.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-.\"
-.\" $Id$
-.\"
.de CW
.sp
.nf
.fi
.sp
..
+.\" Macro IX is not defined in the groff macros
+.if \n(.g \{\
+. de IX
+..
+.\}
.TH STRACE 1 "2010-03-30"
.SH NAME
strace \- trace system calls and signals
.SH SYNOPSIS
.B strace
-[
-.B \-CdDffhiqrtttTvxxy
-]
-[
-.BI \-a column
-]
-[
-.BI \-e expr
-]
-\&...
-[
-.BI \-o file
-]
-[
-.BI \-p pid
-]
-\&...
-[
-.BI \-P path
-]
-\&...
-[
-.BI \-s strsize
-]
-[
-.BI \-u username
-]
-[
-.BI \-E var=val
-]
-\&...
-[
-.BI \-E var
-]
-\&...
-[
-.I command
-[
-.I arg
-\&...
-]
-]
+[\fB-CdffhikqrtttTvVxxy\fR]
+[\fB-I\fIn\fR]
+[\fB-b\fIexecve\fR]
+[\fB-e\fIexpr\fR]...
+[\fB-a\fIcolumn\fR]
+[\fB-o\fIfile\fR]
+[\fB-s\fIstrsize\fR]
+[\fB-P\fIpath\fR]... \fB-p\fIpid\fR... /
+[\fB-D\fR]
+[\fB-E\fIvar\fR[=\fIval\fR]]... [\fB-u\fIusername\fR]
+\fIcommand\fR [\fIargs\fR]
.sp
.B strace
-.B \-c
-[
-.B \-D
-]
-[
-.BI \-e expr
-]
-\&...
-[
-.BI \-O overhead
-]
-[
-.BI \-S sortby
-]
-[
-.I command
-[
-.I arg
-\&...
-]
-]
+\fB-c\fR[\fBdf\fR]
+[\fB-I\fIn\fR]
+[\fB-b\fIexecve\fR]
+[\fB-e\fIexpr\fR]...
+[\fB-O\fIoverhead\fR]
+[\fB-S\fIsortby\fR] \fB-p\fIpid\fR... /
+[\fB-D\fR]
+[\fB-E\fIvar\fR[=\fIval\fR]]... [\fB-u\fIusername\fR]
+\fIcommand\fR [\fIargs\fR]
.SH DESCRIPTION
.IX "strace command" "" "\fLstrace\fR command"
.LP
.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:
+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)
+open("/foo/bar", O_RDONLY) = \-1 ENOENT (No such file or directory)
.CE
-Signals are printed as a signal symbol and a signal string.
-An excerpt from stracing and interrupting the command ``sleep 666'' is:
+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 (Interrupt) ---
+--- 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
immediate reexecution after the signal handler completes.
.CW
read(0, 0x7ffff72cf5cf, 1) = ? ERESTARTSYS (To be restarted)
---- SIGALRM (Alarm clock) @ 0 (0) ---
+--- SIGALRM ... ---
rt_sigreturn(0xe) = 0
-read(0, ""..., 1) = 0
+read(0, "", 1) = 0
.CE
Arguments are printed in symbolic form with a passion.
-This example shows the shell performing ``>>xyzzy'' output redirection:
+This example shows the shell performing ">>xyzzy" output redirection:
.CW
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
.CE
Structure pointers are dereferenced and the members are displayed
as appropriate. In all 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:
+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(1, 3), ...}) = 0
.CE
-Notice how the `struct stat' argument is dereferenced and how each member is
+Notice how the 'struct stat' argument is dereferenced and how each member is
displayed symbolically. In particular, observe how the st_mode member
is carefully decoded into a bitwise-OR of symbolic and numeric values.
Also notice in this example that the first argument to lstat is an input
to the system call and the second argument is an output. Since output
arguments are not modified if the system call fails, arguments may not
-always be dereferenced. For example, retrying the ``ls \-l'' example
+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)
+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
.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
+Here is a line from "ls \-l" where the
.B getpwuid
library routine is reading the password file:
.CW
.CE
While structures are annotated using curly braces, simple pointers
and arrays are printed using square brackets with commas separating
-elements. Here is an example from the command ``id'' on a system with
+elements. Here is an example from the command "id" on a system with
supplementary group ids:
.CW
getgroups(32, [100, 0]) = 2
but also print regular output while processes are running.
