL, NULL, NULL <unfinished ...>
[pid 28779] clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
[pid 28772] <... select resumed> ) = 1 (in [3])
Interruption of a (restartable) system call by a signal delivery is
processed differently as kernel terminates the system call and also
arranges its immediate reexecution after the signal handler
completes.
read(0, 0x7ffff72cf5cf, 1) = ? ERESTARTSYS (To be restarted)
--- SIGALRM ... ---
rt_sigreturn(0xe) = 0
read(0, "", 1) = 0
Arguments are printed in symbolic form with passion. This example
shows the shell performing ">>xyzzy" output redirection:
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
Here, the second and the third argument of 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, strace output is proven
to be more readable than the source.
Structure pointers are dereferenced and the members are displayed as
appropriate. In most cases, arguments are formatted in the most C-
like fashion possible. For example, the essence of the command "ls
-l /dev/null" is captured as:
lstat("/dev/null", {st_mode=S_IFCHR|0666, st_rdev=makedev(0x1, 0x3), ...}) = 0
Notice how the 'struct stat' argument is dereferenced and how each
member is displayed symbolically. In particular, observe how the
st_mode member is carefully decoded into a bitwise-OR of symbolic and
numeric values. Also notice in this example that the first argument
to lstat(2) is an input to the system call and the second argument is
an output. Since output arguments are not modified if the system
call fails, arguments may not always be dereferenced. For example,
retrying the "ls -l" example with a non-existent file produces the
following line:
lstat("/foo/bar", 0xb004) = -1 ENOENT (No such file or directory)
In this case the porch light is on but nobody is home.
Syscalls unknown to strace are printed raw, with the unknown system
call number printed in hexadecimal form and prefixed with "syscall_":
syscall_0xbad(0x1, 0x2, 0x3, 0x4, 0x5, 0x6) = -1 ENOSYS (Function not implemented)
Character pointers are dereferenced and printed as C strings. Non-
printing characters in strings are normally represented by ordinary C
escape codes. Only the first strsize (32 by default) bytes of
strings are printed; longer strings have an ellipsis appended
following the closing quote. Here is a line from "ls -l" where the
getpwuid(3) library routine is reading the password file:
read(3, "root::0:0:System Administrator:/"..., 1024) = 422
While structures are annotated using curly braces, simple pointers
and arrays are printed using square brackets with commas separating
elements. Here is an example from the command id(1) on a system with
supplementary group ids:
getgroups(32, [100, 0]) = 2
On the other hand, bit-sets are also shown using square brackets, but
set elements are separated only by a space. Here is the shell,
preparing to execute an external command:
sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0
Here, the second argument is a bit-set of two signals, SIGCHLD and
SIGTTOU. In some cases, the bit-set is so full that printing out the
unset elements is more valuable. In that case, the bit-set is
prefixed by a tilde like this:
sigprocmask(SIG_UNBLOCK, ~[], NULL) = 0
Here, the second argument represents the full set of all signals.
General
-e expr A qualifying expression which modifies which events to
trace or how to trace them. The format of the expression
is:
[qualifier=][!]value[,value]...
where qualifier is one of trace (or t), 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),
decode-fds (or decode-fd), or kvm, and value is a
qualifier-dependent symbol or number. The default
qualifier is trace. Using an exclamation mark negates
the set of values. For example, -e open means literally
-e trace=open which in turn means trace only the open
system call. By contrast, -e trace=!open means to trace
every system call except open. In addition, the special
values all and none have the obvious meanings.
Note that some shells use the exclamation point for
history expansion even inside quoted arguments. If so,
you must escape the exclamation point with a backslash.
Startup
-E var=val
--env=var=val
Run command with var=val in its list of environment
variables.
-E var
--env=var Remove var from the inherited list of environment
variables before passing it on to the command.
-p pid
--attach=pid
Attach to the process with the process ID pid and begin
tracing. The trace may be terminated at any time by a
keyboard interrupt signal (CTRL-C). strace will respond
by detaching itself from the traced process(es) leaving
it (them) to continue running. Multiple -p options can
be used to attach to many processes in addition to
command (which is optional if at least one -p option is
given). -p "`pidof PROG`" syntax is supported.
