NAME | SYNOPSIS | DESCRIPTION | OPTIONS | FILTER SPECIFICATIONS | FILTER EXPRESSIONS | PROTOTYPE LIBRARY DISCOVERY | BUGS | FILES | AUTHOR | SEE ALSO | COLOPHON

LTRACE(1)                       User Commands                      LTRACE(1)

NAME         top

       ltrace - A library call tracer

SYNOPSIS         top

       ltrace [-e filter|-L] [-l|--library=library_pattern] [-x filter] [-S]
       [-b|--no-signals] [-i] [-w|--where=nr] [-r|-t|-tt|-ttt] [-T]
       [[-F|--config] pathlist] [-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 filename] [-f] [-p pid] [[--] command [arg ...]]

       ltrace -V|--version

       ltrace -h|--help

DESCRIPTION         top

       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).

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

       -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 received 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
              (i.e. calls done through PLT slots, which are typically calls
              from the main binary to a library, or inter-library calls) to
              trace. Usage examples and the syntax description appear below
              in sections FILTER SPECIFICATIONS and 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, --config 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.  This is as if you specified one -e for
              every symbol implemented in a library specified by
              library_pattern.  Multiple library patters can be specified
              with several instances of this option.  Usage examples and the
              syntax description of library_pattern appear below in sections
              FILTER SPECIFICATIONS and 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 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 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 elfutils or libunwind support was
              enabled at compile time.

       -x filter
              A qualifying expression which modifies which symbol table
              entry points to trace (those are typically calls inside a
              library or main binary, though PLT calls, traced by -e, land
              on entry points as well). Usage examples and the syntax
              description appear below in sections FILTER SPECIFICATIONS and
              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 SPECIFICATIONS         top

       Filters are specified with the -l, -e and -x options. In short they
       mean:

       -x is ´show me what calls these symbols (including local calls)´

       -e is ´show me what calls these symbols (inter-library calls only)´

       -l is ´show me what calls into this library´

       Suppose I have a library defined with this header tstlib.h:

        void func_f_lib(void);
        void func_g_lib(void);

       and this implementation tstlib.c:

        #include "tstlib.h"
        void func_f_lib(void)
        {
            func_g_lib();
        }
        void func_g_lib(void)
        {
        }

       Suppose I have an executable that uses this library defined like this
       tst.c:

        #include "tstlib.h"
        void func_f_main(void)
        {
        }
        void main(void)
        {
            func_f_main();
            func_f_lib();
        }

       If linking without -Bsymbolic, the internal func_g_lib() call uses
       the PLT like external calls, and thus ltrace says:

        $ ltrace -x 'func*' -L ./tst
        func_f_main()                             = <void>
        func_f_lib@tstlib.so( <unfinished ...>
        func_g_lib@tstlib.so()                    = <void>
        <... func_f_lib resumed> )                = <void>
        +++ exited (status 163) +++

        $ ltrace -e 'func*' ./tst
        tst->func_f_lib( <unfinished ...>
        tstlib.so->func_g_lib()                   = <void>
        <... func_f_lib resumed> )                = <void>
        +++ exited (status 163) +++

        $ ltrace -l tstlib.so ./tst
        tst->func_f_lib( <unfinished ...>
        tstlib.so->func_g_lib()                   = <void>
        <... func_f_lib resumed> )                = <void>
        +++ exited (status 163) +++

       By contrast, if linking with -Bsymbolic, then the internal
       func_g_lib() call bypasses the PLT, and ltrace says:

        $ ltrace -x 'func*' -L ./tst
        func_f_main() = <void>
        func_f_lib@tstlib.so( <unfinished ...>
        func_g_lib@tstlib.so()                    = <void>
        <... func_f_lib resumed> )                = <void>
        +++ exited (status 163) +++

        $ ltrace -e 'func*' ./tst
        tst->func_f_lib()                         = <void>
        +++ exited (status 163) +++

        $ ltrace -l tstlib.so ./tst
        tst->func_f_lib()                         = <void>
        +++ exited (status 163) +++

FILTER EXPRESSIONS         top

       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
       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 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.
       Initially, 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         top

       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
       prototype library corresponding to the library where the hit
       occurred.  When a library call (such as those traced by -e and -l) is
       hit, the prototype is looked up in all prototype libraries loaded for
       given process.  That is necessary, because a library call is traced
       in a PLT table 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
       mentioned 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         top

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

       It only works on Linux and in some 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)
       program if you are under the Debian GNU/Linux distribution.

FILES         top

       /etc/ltrace.conf
              System configuration file

       ~/.ltrace.conf
              Personal config file, overrides /etc/ltrace.conf

AUTHOR         top

       Juan Cespedes <cespedes@debian.org>
       Petr Machata <pmachata@redhat.com>

SEE ALSO         top

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

COLOPHON         top

       This page is part of the ltrace (library call tracer) project.
       Information about the project can be found at ⟨http://ltrace.org/⟩.
       If you have a bug report for this manual page, see 
       ⟨http://ltrace.org/⟩.  This page was obtained from the project's
       upstream Git repository 
       ⟨git://anonscm.debian.org/collab-maint/ltrace.git⟩ on 2017-09-15.  If
       you discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for the
       page, or you have corrections or improvements to the information in
       this COLOPHON (which is not part of the original manual page), send a
       mail to man-pages@man7.org

                                January 2013                       LTRACE(1)

Pages that refer to this page: strace(1)ltrace.conf(5)