strace.1

linux进程跟踪的工具和源代码

.\" Copyright (c) 1991, 1992 Paul Kranenburg <[e-mail]>
.\" Copyright (c) 1993 Branko Lankester <[e-mail]>
.\" Copyright (c) 1993, 1994, 1995, 1996 Rick Sladkey <[e-mail]>
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.\"	$Id: strace.1,v 1.7 1999/12/23 14:20:15 wichert Exp $
.\"
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.TH STRACE 1 "99/06/11"
.SH NAME
strace \- trace system calls and signals
.SH SYNOPSIS
.B strace
[
.B \-dffhiqrtttTvxx
]
[
.BI \-a column
]
[
.BI \-e expr
]
\&...
[
.BI \-o file
]
[
.BI \-p pid
]
\&...
[
.BI \-s strsize
]
[
.BI \-u username
]
[
.I command
[
.I arg
\&...
]
]
.sp
.B strace
.B \-c
[
.BI \-e expr
]
\&...
[
.BI \-O overhead
]
[
.BI \-S sortby
]
[
.I command
[
.I arg
\&...
]
]
.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 adminstrators, 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 a signal symbol and a signal string.
An excerpt from stracing and interrupting the command ``sleep 666'' is:
.CW
sigsuspend([] <unfinished ...>
--- SIGINT (Interrupt) ---
+++ killed by SIGINT +++
.CE
Arguments are printed in symbolic form with a passion.
This example shows the shell peforming ``>>xyzzy'' output redirection:
.CW
open("xyzzy", O_WRONLY|O_APPEND|O_CREAT, 0666) = 3
.CE
Here the three argument form of open is decoded by breaking down the
flag argument into its three bitwise-OR constituents and printing the
mode value in octal by tradition.  Where traditional or native
usage differs from ANSI or POSIX, the latter forms are preferred.
In some cases,
.B strace
output has proven to be more readable than the source.
.LP
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:
.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
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
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
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
.B getpwuid
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, 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
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, 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
.TP 12
.TP
.B \-c
Count time, calls, and errors for each system call and report a
summary on program exit.
.TP
.B \-d
Show some debugging output of
.B strace
itself on the standard error.
.TP
.B \-f
Trace child processes as they are created by currently traced
processes as a result of the
.BR fork (2)
system call.  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.
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).
.TP
.B \-ff
If the
.B \-o
.I filename
option is in effect, each processes trace is written to
.I filename.pid
where pid is the numeric process id of each process.
.TP
.B \-F
Attempt to follow
.BR vfork s.
(On SunOS 4.x, this is accomplished with
some dynamic linking trickery.  On Linux, it requires some kernel
functionality not yet in the standard kernel.)  Otherwise,
.BR vfork s
will
not be followed even if
.B \-f
has been given.
.TP
.B \-h
Print the help summary.
.TP
.B \-i
Print the instruction pointer at the time of the system call.
.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 \-r
Print a relative timestamp upon entry to each system call.  This
records the time difference between the beginning of successive
system calls.
.TP
.B \-t
Prefix each line of the trace with the time of day.
.TP
.B \-tt
If given twice, the time printed will include the microseconds.
.TP
.B \-ttt
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
Show the time spent in system calls. This records the time
difference between the beginning and the end of each system call.
.TP
.B \-v
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
.B \-V
Print the version number of
.BR strace .
.TP
.B \-x
Print all non-ASCII strings in hexadecimal string format.
.TP
.B \-xx
Print all strings in hexadecimal string format.
.TP
.BI "\-a " column
Align return values in a specific column (default column 40).
.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]...
.RE
.IP
where
.I qualifier