-u username
--user=username
Run command with the user ID, group ID, and supplementary
groups of username. This option is only useful when
running as root and enables the correct execution of
setuid and/or setgid binaries. Unless this option is
used setuid and setgid programs are executed without
effective privileges.
Tracing
-b syscall
--detach-on=syscall
If specified syscall is reached, detach from traced
process. Currently, only execve(2) syscall is supported.
This option is useful if you want to trace multi-threaded
process and therefore require -f, but don't want to trace
its (potentially very complex) children.
-D
--daemonize
--daemonize=grandchild
Run tracer process as a grandchild, not as the parent of
the tracee. This reduces the visible effect of strace by
keeping the tracee a direct child of the calling process.
-DD
--daemonize=pgroup
--daemonize=pgrp
Run tracer process as tracee's grandchild in a separate
process group. In addition to reduction of the visible
effect of strace, it also avoids killing of strace with
kill(2) issued to the whole process group.
-DDD
--daemonize=session
Run tracer process as tracee's grandchild in a separate
session ("true daemonisation"). In addition to reduction
of the visible effect of strace, it also avoids killing
of strace upon session termination.
-f
--follow-forks
Trace child processes as they are created by currently
traced processes as a result of the fork(2), vfork(2) and
clone(2) system calls. Note that -p PID -f will attach
all threads of process PID if it is multi-threaded, not
only thread with thread_id = PID.
--output-separately
If the --output=filename option is in effect, each
processes trace is written to filename.pid where pid is
the numeric process id of each process.
-ff
--follow-forks --output-separately
Combine the effects of --follow-forks and
--output-separately options. This is incompatible with
-c, since no per-process counts are kept.
One might want to consider using strace-log-merge(1) to
obtain a combined strace log view.
-I interruptible
--interruptible=interruptible
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
syscall (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).
Filtering
-e trace=syscall_set
--trace=syscall_set
Trace only the specified set of system calls.
syscall_set is defined as [!]value[,value], and value can
be one of the following:
syscall Trace specific syscall, specified by its
name (but see NOTES).
?value Question mark before the syscall
qualification allows suppression of error in
case no syscalls matched the qualification
provided.
/regex Trace only those system calls that match the
regex. You can use POSIX Extended Regular
Expression syntax (see regex(7)).
syscall@64 Trace syscall only for the 64-bit
personality.
syscall@32 Trace syscall only for the 32-bit
personality.
syscall@x32 Trace syscall only for the 32-on-64-bit
personality.
%file
file Trace all system calls which take a file
name as an argument. You can think of this
as an abbreviation for
-e trace=open,stat,chmod,unlink,... which
is useful to seeing what files the process
is referencing. Furthermore, using the
abbreviation will ensure that you don't
accidentally forget to include a call like
lstat(2) in the list. Betchya woulda forgot
that one. The syntax without a preceding
percent sign ("-e trace=file") is
deprecated.
%process
process Trace system calls associated with process
lifecycle (creation, exec, termination).
The syntax without a preceding percent sign
("-e trace=process") is deprecated.
%net
%network
network Trace all the network related system calls.
The syntax without a preceding percent sign
("-e trace=network") is deprecated.
%signal
signal Trace all signal related system calls. The
syntax without a preceding percent sign ("-e
trace=signal") is deprecated.
%ipc
ipc Trace all IPC related system calls. The
syntax without a preceding percent sign ("-e
trace=ipc") is deprecated.
%desc
desc Trace all file descriptor related system
calls. The syntax without a preceding
percent sign ("-e trace=desc") is
deprecated.
%memory
memory Trace all memory mapping related system
calls. The syntax without a preceding
percent sign ("-e trace=memory") is
deprecated.
%creds Trace system calls that read or modify user
and group identifiers or capability sets.
%stat Trace stat syscall variants.
%lstat Trace lstat syscall variants.
%fstat Trace fstat, fstatat, and statx syscall
variants.
%%stat Trace syscalls used for requesting file
status (stat, lstat, fstat, fstatat, statx,
and their variants).
%statfs Trace statfs, statfs64, statvfs, osf_statfs,
and osf_statfs64 system calls. The same
effect can be achieved with
-e trace=/^(.*_)?statv?fs regular
expression.
