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LTRACE(1)                                   User Commands                                  LTRACE(1)



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).


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) or clone(2) 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) 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+free- AT libc.so*

       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).

       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‐
       vel AT lists.org),  or  use  the  reportbug(1) 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 <cespedes AT debian.org>
       Petr Machata <pmachata AT redhat.com>


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



                                            January 2013                                   LTRACE(1)