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STRACE(1) General Commands Manual STRACE(1)
NAME
strace - trace system calls and signals
SYNOPSIS
strace [-ACdffhikqqrtttTvVwxxyyzZ] [-I n] [-b execve] [-e expr]... [-a column] [-o file]
[-s strsize] [-X format] [-P path]... [-p pid]... [--seccomp-bpf] { -p pid | [-DDD]
[-E var[=val]]... [-u username] command [args] }
strace -c [-dfwzZ] [-I n] [-b execve] [-e expr]... [-O overhead] [-S sortby] [-P path]...
[-p pid]... [--seccomp-bpf] { -p pid | [-DDD] [-E var[=val]]... [-u username]
command [args] }
DESCRIPTION
In the simplest case strace runs the specified command until it exits. It intercepts and
records the system calls which are called by a process and the signals which are received
by a process. The name of each system call, its arguments and its return value are
printed on standard error or to the file specified with the -o option.
strace is a useful diagnostic, instructional, and debugging tool. System administrators,
diagnosticians and trouble-shooters will find it invaluable for solving problems with pro-
grams for which the source is not readily available since they do not need to be recom-
piled 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 paren-
theses 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 dif-
ferent 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 per-
forming ">>xyzzy" output redirection:
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
Here, the third argument of open(2) is decoded by breaking down the flag argument into its
three bitwise-OR constituents and printing the mode value in octal by tradition. Where
the traditional or native usage differs from ANSI or POSIX, the latter forms are pre-
ferred. 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 es-
sence 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 ar-
gument 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 pro-
duces 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 follow-
ing 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 com-
mand id(1) on a system with supplementary group ids:
getgroups(32, [100, 0]) = 2
On the other hand, bit-sets are also shown using square brackets, but set elements are
separated only by a space. Here is the shell, preparing to execute an external command:
sigprocmask(SIG_BLOCK, [CHLD TTOU], []) = 0
Here, the second argument is a bit-set of two signals, SIGCHLD and SIGTTOU. In some
cases, the bit-set is so full that printing out the unset elements is more valuable. In
that case, the bit-set is prefixed by a tilde like this:
sigprocmask(SIG_UNBLOCK, ~[], NULL) = 0
Here, the second argument represents the full set of all signals.
OPTIONS
General
-e expr A qualifying expression which modifies which events to trace or how to trace
them. The format of the expression is:
[qualifier=][!]value[,value]...
where qualifier is one of trace, abbrev, verbose, raw, signal, read, write,
fault, inject, status, or kvm, and value is a qualifier-dependent symbol or
number. The default qualifier is trace. Using an exclamation mark negates
the set of values. For example, -e open means literally -e trace=open which
in turn means trace only the open system call. By contrast, -e trace=!open
means to trace every system call except open. In addition, the special values
all and none have the obvious meanings.
Note that some shells use the exclamation point for history expansion even in-
side 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 pro-
cesses 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 execu-
tion 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 Run tracer process as a grandchild, not as the parent of the tracee. This re-
duces the visible effect of strace by keeping the tracee a direct child of the
calling process.
-DD Run tracer process as tracee's grandchild in a separate process group. In ad-
dition to reduction of the visible effect of strace, it also avoids killing of
strace with kill(2) issued to the whole process group.
-DDD Run tracer process as tracee's grandchild in a separate session ("true daemon-
isation"). In addition to reduction of the visible effect of strace, it also
avoids killing of strace upon session termination.
-f Trace child processes as they are created by currently traced processes as a
result of the fork(2), vfork(2) and clone(2) system calls. Note that -p PID
-f will attach all threads of process PID if it is multi-threaded, not only
thread with thread_id = PID.
-ff If the -o filename option is in effect, each processes trace is written to
filename.pid where pid is the numeric process id of each process. This is in-
compatible with -c, since no per-process counts are kept.
One might want to consider using strace-log-merge(1) to obtain a combined
strace log view.
-I interruptible
When strace can be interrupted by signals (such as pressing CTRL-C).
1 no signals are blocked;
2 fatal signals are blocked while decoding syscall (default);
3 fatal signals are always blocked (default if -o FILE PROG);
4 fatal signals and SIGTSTP (CTRL-Z) are always blocked (useful to make
strace -o FILE PROG not stop on CTRL-Z, default if -D).
Filtering
-e trace=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 all system calls which involve process management. This is
useful for watching the fork, wait, and exec steps of a process.
The syntax without a preceding percent sign ("-e trace=process")
is deprecated.
%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 pre-
ceding percent sign ("-e trace=signal") is deprecated.
%ipc
ipc Trace all IPC related system calls. The syntax without a preced-
ing percent sign ("-e trace=ipc") is deprecated.