%fstatfs Trace fstatfs, fstatfs64, fstatvfs,
osf_fstatfs, and osf_fstatfs64 system calls.
The same effect can be achieved with
-e trace=/fstatv?fs regular expression.
%%statfs Trace syscalls related to file system
statistics (statfs-like, fstatfs-like, and
ustat). The same effect can be achieved
with -e trace=/statv?fs|fsstat|ustat regular
expression.
%clock Trace system calls that read or modify
system clocks.
%pure Trace syscalls that always succeed and have
no arguments. Currently, this list includes
arc_gettls(2), getdtablesize(2), getegid(2),
getegid32(2), geteuid(2), geteuid32(2),
getgid(2), getgid32(2), getpagesize(2),
getpgrp(2), getpid(2), getppid(2),
get_thread_area(2) (on architectures other
than x86), gettid(2), get_tls(2), getuid(2),
getuid32(2), getxgid(2), getxpid(2),
getxuid(2), kern_features(2), and
metag_get_tls(2) syscalls.
The -c option is useful for determining which system
calls might be useful to trace. For example,
trace=open,close,read,write means to only trace those
four system calls. Be careful when making inferences
about the user/kernel boundary if only a subset of system
calls are being monitored. The default is trace=all.
-e signal=set
--signal=set
Trace only the specified subset of signals. The default
is signal=all. For example, signal=!SIGIO (or
signal=!io) causes SIGIO signals not to be traced.
-e status=set
--status=set
Print only system calls with the specified return status.
The default is status=all. When using the status
qualifier, because strace waits for system calls to
return before deciding whether they should be printed or
not, the traditional order of events may not be preserved
anymore. If two system calls are executed by concurrent
threads, strace will first print both the entry and exit
of the first system call to exit, regardless of their
respective entry time. The entry and exit of the second
system call to exit will be printed afterwards. Here is
an example when select(2) is called, but a different
thread calls clock_gettime(2) before select(2) finishes:
[pid 28779] 1130322148.939977 clock_gettime(CLOCK_REALTIME, {1130322148, 939977000}) = 0
[pid 28772] 1130322148.438139 select(4, [3], NULL, NULL, NULL) = 1 (in [3])
set can include the following elements:
successful Trace system calls that returned without an
error code. The -z option has the effect of
status=successful.
failed Trace system calls that returned with an
error code. The -Z option has the effect of
status=failed.
unfinished Trace system calls that did not return.
This might happen, for example, due to an
execve call in a neighbour thread.
unavailable Trace system calls that returned but strace
failed to fetch the error status.
detached Trace system calls for which strace detached
before the return.
-P path
--trace-path=path
Trace only system calls accessing path. Multiple -P
options can be used to specify several paths.
-z
--successful-only
Print only syscalls that returned without an error code.
-Z
--failed-only
Print only syscalls that returned with an error code.
Output format
-a column
--columns=column
Align return values in a specific column (default column
40).
-e abbrev=syscall_set
--abbrev=syscall_set
Abbreviate the output from printing each member of large
structures. The syntax of the syscall_set specification
is the same as in the -e trace option. The default is
abbrev=all. The -v option has the effect of abbrev=none.
-e verbose=syscall_set
--verbose=syscall_set
Dereference structures for the specified set of system
calls. The syntax of the syscall_set specification is
the same as in the -e trace option. The default is
verbose=all.
-e raw=syscall_set
--raw=syscall_set
Print raw, undecoded arguments for the specified set of
system calls. The syntax of the syscall_set
specification is the same as in the -e trace option.
This option has the effect of causing all arguments to be
printed in hexadecimal. This is mostly useful if you
don't trust the decoding or you need to know the actual
numeric value of an argument. See also -X raw option.
-e read=set
--read=set Perform a full hexadecimal and ASCII dump of all the data
read from file descriptors listed in the specified set.
For example, to see all input activity on file
descriptors 3 and 5 use -e read=3,5. Note that this is
independent from the normal tracing of the read(2) system
call which is controlled by the option -e trace=read.
