ltrace - A library call tracer
ltrace [-e
filter|-L] [-l|--library=
library_pattern] [-x
filter] [-S] [-b|--no-signals] [-i] [-w|--where=
nr]
[-r|-t|-tt|-ttt] [-T] [-F
filename] [-A
maxelts] [-s
strsize] [-C|--demangle] [-a|--align
column] [-n|--indent
nr] [-o|--output
filename] [-D|--debug
mask] [-u
username] [-f] [-p
pid] [[--]
command [arg ...]]
ltrace -c [-e
filter|-L] [-l|--library=
library_pattern] [-x
filter] [-S] [-o|--output
filename] [-f] [-p
pid] [[--]
command [arg ...]]
ltrace -V|--version
ltrace -h|--help
ltrace is a program that simply runs the specified
command until
it exits. It intercepts and records the dynamic library calls which are called
by the executed process and the signals which are received by that process. It
can also intercept and print the system calls executed by the program.
Its use is very similar to
strace(1).
- -a, --align column
- Align return values in a specific column (default
column is 5/8 of screen width).
- -A maxelts
- Maximum number of array elements to print before
suppressing the rest with an ellipsis ("..."). This also limits
number of recursive structure expansions.
- -b, --no-signals
- Disable printing of signals recieved by the traced
process.
- -c
- Count time and calls for each library call and report a
summary on program exit.
- -C, --demangle
- Decode (demangle) low-level symbol names into user-level
names. Besides removing any initial underscore prefix used by the system,
this makes C++ function names readable.
- -D, --debug mask
- Show debugging output of ltrace itself. mask
is a number with internal meaning that's not really well defined at all.
mask of 77 shows all debug messages, which is what you usually
need.
- -e filter
- A qualifying expression which modifies which library calls
to trace. The format of the filter expression is described in the section
FILTER EXPRESSIONS. If more than one -e option appears on the
command line, the library calls that match any of them are traced. If no
-e is given, @MAIN is assumed as a default.
- -f
- Trace child processes as they are created by currently
traced processes as a result of the fork(2) or clone(2) system calls. The
new process is attached immediately.
- -F filename
- Load an alternate config file. Normally, /etc/ltrace.conf
and ~/.ltrace.conf will be read (the latter only if it exists). Use this
option to load the given file or files instead of those two default files.
See ltrace.conf(5) for details on the syntax of ltrace configuration
files.
- -h, --help
- Show a summary of the options to ltrace and exit.
- -i
- Print the instruction pointer at the time of the library
call.
- -l, --library library_pattern
- Display only calls to functions implemented by libraries
that match library_pattern. Multiple library patters can be
specified with several instances of this option. Syntax of library_pattern
is described in section FILTER EXPRESSIONS.
Note that while this option selects calls that might be directed to the
selected libraries, there's no actual guarantee that the call won't be
directed elsewhere due to e.g. LD_PRELOAD or simply dependency ordering.
If you want to make sure that symbols in given library are actually
called, use -x @library_pattern instead.
- -L
- When no -e option is given, don't assume the default action
of @MAIN.
- -n, --indent nr
- Indent trace output by nr spaces for each level of
call nesting. Using this option makes the program flow visualization easy
to follow. This indents uselessly also functions that never return, such
as service functions for throwing exceptions in the C++ runtime.
- -o, --output filename
- Write the trace output to the file filename rather
than to stderr.
- -p pid
- Attach to the process with the process ID pid and
begin tracing. This option can be used together with passing a command to
execute. It is possible to attach to several processes by passing more
than one option -p.
- -r
- Print a relative timestamp with each line of the trace.
This records the time difference between the beginning of successive
lines.
- -s strsize
- Specify the maximum string size to print (the default is
32).
- -S
- Display system calls as well as library calls
- -t
- Prefix each line of the trace with the time of day.
- -tt
- If given twice, the time printed will include the
microseconds.
- -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.
- -T
- Show the time spent inside each call. This records the time
difference between the beginning and the end of each call.
- -u username
- Run command with the userid, groupid 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.
- -w, --where nr
- Show backtrace of nr stack frames for each traced
function. This option enabled only if libunwind support was enabled at
compile time.
- -x filter
- A qualifying expression which modifies which symbol table
entry points to trace. The format of the filter expression is described in
the section FILTER EXPRESSIONS. If more than one -x option appears
on the command line, the symbols that match any of them are traced. No
entry points are traced if no -x is given.
- -V, --version
- Show the version number of ltrace and exit.
Filter expression is a chain of glob- or regexp-based rules that are used to
pick symbols for tracing from libraries that the process uses. Most of it is
intuitive, so as an example, the following would trace calls to malloc and
free, except those done by libc:
-e
[email protected]*
This reads: trace malloc and free, but don't trace anything that comes from
libc. Semi-formally, the syntax of the above example looks approximately like
this:
{[+-][
symbol_pattern][@
library_pattern]}
Symbol_pattern is used to match symbol names,
library_pattern to
match library SONAMEs. Both are implicitly globs, but can be regular
expressions as well (see below). The glob syntax supports meta-characters
* and
? and character classes, similarly to what basic bash
globs support.
^ and
$ are recognized to mean, respectively,
start and end of given name.
Both
symbol_pattern and
library_pattern have to match the whole
name. If you want to match only part of the name, surround it with one or two
*'s as appropriate. The exception is if the pattern is not mentioned at all,
in which case it's as if the corresponding pattern were
*. (So
malloc is really
malloc@* and
@libc.* is really
*@libc.*.)
In libraries that don't have an explicit SONAME, basename is taken for SONAME.
That holds for main binary as well:
/bin/echo has an implicit SONAME of
echo. In addition to that, special library pattern
MAIN always
matches symbols in the main binary and never a library with actual SONAME
MAIN (use e.g.
^MAIN or
[M]AIN for that).
If the symbol or library pattern is surrounded in slashes (/like this/), then it
is considered a regular expression instead. As a shorthand, instead of writing
/x/@/y/, you can write
/x@y/.
If the library pattern starts with a slash, it is not a SONAME expression, but a
path expression, and is matched against the library path name.
The first rule may lack a sign, in which case
+ is assumed. If, on the
other hand, the first rule has a
- sign, it is as if there was another
rule
@ in front of it, which has the effect of tracing complement of
given rule.
The above rules are used to construct the set of traced symbols. Each candidate
symbol is passed through the chain of above rules. Initially, the symbol is
unmarked. If it matches a
+ rule, it becomes
marked, if
it matches a
- rule, it becomes
unmarked again. If, after
applying all rules, the symbol is
marked, it will be traced.
It has most of the bugs stated in
strace(1).
It only works on Linux and in a small subset of architectures.
If you would like to report a bug, send a message to the mailing list
(
[email protected]), or use the
reportbug(1) program
if you are under the Debian GNU/Linux distribution.
- /etc/ltrace.conf
- System configuration file
- ~/.ltrace.conf
- Personal config file, overrides /etc/ltrace.conf
Juan Cespedes <
[email protected]>
Petr Machata <
[email protected]>
ltrace.conf(5),
strace(1),
ptrace(2)