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Man Pages


Manual Reference Pages  -  LTRACE (1)

NAME

ltrace - A library call tracer

CONTENTS

Synopsis
Description
Options
Filter Expressions
Bugs
Files
Author

SYNOPSIS

ltrace [-bCfghiLrStttV] [-a column] [-A maxelts] [-D level] [-e expr] [-l filename] [-n nr] [-o filename] [-p pid] ... [-s strsize] [-u username] [-w count] [-X extern] [-x extern] ... [--align=column] [--debug=level] [--demangle] [--help] [--indent=nr] [--library=filename] [--no-signals] [--output=filename] [--version] [--where=NR] [command [arg ...]]

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 executed 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 ("...")
-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 level
  Show debugging output of ltrace itself. level must be a sum of some of the following numbers:
01 DEBUG_GENERAL. Shows helpful progress information
010 DEBUG_EVENT. Shows every event received by a traced program
020 DEBUG_PROCESS. Shows every action ltrace carries upon a traced process
040 DEBUG_FUNCTION. Shows every entry to internal functions
-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.
-g Do not place breakpoints on PLT entries. This option reduces the output of ltrace. This is commonly used to avoid tracing libc functions.
-F 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.
-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 filename
  Display only the symbols included in the library filename. Up to 30 library names can be specified with several instances of this option.
-L DON’T display library calls (use it with the -S option).
-n, --indent nr
  Indent trace output by nr number of spaces for each new nested call. Using this option makes the program flow visualization easy to follow.
-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.
-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 extern
  Some architectures need to know where to set a breakpoint that will be hit after the dynamic linker has run. If this flag is used, then the breakpoint is set at extern, which must be an external function. By default, ’_start’ is used. NOTE: this flag is only available on the architectures that need it.
-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 a part of 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.

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 symbol matches a + rule, it becomes marked, if it matches a - rule, it becomes unmarked. If, after applying all rules, the symbol is marked, it will be traced.

BUGS

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

Manual page and documentation are not very up-to-date.

Option -f sometimes fails to trace some children.

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) 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@debian.org>
Petr Machata <pmachata@redhat.com>

SEE ALSO

strace(1) , ptrace(2)

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