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
       pathlist] [-A maxelts] [-s strsize] [-C|--demangle] [-a|--align column] [-n|--indent nr] [-o|--output filename] [-D|--debug mask] [-u user-
       name] [-f] [-p pid] [[--] command [arg ...]]

       ltrace -c [-e filter|-L] [-l|--library=library_pattern] [-x filter] [-S] [-o|--output filename] [-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).

       ltrace  shows  parameters of invoked functions and system calls.  To determine what arguments each function has, it needs external declara-
       tion 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.

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 recur-
	      sive 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 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 messages.

       -e filter
	      A qualifying expression which modifies which library calls to trace.  The format of the filter expression is described in  the  sec-
	      tion  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 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 LIBRARY DISCOVERY).  If it refers to a file, that file is imported implicitly to all  loaded
	      prototype libraries.

       -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.  Syntax of library_pattern is described in section 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 traced.

       -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 fol-
	      low.  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 exe-
	      cute.  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 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 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.

       -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.

       -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-@libc.so*

       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][@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, 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 short-
       hand, 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  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.   Ini-
       tially,	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 traced.

PROTOTYPE LIBRARY DISCOVERY

       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 proto-
       type  library corresponding to the library where the hit occured.  When a library call (such as those traced by -e and -l) is hit, the pro-
       totype is looked up in all prototype libraries loaded for given process.  That is necessary, because a library call is traced in a PLT  ta-
       ble of a caller library, but the prototype is described at callee library.

       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 /etc/ltrace.conf.

       If  -F contains any directories, those are searched in precedence to the above system directories, in the same order in which they are men-
       tioned 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 library files.

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-devel@lists.alioth.debian.org), or use the reportbug(1)  pro-
       gram 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@debian.org>
       Petr Machata <pmachata@redhat.com>

SEE ALSO

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

								   January 2013 							 LTRACE(1)