ltrace - A library call tracer
] [-S] [-b|--no-signals] [-i] [-w|--where= nr
[-r|-t|-tt|-ttt] [-T] [-F filename
] [-A maxelts
] [-C|--demangle] [-a|--align column
] [-o|--output filename
] [-D|--debug mask
] [-f] [-p pid
] [[--] command [arg ...]
-c [-e filter
] [-S] [-o|--output filename
] [-f] [-p pid
command [arg ...]
is a program that simply runs the specified command
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
- -A maxelts
- Maximum number of array elements to print before suppressing the rest with
an ellipsis ("..."). This also limits number of recursive
- -b, --no-signals
- Disable printing of signals recieved by the traced process.
- Count time and calls for each library call and report a summary on program
- -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.
- 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
- -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
- -h, --help
- Show a summary of the options to ltrace and exit.
- 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.
- When no -e option is given, don't assume the default action of
- -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
- -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
- 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).
- Display system calls as well as library calls
- Prefix each line of the trace with the time of day.
- If given twice, the time printed will include the microseconds.
- If given thrice, the time printed will include the microseconds and the
leading portion will be printed as the number of seconds since the
- 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:
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
is used to match symbol names, library_pattern
match library SONAMEs. Both are implicitly globs, but can be regular
expressions as well (see below). The glob syntax supports meta-characters
and character classes, similarly to what basic bash
globs support. ^
are recognized to mean, respectively,
start and end of given name.
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 *
is really malloc@*
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
. In addition to that, special library pattern MAIN
matches symbols in the main binary and never a library with actual SONAME
(use e.g. ^MAIN
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
, 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
in front of it, which has the effect of tracing complement of
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
. If it matches a +
rule, it becomes marked
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
(firstname.lastname@example.org), or use the reportbug(1)
if you are under the Debian GNU/Linux distribution.
- System configuration file
- Personal config file, overrides /etc/ltrace.conf
Juan Cespedes <email@example.com>
Petr Machata <firstname.lastname@example.org>