# phpman > man > ltrace(1) > **TLDR:** Display dynamic library calls of a process. > - Print (trace) library calls of a program binary: `ltrace {{path/to/program}}` - Count library calls. Print a handy summary at the bottom: `ltrace -c {{path/to/program}}` - Trace calls to malloc and free, omit those done by libc: `ltrace -e malloc+free-@libc.so* {{path/to/program}}` - Write to file instead of terminal: `ltrace {{-o|--output}} {{file}} {{path/to/program}}` *Source: tldr-pages* --- [LTRACE(1)](https://www.chedong.com/phpMan.php/man/LTRACE/1/markdown) User Commands [LTRACE(1)](https://www.chedong.com/phpMan.php/man/LTRACE/1/markdown) ## NAME ltrace - A library call tracer ## SYNOPSIS **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 _file__‐ _name_] [-f] [-p _pid_] [[--] _command_ _[arg_ _...]_] **ltrace** -V|--version **ltrace** -h|--help ## DESCRIPTION **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 exe‐ cuted by the program. Its use is very similar to [**strace(1)](https://www.chedong.com/phpMan.php/man/strace/1/markdown)**. ## OPTIONS -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 ("..."). This also limits number of recursive structure expansions. ### -b, --no-signals Disable printing of signals recieved by the traced process. -c 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 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 Trace child processes as they are created by currently traced processes as a result of the [fork(2)](https://www.chedong.com/phpMan.php/man/fork/2/markdown) or [clone(2)](https://www.chedong.com/phpMan.php/man/clone/2/markdown) system calls. The new process is attached immediately. -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)](https://www.chedong.com/phpMan.php/man/ltrace.conf/5/markdown) for details on the syntax of ltrace configuration files. ### -h, --help 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._ Multiple library patters can be specified with several instances of this option. Syn‐ tax of library_pattern is described in section **FILTER** **EXPRESSIONS**. Note that while this option selects calls that might be directed to the selected li‐ braries, 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**. -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 stderr. -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 differ‐ ence between the beginning of successive lines. -s _strsize_ 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 microseconds. -ttt If given thrice, the time printed will include the microseconds and the leading por‐ tion 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. -u _username_ Run command with the userid, groupid and supplementary groups of _username_. This op‐ tion 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 EXPRESSIONS 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+* This reads: trace malloc and free, but don't trace anything that comes from libc. Semi-for‐ mally, the syntax of the above example looks approximately like this: {[+-][_symbol_pattern_][@_library_pattern_]} _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, spe‐ cial 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 consid‐ ered 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 expres‐ sion, 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 ap‐ plying all rules, the symbol is _marked_, it will be traced. ## BUGS It has most of the bugs stated in [**strace(1)](https://www.chedong.com/phpMan.php/man/strace/1/markdown)**. 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 (ltrace-de‐ ), or use the [**reportbug(1)](https://www.chedong.com/phpMan.php/man/reportbug/1/markdown)** program if you are under the Debian GNU/Linux distribution. ## FILES _/etc/ltrace.conf_ System configuration file _~/.ltrace.conf_ Personal config file, overrides _/etc/ltrace.conf_ ## AUTHOR Juan Cespedes <> Petr Machata <> ## SEE ALSO [**ltrace.conf(5)](https://www.chedong.com/phpMan.php/man/ltrace.conf/5/markdown),** [**strace(1)](https://www.chedong.com/phpMan.php/man/strace/1/markdown)**, [**ptrace(2)](https://www.chedong.com/phpMan.php/man/ptrace/2/markdown)** January 2013 [LTRACE(1)](https://www.chedong.com/phpMan.php/man/LTRACE/1/markdown)