-e write=set
--write=set Perform a full hexadecimal and ASCII dump of all the data
written to file descriptors listed in the specified set.
For example, to see all output activity on file
descriptors 3 and 5 use -e write=3,5. Note that this is
independent from the normal tracing of the write(2)
system call which is controlled by the option
-e trace=write.
-e quiet=set
--quiet=set
--silent=set
--silence=set
Suppress various information messages. The default is
quiet=none. set can include the following elements:
attach Suppress 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
Decode various information associated with file
descriptors. The default is decode-fds=none. set can
include the following elements:
path Print file paths.
socket Print socket protocol-specific information,
dev Print character/block device numbers.
pidfd Print PIDs associated with pidfd file
descriptors.
-e kvm=vcpu
--kvm=vcpu Print the exit reason of kvm vcpu. Requires Linux kernel
version 4.16.0 or higher.
-i
--instruction-pointer
Print the instruction pointer at the time of the system
call.
-k
--stack-traces
Print the execution stack trace of the traced processes
after each system call.
-o filename
--output=filename
Write the trace output to the file filename rather than
to stderr. filename.pid form is used if -ff option is
supplied. If the argument begins with '|' or '!', the
rest of the argument is treated as a command and all
output is piped to it. This is convenient for piping the
debugging output to a program without affecting the
redirections of executed programs. The latter is not
compatible with -ff option currently.
-A
--output-append-mode
Open the file provided in the -o option in append mode.
-q
--quiet
--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.
-qq
--quiet=attach,personality,exit
Suppress messages attaching, detaching, personality
changes, and about process exit status.
-qqq
--quiet=all Suppress all suppressible messages (please refer to the
-e quiet option description for the full list of
suppressible messages).
-r
--relative-timestamps[=precision]
Print 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 since -r option uses the
monotonic clock time for measuring time difference and
not the wall clock time, its measurements can differ from
the difference in time reported by the -t option.
-s strsize
--string-limit=strsize
Specify the maximum string size to print (the default is
32). Note that filenames are not considered strings and
are always printed in full.
--absolute-timestamps[=[[format:]format],[[precision:]precision]]
--timestamps[=[[format:]format],[[precision:]precision]]
Prefix 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
Prefix each line of the trace with the wall clock time.
-tt
--absolute-timestamps=precision:us
If given twice, the time printed will include the
microseconds.
-ttt
--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.
-T
--syscall-times[=precision]
Show 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 Print unabbreviated versions of environment, stat,
termios, etc. calls. These structures are very common
in calls and so the default behavior displays a
reasonable subset of structure members. Use this option
to get all of the gory details.
-x
--strings-in-hex=non-ascii
Print all non-ASCII strings in hexadecimal string format.
-xx
--strings-in-hex
--strings-in-hex=all
Print all strings in hexadecimal string format.
-X format
--const-print-style=format
Set the format for printing of named constants and flags.
Supported format values are:
raw Raw number output, without decoding.
abbrev Output a named constant or a set of flags
instead of the raw number if they are found.
This is the default strace behaviour.
verbose Output both the raw value and the decoded
string (as a comment).
-y
--decode-fds
--decode-fds=path
Print paths associated with file descriptor arguments.
-yy
--decode-fds=all
Print all available information associated with file
descritors: protocol-specific information associated with
socket file descriptors, block/character device number
associated with device file descriptors, and PIDs
asociated with pidfd file descriptors.
Statistics
-c
--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 -c is used with -f, only aggregate totals for
all traced processes are kept.
-C
--summary Like -c but also print regular output while processes are
running.
-O overhead
--summary-syscall-overhead =overhead
Set the overhead for tracing system calls to overhead.
This is useful for overriding the default heuristic for
guessing how much time is spent in mere measuring when
timing system calls using the -c option. The accuracy of
the heuristic can be gauged by timing a given program run
without tracing (using time(1)) and comparing the
accumulated system call time to the total produced using
-c.
The format of overhead specification is described in
section Time specification format description.
-S sortby
--summary-sort-by=sortby
Sort the output of the histogram printed by the -c option
by the specified criterion. Legal 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
Configure a set (and order) of columns being shown in the
call summary. The columns argument is a comma-separated
list with items being one of the following:
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) Syscall 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
Summarise the time difference between the beginning and
end of each system call. The default is to summarise the
system time.