.TP
.B \-D
-(Not available on SVR4 and FreeBSD.)
Run tracer process as a detached grandchild, not as parent of the
tracee. This reduces the visible effect of
.B strace
.B \-f
Trace child processes as they are created by currently traced
processes as a result of the
-.BR fork (2)
-system call.
-.IP
-On non-Linux platforms the new process is
-attached to as soon as its pid is known (through the return value of
-.BR fork (2)
-in the parent process). This means that such children may run
-uncontrolled for a while (especially in the case of a
-.BR vfork (2)),
-until the parent is scheduled again to complete its
-.RB ( v ) fork (2)
-call. On Linux the child is traced from its first instruction with no delay.
-If the parent process decides to
-.BR wait (2)
-for a child that is currently
-being traced, it is suspended until an appropriate child process either
-terminates or incurs a signal that would cause it to terminate (as
-determined from the child's current signal disposition).
-.IP
-On SunOS 4.x the tracing of
-.BR vfork s
-is accomplished with some dynamic linking trickery.
+.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 PID if it is multi-threaded,
+not only thread with thread_id = PID.
.TP
.B \-ff
If the
.B \-i
Print the instruction pointer at the time of the system call.
.TP
+.B \-k
+Print the execution stack trace of the traced processes after each system call (experimental).
+.TP
.B \-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.
.TP
+.B \-qq
+If given twice, suppress messages about process exit status.
+.TP
.B \-r
Print a relative timestamp upon entry to each system call. This
records the time difference between the beginning of successive
of seconds since the epoch.
.TP
.B \-T
-Show the time spent in system calls. This records the time
+Show the time spent in system calls. This records the time
difference between the beginning and the end of each system call.
.TP
+.B \-w
+Summarise the time difference between the beginning and end of
+each system call. The default is to summarise the system time.
+.TP
.B \-v
Print unabbreviated versions of environment, stat, termios, etc.
calls. These structures are very common in calls and so the default
.B \-y
Print paths associated with file descriptor arguments.
.TP
+.B \-yy
+Print ip:port pairs associated with socket file descriptors.
+.TP
.BI "\-a " column
Align return values in a specific column (default column 40).
.TP
+.BI "\-b " syscall
+If specified syscall is reached, detach from traced process.
+Currently, only
+.I execve
+syscall is supported. This option is useful if you want to trace
+multi-threaded process and therefore require -f, but don't want
+to trace its (potentially very complex) children.
+.TP
.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]\fIvalue1\fR[\fB,\fIvalue2\fR]...
+[\,\fIqualifier\/\fB=\fR][\fB!\fR]\,\fIvalue1\/\fR[\fB,\,\fIvalue2\/\fR]...
.RE
.IP
where
expansion even inside quoted arguments. If so, you must escape
the exclamation point with a backslash.
.TP
-\fB\-e\ trace\fR=\fIset\fR
+\fB\-e\ trace\fR=\,\fIset\fR
Trace only the specified set of system calls. The
.B \-c
option is useful for determining which system calls might be useful
.BR "\-e\ trace" = desc
Trace all file descriptor related system calls.
.TP
-\fB\-e\ abbrev\fR=\fIset\fR
+.BR "\-e\ trace" = memory
+Trace all memory mapping related system calls.
+.TP
+\fB\-e\ abbrev\fR=\,\fIset\fR
Abbreviate the output from printing each member of large structures.
The default is
.BR abbrev = all .
option has the effect of
.BR abbrev = none .
.TP
-\fB\-e\ verbose\fR=\fIset\fR
+\fB\-e\ verbose\fR=\,\fIset\fR
Dereference structures for the specified set of system calls. The
default is
.BR verbose = all .
.TP
-\fB\-e\ raw\fR=\fIset\fR
+\fB\-e\ raw\fR=\,\fIset\fR
Print raw, undecoded arguments for the specified set of system calls.