%desc
desc Trace all file descriptor related system calls. The syntax with-
out a preceding percent sign ("-e trace=desc") is deprecated.
%memory
memory Trace all memory mapping related system calls. The syntax with-
out 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 and fstatat syscall variants.
%%stat Trace syscalls used for requesting file status (stat, lstat, fs-
tat, 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_fs-
tatfs64 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.
%pure Trace syscalls that always succeed and have no arguments. Cur-
rently, this list includes arc_gettls(2), getdtablesize(2), gete-
gid(2), getegid32(2), geteuid(2), geteuid32(2), getgid(2), get-
gid32(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 sta-
tus=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 op-
tion 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 Print only syscalls that returned without an error code.
-Z 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 syn-
tax 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 de-
fault 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 hexadeci-
mal. 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 de-
scriptors 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 de-
scriptors listed in the specified set. For example, to see all output activ-
ity on file descriptors 3 and 5 use -e write=3,5. Note that this is indepen-
dent from the normal tracing of the write(2) system call which is controlled
by the option -e trace=write.
-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. file-
name.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 Suppress messages about attaching, detaching etc. This happens automatically
when output is redirected to a file and the command is run directly instead of
attaching.
-qq If given twice, suppress messages about process exit status.
-r Print a relative timestamp upon entry to each system call. This records the
time difference between the beginning of successive system calls. Note that
since -r option uses the monotonic clock time for measuring time difference
and not the wall clock time, its measurements can differ from the difference
in time reported by the -t option.
-s strsize
--string-limit=strsize
Specify the maximum string size to print (the default is 32). Note that file-
names are not considered strings and are always printed in full.
-t Prefix each line of the trace with the wall clock time.
-tt If given twice, the time printed will include the microseconds.
-ttt If given thrice, the time printed will include the microseconds and the lead-
ing portion will be printed as the number of seconds since the epoch.
-T Show the time spent in system calls. This records the time difference between
the beginning and the end of each system call.
-v
--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 Print all non-ASCII strings in hexadecimal string format.
-xx 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 Print paths associated with file descriptor arguments.
-yy Print protocol specific information associated with socket file descriptors,
and block/character device number associated with device file descriptors.
Statistics
-c
--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 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 specifica-
tion 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_total or total_time), calls (or
count), errors (or error), name (or syscall or syscall_name), and nothing (or
none); default is time.
-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][:de-
lay_enter=delay][:delay_exit=delay][:when=expr]
--inject=syscall_set[:error=errno|:retval=value][:signal=sig][:syscall=syscall][:delay_en-
ter=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 invo-
cation: 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 en-
tering every syscall specified by the set.
If :delay_enter=delay or :delay_exit=delay options are specified, delay injec-
tion is performed: the tracee is delayed by time period specified by delay on
entering or exiting the syscall, respectively. The format of delay specifica-
tion is described in section Time specification format description.
If :signal=sig option is specified without :error=errno, :retval=value or :de-
lay_{enter,exit}=usecs options, then only a signal sig is delivered without a
syscall fault or delay injection. Conversely, :error=errno or :retval=value
option without :delay_enter=delay, :delay_exit=delay or :signal=sig options
injects a fault without delivering a signal or injecting a delay, etc.
If both :error=errno or :retval=value and :signal=sig options are specified,
then both a fault or success is injected and a signal is delivered.
if :syscall=syscall option is specified, the corresponding syscall with no
side effects is injected instead of -1. Currently, only "pure" (see -e
trace=%pure description) syscalls can be specified there.
Unless a :when=expr subexpression is specified, an injection is being made
into every invocation of each syscall from the set.
The format of the subexpression is one of the following:
first For every syscall from the set, perform an injection for the
syscall invocation number first only.
first+ For every syscall from the set, perform injections for the syscall
invocation number first and all subsequent invocations.
first+step For every syscall from the set, perform injections for syscall in-
vocations number first, first+step, first+step+step, and so on.
For example, to fail each third and subsequent chdir syscalls with ENOENT, use
-e inject=chdir:error=ENOENT:when=3+.
The valid range for numbers first and step is 1..65535.
An injection expression can contain only one error= or retval= specification,
and only one signal= specification. If an injection expression contains mul-
tiple 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 filter-
ing 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
Enable (experimental) usage of seccomp-bpf (see seccomp(2)) to have
ptrace(2)-stops only when system calls that are being traced occur in the
traced processes. Implies the -f option. An attempt to rely on seccomp-bpf
to filter system calls may fail for various reasons, e.g. there are too many
system calls to filter, the seccomp API is not available, or strace itself is
being traced. --seccomp-bpf is also ineffective on processes attached using
-p. In cases when seccomp-bpf filter setup failed, strace proceeds as usual
and stops traced processes on every system call.