Tampering
-e inject=syscall_set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_enter=delay][:delay_exit=delay][:when=expr]
--inject=syscall_set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_enter=delay][:delay_exit=delay][:when=expr]
Perform syscall tampering for the specified set of
syscalls. The syntax of the syscall_set specification is
the same as in the -e trace option.
At least one of error, retval, signal, delay_enter, or
delay_exit options has to be specified. error and retval
are mutually exclusive.
If :error=errno option is specified, a fault is injected
into a syscall invocation: the syscall number is replaced
by -1 which corresponds to an invalid syscall (unless a
syscall is specified with :syscall= option), and the
error code is specified using a symbolic errno value like
ENOSYS or a numeric value within 1..4095 range.
If :retval=value option is specified, success injection
is performed: the syscall number is replaced by -1, but a
bogus success value is returned to the callee.
If :signal=sig option is specified with either a symbolic
value like SIGSEGV or a numeric value within 1..SIGRTMAX
range, that signal is delivered on entering every syscall
specified by the set.
If :delay_enter=delay or :delay_exit=delay options are
specified, delay injection is performed: the tracee is
delayed by time period specified by delay on entering or
exiting the syscall, respectively. The format of delay
specification is described in section Time specification
format description.
If :signal=sig option is specified without :error=errno,
:retval=value or :delay_{enter,exit}=usecs options, then
only a signal sig is delivered without a syscall fault or
delay injection. Conversely, :error=errno or
:retval=value option without :delay_enter=delay,
:delay_exit=delay or :signal=sig options injects a fault
without delivering a signal or injecting a delay, etc.
If both :error=errno or :retval=value and :signal=sig
options are specified, then both a fault or success is
injected and a signal is delivered.
if :syscall=syscall option is specified, the
corresponding syscall with no side effects is injected
instead of -1. Currently, only "pure" (see -e
trace=%pure description) syscalls can be specified there.
Unless a :when=expr subexpression is specified, an
injection is being made into every invocation of each
syscall from the set.
The format of the subexpression is:
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 For every syscall from the set, perform
an injection for the syscall invocation
number first only.
first..last For every syscall from the set, perform
an injection for the syscall invocation
number first and all subsequent
invocations until the invocation number
last (inclusive).
first+ For every syscall from the set, perform
injections for the syscall invocation
number first and all subsequent
invocations.
first..last+ For every syscall from the set, perform
injections for the syscall invocation
number first and all subsequent
invocations until the invocation number
last (inclusive).
first+step For every syscall from the set, perform
injections for syscall invocations
number first, first+step,
first+step+step, and so on.
first..last+step Same as the previous, but consider only
syscall invocations with numbers up to
last (inclusive).
For example, to fail each third and subsequent chdir
syscalls with ENOENT, use
-e inject=chdir:error=ENOENT:when=3+.
The valid range for numbers first and step is 1..65535,
and for number last is 1..65534.
An injection expression can contain only one error= or
retval= specification, and only one signal=
specification. If an injection expression contains
multiple when= specifications, the last one takes
precedence.
Accounting of syscalls that are subject to injection is
done per syscall and per tracee.
Specification of syscall injection can be combined with
other syscall filtering options, for example, -P
/dev/urandom -e inject=file:error=ENOENT.
-e fault=syscall_set[:error=errno][:when=expr]
--fault=syscall_set[:error=errno][:when=expr]
Perform syscall fault injection for the specified set of
syscalls.
This is equivalent to more generic -e inject= expression
with default value of errno option set to ENOSYS.
Miscellaneous
-d
--debug Show some debugging output of strace itself on the
standard error.
-F This option is deprecated. It is retained for backward
compatibility only and may be removed in future releases.
Usage of multiple instances of -F option is still
equivalent to a single -f, and it is ignored at all if
used along with one or more instances of -f option.
-h
--help Print the help summary.
--seccomp-bpf
Try to enable use of seccomp-bpf (see seccomp(2)) to have
ptrace(2)-stops only when system calls that are being
traced occur in the traced processes. This option has no
effect unless -f/--follow-forks is also specified.
