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).
ltrace shows parameters of invoked functions and system calls. To
determine what arguments each function has, it needs external
declaration of function prototypes. Those are stored in files called
prototype libraries--see ltrace.conf(5) for details on the syntax of
these files. See the section PROTOTYPE LIBRARY DISCOVERY to learn
how ltrace finds prototype libraries.
-a, --align column
Align return values in a specific column (default column is
5/8 of screen width).
Maximum number of array elements to print before suppressing
the rest with an ellipsis ("..."). This also limits number of
recursive structure expansions.
Disable printing of signals received by the traced process.
-c Count time and calls for each library call and report a
summary on program exit.
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
describing which debug messages should be displayed. Use the
option -Dh to see what can be used, but note that currently
the only reliable debugmask is 77, which shows all debug
A qualifying expression which modifies which library calls
(i.e. calls done through PLT slots, which are typically calls
from the main binary to a library, or inter-library calls) to
trace. Usage examples and the syntax description appear below
in sections FILTER SPECIFICATIONS and 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, --config pathlist
Contains a colon-separated list of paths. If a path refers to
a directory, that directory is considered when prototype
libraries are searched (see the section PROTOTYPE LIBRARYDISCOVERY). If it refers to a file, that file is imported
implicitly to all loaded prototype libraries.
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. This is as if you specified one -e for
every symbol implemented in a library specified by
library_pattern. Multiple library patters can be specified
with several instances of this option. Usage examples and the
syntax description of library_pattern appear below in sections
FILTER SPECIFICATIONS and 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. In practice this means that library calls will not be
-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 -p.
-r Print a relative timestamp with each line of the trace. This
records the time difference between the beginning of
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
-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.
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
-w, --where nr
Show backtrace of nr stack frames for each traced function.
This option enabled only if elfutils or libunwind support was
enabled at compile time.
A qualifying expression which modifies which symbol table
entry points to trace (those are typically calls inside a
library or main binary, though PLT calls, traced by -e, land
on entry points as well). Usage examples and the syntax
description appear below in sections FILTER SPECIFICATIONS and
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.
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 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
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
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
When a library is mapped into the address space of a traced process,
ltrace needs to know what the prototypes are of functions that this
library implements. For purposes of ltrace, prototype really is a
bit more than just type signature: it's also formatting of individual
parameters and of return value. These prototypes are stored in files
called prototype libraries.
After a library is mapped, ltrace finds out what its SONAME is. It
then looks for a file named SONAME.conf--e.g. protolib for libc.so.6
would be in a file called libc.so.6.conf. When such file is found
(more about where ltrace looks for these files is below), ltrace
reads all prototypes stored therein. When a symbol table entry point
(such as those traced by -x) is hit, the prototype is looked up in a
prototype library corresponding to the library where the hit
occurred. When a library call (such as those traced by -e and -l) is
hit, the prototype is looked up in all prototype libraries loaded for
given process. That is necessary, because a library call is traced
in a PLT table of a caller library, but the prototype is described at
If a library has no SONAME, basename of library file is considered
instead. For the main program binary, basename is considered as well
(e.g. protolib for /bin/echo would be called echo.conf). If a name
corresponding to soname (e.g. libc.so.6.conf) is not found, and the
module under consideration is a shared library, ltrace also tries
partial matches. Ltrace snips one period after another, retrying the
search, until either a protolib is found, or X.so is all that's left.
Thus libc.so.conf would be considered, but libc.conf not.
When looking for a prototype library, ltrace potentially looks into
several directories. On Linux, those are $XDG_CONFIG_HOME/ltrace,
$HOME/.ltrace, X/ltrace for each X in $XDG_CONFIG_DIRS and
/usr/share/ltrace. If the environment variable XDG_CONFIG_HOME is
not defined, ltrace looks into $HOME/.config/ltrace instead.
There's also a mechanism for loading legacy config files. If
$HOME/.ltrace.conf exists it is imported to every loaded prototype
library. Similarly for /etc/ltrace.conf. If both exist, both are
imported, and $HOME/.ltrace.conf is consulted before
If -F contains any directories, those are searched in precedence to
the above system directories, in the same order in which they are
mentioned in -F. Any files passed in -F are imported similarly to
above legacy config files, before them.
See ltrace.conf(5) for details on the syntax of ltrace prototype
It has most of the bugs stated in strace(1).
It only works on Linux and in some 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)
program if you are under the Debian GNU/Linux distribution.
This page is part of the ltrace (library call tracer) project.
Information about the project can be found at ⟨http://ltrace.org/⟩.
If you have a bug report for this manual page, see
⟨http://ltrace.org/⟩. This page was obtained from the project's
upstream Git repository
⟨git://anonscm.debian.org/collab-maint/ltrace.git⟩ on 2017-03-13. If
you discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for the
page, or you have corrections or improvements to the information in
this COLOPHON (which is not part of the original manual page), send a
mail to email@example.com
January 2013 LTRACE(1)