-V
--version Print the version number of strace.
Time specification format description
Time values can be specified as a decimal floating point number (in a format accepted by
strtod(3)), optionally followed by one of the following suffices that specify the unit of
time: s (seconds), ms (milliseconds), us (microseconds), or ns (nanoseconds). If no suf-
fix is specified, the value is interpreted as microseconds.
The described format is used for -O, -e inject=delay_enter, and -e inject=delay_exit op-
tions.
DIAGNOSTICS
When command exits, strace exits with the same exit status. If command is terminated by a
signal, strace terminates itself with the same signal, so that strace can be used as a
wrapper process transparent to the invoking parent process. Note that parent-child rela-
tionship (signal stop notifications, getppid(2) value, etc) between traced process and its
parent are not preserved unless -D is used.
When using -p without a command, the exit status of strace is zero unless no processes has
been attached or there was an unexpected error in doing the tracing.
SETUID INSTALLATION
If strace is installed setuid to root then the invoking user will be able to attach to and
trace processes owned by any user. In addition setuid and setgid programs will be exe-
cuted 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-se-
tuid version of strace for ordinary users to use.
MULTIPLE PERSONALITIES SUPPORT
On some architectures, strace supports decoding of syscalls for processes that use differ-
ent 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 bina-
ries.
If the output contains neither m32-mpers nor no-m32-mpers, then decoding of non-native
32-bit binaries is not implemented at all or not applicable.
Likewise, if the output contains neither mx32-mpers nor no-mx32-mpers, then decoding of
non-native 32-on-64-bit binaries is not implemented at all or not applicable.
NOTES
It is a pity that so much tracing clutter is produced by systems employing shared li-
braries.
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-pro-
tected, 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 inter-
face 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 excep-
tions from this general rule: arm_fadvise64_64(2) ARM syscall and xtensa_fadvise64_64(2)
Xtensa syscall are filtered and printed as fadvise64_64(2).
On x32, syscalls that are intended to be used by 64-bit processes and not x32 ones (for
example, readv(2), that has syscall number 19 on x86_64, with its x32 counterpart has
syscall number 515), but called with __X32_SYSCALL_BIT flag being set, are designated with
#64 suffix.
On some platforms a process that is attached to with the -p option may observe a spurious
EINTR return from the current system call that is not restartable. (Ideally, all system
calls should be restarted on strace attach, making the attach invisible to the traced
process, but a few system calls aren't. Arguably, every instance of such behavior is a
kernel bug.) This may have an unpredictable effect on the process if the process takes no
action to restart the system call.
As strace executes the specified command directly and does not employ a shell for that,
scripts without shebang that usually run just fine when invoked by shell fail to execute
with ENOEXEC error. It is advisable to manually supply a shell as a command with the
script as its argument.
BUGS
Programs that use the setuid bit do not have effective user ID privileges while being
traced.
A traced process runs slowly.
Traced processes which are descended from command may be left running after an interrupt
signal (CTRL-C).
HISTORY
The original strace was written by Paul Kranenburg for SunOS and was inspired by its trace
utility. The SunOS version of strace was ported to Linux and enhanced by Branko
Lankester, who also wrote the Linux kernel support. Even though Paul released strace 2.5
in 1992, Branko's work was based on Paul's strace 1.5 release from 1991. In 1993, Rick
Sladkey merged strace 2.5 for SunOS and the second release of strace for Linux, added many
of the features of truss(1) from SVR4, and produced an strace that worked on both plat-
forms. In 1994 Rick ported strace to SVR4 and Solaris and wrote the automatic configura-
tion 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 sup-
port 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 ac-
tively maintained by Dmitry Levin. strace gained support for AArch64, ARC, AVR32, Black-
fin, Meta, Nios II, OpenSISC 1000, RISC-V, Tile/TileGx, Xtensa architectures since that
time. In 2012, unmaintained and apparently broken support for non-Linux operating systems
was removed. Also, in 2012 strace gained support for path tracing and file descriptor
path decoding. In 2014, support for stack traces printing was added. In 2016, syscall
fault injection was implemented.
For the additional information, please refer to the NEWS file and strace repository commit
log.
REPORTING BUGS
Problems with strace should be reported to the strace mailing list
<mailto:strace-devel AT lists.io>.
SEE ALSO
strace-log-merge(1), ltrace(1), perf-trace(1), trace-cmd(1), time(1), ptrace(2), proc(5)
strace Home Page <https://strace.io/>
AUTHORS
The complete list of strace contributors can be found in the CREDITS file.
strace 5.5 2020-02-04 STRACE(1)
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