--seccomp-bpf 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. In cases when seccomp-bpf filter
setup failed, strace proceeds as usual and stops traced
processes on every system call.
-V
--version Print the version number of strace.
Time specification format description
Time values can be specified as a decimal floating point number (in a
format accepted by strtod(3)), optionally followed by one of the
following suffices that specify the unit of time: s (seconds), ms
(milliseconds), us (microseconds), or ns (nanoseconds). If no suffix
is specified, the value is interpreted as microseconds.
The described format is used for -O, -e inject=delay_enter, and -e
inject=delay_exit options.
When command exits, strace exits with the same exit status. If
command is terminated by a signal, strace terminates itself with the
same signal, so that strace can be used as a wrapper process
transparent to the invoking parent process. Note that parent-child
relationship (signal stop notifications, getppid(2) value, etc)
between traced process and its parent are not preserved unless -D is
used.
When using -p without a command, the exit status of strace is zero
unless no processes has been attached or there was an unexpected
error in doing the tracing.
If strace is installed setuid to root then the invoking user will be
able to attach to and trace processes owned by any user. In addition
setuid and setgid programs will be executed and traced with the
correct effective privileges. Since only users trusted with full
root privileges should be allowed to do these things, it only makes
sense to install strace as setuid to root when the users who can
execute it are restricted to those users who have this trust. For
example, it makes sense to install a special version of strace with
mode 'rwsr-xr--', user root and group trace, where members of the
trace group are trusted users. If you do use this feature, please
remember to install a regular non-setuid version of strace for
ordinary users to use.
On some architectures, strace supports decoding of syscalls for
processes that use different ABI rather than the one strace uses.
Specifically, in addition to decoding native ABI, strace can decode
the following ABIs on the following architectures:
┌───────────────────┬─────────────────────────┐
│Architecture │ ABIs supported │
├───────────────────┼─────────────────────────┤
│x86_64 │ i386, x32 [1]; i386 [2] │
├───────────────────┼─────────────────────────┤
│AArch64 │ ARM 32-bit EABI │
├───────────────────┼─────────────────────────┤
│PowerPC 64-bit [3] │ PowerPC 32-bit │
├───────────────────┼─────────────────────────┤
│s390x │ s390 │
├───────────────────┼─────────────────────────┤
│SPARC 64-bit │ SPARC 32-bit │
├───────────────────┼─────────────────────────┤
│TILE 64-bit │ TILE 32-bit │
└───────────────────┴─────────────────────────┘
[1] When strace is built as an x86_64 application
[2] When strace is built as an x32 application
[3] Big endian only
This support is optional and relies on ability to generate and parse
structure definitions during the build time. Please refer to the
output of the strace -V command in order to figure out what support
is available in your strace build ("non-native" refers to an ABI that
differs from the ABI strace has):
m32-mpers strace can trace and properly decode non-native 32-bit
binaries.
no-m32-mpers strace can trace, but cannot properly decode non-
native 32-bit binaries.
mx32-mpers strace can trace and properly decode non-native
32-on-64-bit binaries.
no-mx32-mpers strace can trace, but cannot properly decode non-
native 32-on-64-bit binaries.
If the output contains neither m32-mpers nor no-m32-mpers, then
decoding of non-native 32-bit binaries is not implemented at all or
not applicable.
Likewise, if the output contains neither mx32-mpers nor no-
mx32-mpers, then decoding of non-native 32-on-64-bit binaries is not
implemented at all or not applicable.
It is a pity that so much tracing clutter is produced by systems
employing shared libraries.
It is instructive to think about system call inputs and outputs as
data-flow across the user/kernel boundary. Because user-space and
kernel-space are separate and address-protected, it is sometimes
possible to make deductive inferences about process behavior using
inputs and outputs as propositions.
In some cases, a system call will differ from the documented behavior
or have a different name. For example, the faccessat(2) system call
does not have flags argument, and the setrlimit(2) library function
uses prlimit64(2) system call on modern (2.6.38+) kernels. These
discrepancies are normal but idiosyncratic characteristics of the
system call interface and are accounted for by C library wrapper
functions.
