# Ltrace

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Unix programming tool

**ltrace** is a [debugging](/source/Debugging) utility in [Linux](/source/Linux), used to display the calls a [userspace](/source/User_space) application makes to [shared libraries](/source/Library_(computing)#Unix-like_systems).

## Overview

It does this by hooking into the [dynamic loading](/source/Dynamic_loading) system, allowing it to insert [shims](/source/Shim_(computing)) which display the [parameters](/source/Parameter_(computer_programming)) which the applications uses when making the call, and the [return value](/source/Return_statement) which the library call reports. ltrace can also trace Linux [system calls](/source/System_call). Because it uses the dynamic library hooking mechanism, ltrace cannot trace calls to libraries which are [statically linked](/source/Static_library) directly to the target binary. Since 0.7.3, ltrace can also trace calls to libraries which are loaded using [dlopen](/source/Dlopen).

## Example output

The following is the first few lines of an invocation of [xterm](/source/Xterm). It shows ltrace displaying calls to a variety of libraries, including the [C standard library](/source/C_standard_library) ([malloc](/source/Malloc), [strlen](/source/Strlen)), [POSIX libraries](/source/Unistd.h) (getuid), [X Toolkit Intrinsics](/source/X_Toolkit_Intrinsics) (XtOpenApplication), and the [X11 inter-client communication library](/source/X_Window_System_protocols_and_architecture#Inter-client_communication) (IceAddConnectionWatch). A call's return value is shown after the = symbol.

[pid 11783] __libc_start_main(0x407420, 1, 0x7fff75b6aad8, 0x443cc0, 0x443d50 <unfinished ...>
[pid 11783] geteuid()                            = 1000
[pid 11783] getegid()                            = 1000
[pid 11783] getuid()                             = 1000
[pid 11783] getgid()                             = 1000
[pid 11783] setuid(1000)                         = 0
[pid 11783] malloc(91)                           = 0x00cf8010
[pid 11783] XtSetLanguageProc(0, 0, 0, 0x7f968c9a3740, 1) = 0x7f968bc16220
[pid 11783] ioctl(0, 21505, 0x7fff75b6a960)      = 0
[pid 11783] XtSetErrorHandler(0x42bbb0, 0x44f99c, 0x669f80, 146, 0x7fff75b6a72c) = 0
[pid 11783] XtOpenApplication(0x670260, 0x44f99c, 0x669f80, 146, 0x7fff75b6a72c) = 0xd219a0
[pid 11783] IceAddConnectionWatch(0x42adc0, 0, 0, 0x7f968c9a3748, 0 <unfinished ...>
[pid 11783] IceConnectionNumber(0xd17ec0, 0, 1, 0xcfb138, 0xd17c00) = 4
[pid 11783] <... IceAddConnectionWatch resumed> ) = 1
[pid 11783] XtSetErrorHandler(0, 0, 1, 0xcfb138, 0xd17c00) = 0
[pid 11783] XtGetApplicationResources(0xd219a0, 0x6701c0, 0x66b220, 34, 0) = 0
[pid 11783] strlen("off")                        = 3

## See also

- [strace](/source/Strace) – system call tracer for linux

- [ktrace](/source/Ktrace) – system call tracer for *BSD

- [DTrace](/source/DTrace) – Solaris / OS X / BSD / Windows kernel tracing tool

- [SystemTap](/source/SystemTap) – Linux kernel tracing tool

## References

## External links

- [Official website](http://www.ltrace.org)

- [ltrace(1)](https://www.mankier.com/1/ltrace) – [Linux](/source/Linux) General Commands [Manual](/source/Man_page) from ManKier.com

- Rodrigo Rubira Branco, [*Ltrace Internals*](https://www.kernel.org/doc/ols/2007/ols2007v1-pages-41-52.pdf), [Ottawa Linux Symposium](https://web.archive.org/web/20080913185728/http://www.linuxsymposium.org/) 2007

- [latrace](https://latrace.sourceforge.net/latrace.html), a dynamic library call tracer which operates using the LD_AUDIT libc feature

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Adapted from the Wikipedia article [Ltrace](https://en.wikipedia.org/wiki/Ltrace) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Ltrace?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.