ltrace - A library call tracer
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 ...]]
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).
- -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 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.
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.
- /etc/ltrace.conf
- System configuration file
- ~/.ltrace.conf
- Personal config file, overrides /etc/ltrace.conf
Juan Cespedes <cespedes@debian.org>
Petr Machata <pmachata@redhat.com>