Some system calls have different names in different architectures and
personalities. In these cases, system call filtering and printing
uses the names that match corresponding __NR_* kernel macros of the
tracee's architecture and personality. There are two exceptions from
this general rule: arm_fadvise64_64(2) ARM syscall and
xtensa_fadvise64_64(2) Xtensa syscall are filtered and printed as
fadvise64_64(2).
On x32, syscalls that are intended to be used by 64-bit processes and
not x32 ones (for example, readv(2), that has syscall number 19 on
x86_64, with its x32 counterpart has syscall number 515), but called
with __X32_SYSCALL_BIT flag being set, are designated with #64
suffix.
On some platforms a process that is attached to with the -p option
may observe a spurious EINTR return from the current system call that
is not restartable. (Ideally, all system calls should be restarted
on strace attach, making the attach invisible to the traced process,
but a few system calls aren't. Arguably, every instance of such
behavior is a kernel bug.) This may have an unpredictable effect on
the process if the process takes no action to restart the system
call.
As strace executes the specified command directly and does not employ
a shell for that, scripts without shebang that usually run just fine
when invoked by shell fail to execute with ENOEXEC error. It is
advisable to manually supply a shell as a command with the script as
its argument.
Programs that use the setuid bit do not have effective user ID
privileges while being traced.
A traced process runs slowly.
Traced processes which are descended from command may be left running
after an interrupt signal (CTRL-C).
The original strace was written by Paul Kranenburg for SunOS and was
inspired by its trace utility. The SunOS version of strace was
ported to Linux and enhanced by Branko Lankester, who also wrote the
Linux kernel support. Even though Paul released strace 2.5 in 1992,
Branko's work was based on Paul's strace 1.5 release from 1991. In
1993, Rick Sladkey merged strace 2.5 for SunOS and the second release
of strace for Linux, added many of the features of truss(1) from
SVR4, and produced an strace that worked on both platforms. In 1994
Rick ported strace to SVR4 and Solaris and wrote the automatic
configuration support. In 1995 he ported strace to Irix and tired of
writing about himself in the third person.
Beginning with 1996, strace was maintained by Wichert Akkerman.
During his tenure, strace development migrated to CVS; ports to
FreeBSD and many architectures on Linux (including ARM, IA-64, MIPS,
PA-RISC, PowerPC, s390, SPARC) were introduced. In 2002, the burden
of strace maintainership was transferred to Roland McGrath. Since
then, strace gained support for several new Linux architectures
(AMD64, s390x, SuperH), bi-architecture support for some of them, and
received numerous additions and improvements in syscalls decoders on
Linux; strace development migrated to git during that period. Since
2009, strace is actively maintained by Dmitry Levin. strace gained
support for AArch64, ARC, AVR32, Blackfin, Meta, Nios II, 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 strace gained support
for path tracing and file descriptor path decoding. In 2014, support
for stack traces printing was added. In 2016, syscall fault
injection was implemented.
For the additional information, please refer to the NEWS file and
strace repository commit log.
Problems with strace should be reported to the strace mailing list
⟨mailto:strace-devel@lists.strace.io⟩.
strace-log-merge(1), ltrace(1), perf-trace(1), trace-cmd(1), time(1),
ptrace(2), proc(5)
strace Home Page ⟨https://strace.io/⟩
The complete list of strace contributors can be found in the CREDITS
file.
This page is part of the strace (system call tracer) project.
Information about the project can be found at ⟨http://strace.io/⟩.
If you have a bug report for this manual page, send it to
strace-devel@lists.sourceforge.net. This page was obtained from the
project's upstream Git repository
⟨https://github.com/strace/strace.git⟩ on 2020-08-13. (At that time,
the date of the most recent commit that was found in the repository
was 2020-08-06.) If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-to-
date source for the page, or you have corrections or improvements to
the information in this COLOPHON (which is not part of the original
manual page), send a mail to man-pages@man7.org
strace 5.8.0.1.c88ad 2020-06-16 STRACE(1)
Pages that refer to this page: ltrace(1) , strace-log-merge(1) , ptrace(2) , seccomp(2) , proc(5) , procfs(5) , capabilities(7) , vdso(7)