Linux Commands Examples

A great documentation place for Linux commands


A library call tracer

see also : strace


ltrace [-CfhiLrStttV] [-a column] [-A maxelts] [-D level] [-e expr] [-l filename] [-n nr] [-o filename] [-p pid] ... [-s strsize] [-u username] [-X extern] [-x extern] ... [--align=column] [--debug=level] [--demangle] [--help] [--indent=nr] [--library=filename] [--output=filename] [--version] [command [arg ...]]

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ltrace ./a.out


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 ("...")


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 level

Show debugging output of ltrace itself. level must be a sum of some of the following numbers:


DEBUG_GENERAL. Shows helpful progress information


DEBUG_EVENT. Shows every event received by a traced program


DEBUG_PROCESS. Shows every action ltrace carries upon a traced process


DEBUG_FUNCTION. Shows every entry to internal functions

-e expr

A qualifying expression which modifies which events to trace. The format of the expression is:
where the values are the functions to trace. Using an exclamation mark negates the set of values. For example -e printf means to trace only the printf library call. By contrast, -e !printf means to trace every library call except printf.

Note that some shells use the exclamation point for history expansion; even inside quoted arguments. If so, you must escape the exclamation point with a backslash.


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.


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.

-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 filename

Display only the symbols included in the library filename. Up to 30 library names can be specified with several instances of this option.


DON’T display library calls (use it with the -S option).

-n, --indent nr

Indent trace output by nr number of spaces for each new nested call. Using this option makes the program flow visualization easy to follow.

-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.


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 epoch.


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.

-X extern

Some architectures need to know where to set a breakpoint that will be hit after the dynamic linker has run. If this flag is used, then the breakpoint is set at extern, which must be an external function. By default, ’_start’ is used. NOTE: this flag is only available on the architectures that need it.

-x extern

Trace the external function extern. This option may be repeated.

-V, --version

Show the version number of ltrace and exit.



System configuration file


Personal config file, overrides /etc/ltrace.conf


It has most of the bugs stated in strace(1).

Manual page and documentation are not very up-to-date.

Option -f sometimes fails to trace some children.

It only works on Linux and in a small subset of architectures.

Only ELF32 binaries are supported.

Calls to dlopen()ed libraries will not be traced.

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

see also

strace , ptrace


Juan Cespedes <cespedes[:at:]debian[:dot:]org>

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