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Section: User Commands (1)
Updated: January 2013
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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




Its use is very similar to strace(1).



-a, --align column
-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, --demangle
-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 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.
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 @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
-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.
-s strsize
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.
-u username
-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 malloc+free-@libc.so*

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 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.





If you would like to report a bug, send a message to the mailing list (ltrace-devel@lists.alioth.debian.org), or use the reportbug(1) program if you are under the Debian GNU/Linux distribution.



System configuration file
Personal config file, overrides /etc/ltrace.conf



Juan Cespedes <cespedes@debian.org>
Petr Machata <pmachata@redhat.com>



ltrace.conf(5), strace(1), ptrace(2)




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