This option has the effect of causing all arguments to be printed
in hexadecimal. This is mostly useful if you don't trust the
decoding or you need to know the actual numeric value of an
argument.
.TP
-\fB\-e\ signal\fR=\fIset\fR
+\fB\-e\ signal\fR=\,\fIset\fR
Trace only the specified subset of signals. The default is
.BR signal = all .
For example,
.BR signal "=!" io )
causes SIGIO signals not to be traced.
.TP
-\fB\-e\ read\fR=\fIset\fR
+\fB\-e\ 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
and
.I 5
use
-\fB\-e\ read\fR=\fI3\fR,\fI5\fR.
+\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
+\fB\-e\ 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
and
.I 5
use
-\fB\-e\ write\fR=\fI3\fR,\fI5\fR.
+\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
+.BI "\-I " interruptible
+When strace can be interrupted by signals (such as pressing ^C).
+1: no signals are blocked; 2: fatal signals are blocked while decoding syscall
+(default); 3: fatal signals are always blocked (default if '-o FILE PROG');
+4: fatal signals and SIGTSTP (^Z) are always blocked (useful to make
+strace -o FILE PROG not stop on ^Z).
+.TP
.BI "\-o " filename
Write the trace output to the file
.I filename
if
.B \-ff
is used.
-If the argument begins with `|' or with `!' then the rest of the
+If the argument begins with '|' or with '!' then 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.
leaving it (them) to continue running.
Multiple
.B \-p
-options can be used to attach to up to 32 processes in addition to
-.I command
-(which is optional if at least one
-.B \-p
-option is given).
+options can be used to attach to many processes.
+-p "`pidof PROG`" syntax is supported.
.TP
.BI "\-P " path
Trace only system calls accessing
.I path.
Multiple
.B \-P
-options can be used to specify up to 256 paths.
+options can be used to specify several paths.
.TP
.BI "\-s " strsize
Specify the maximum string size to print (the default is 32). Note
Unless this option is used setuid and setgid programs are executed
without effective privileges.
.TP
-\fB\-E\ \fIvar\fR=\fIval\fR
+\fB\-E\ \fIvar\fR=\,\fIval\fR
Run command with
.IR var = val
in its list of environment variables.
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,
+getppid() value, etc) between traced process and its parent are not preserved
+unless
+.B \-D
+is used.
.LP
When using
.BR \-p ,
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
+with mode 'rwsr-xr--', user
.B root
and group
.BR trace ,
system call interface and are accounted for by C library wrapper
functions.
.LP
-On some platforms a process that has a system call trace applied
-to it with the
+On some platforms a process that is attached to with the
.B \-p
-option will receive a
-.BR \s-1SIGSTOP\s0 .
-This signal may interrupt a system call that is not restartable.
+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.
.SH BUGS
.SM ID
privileges while being traced.
.LP
-A traced process ignores
-.SM SIGSTOP
-except on SVR4 platforms.
-.LP
-A traced process which tries to block SIGTRAP will be sent a SIGSTOP
-in an attempt to force continuation of tracing.
-.LP
A traced process runs slowly.
.LP
Traced processes which are descended from
may be left running after an interrupt signal (\c
.SM CTRL\s0-C).
.LP
-On Linux, exciting as it would be, tracing the init process is forbidden.
-.LP
The
.B \-i
option is weakly supported.
.SH HISTORY
-.B strace
The original
.B strace
was written by Paul Kranenburg
.B strace
to Irix
and tired of writing about himself in the third person.
-.SH BUGS
-The SIGTRAP signal is used internally by the kernel implementation of
-system call tracing. When a traced process receives a SIGTRAP signal not
-associated with tracing, strace will not report that signal correctly.
-This signal is not normally used by programs, but could be via a hard-coded
-break instruction or via
-.BR kill (2).
.SH PROBLEMS
Problems with
.B strace
-should be reported via the Debian Bug Tracking System,
-or to the
+should be reported to the
.B strace
mailing list at <strace\-devel@lists.sourceforge.net>.
projects / strace / blobdiff