System information

Tracing Tools 197
17.2 Tracing Library Calls with
ltrace
ltrace traces dynamic library calls of a process. It is used in a similar way to
strace, and most of their parameters have a very similar or identical meaning. By
default, ltrace uses /etc/ltrace.conf or ~/.ltrace.conf configuration
files. You can, however, specify an alternative one with the -F config_file op-
tion.
In addition to library calls, ltrace with the -S option can trace system calls as well:
tux@mercury:~> ltrace -S -o ltrace_find.txt find /etc -name \
xorg.conf; more ltrace_find.txt
SYS_brk(NULL) = 0x00628000
SYS_mmap(0, 4096, 3, 34, 0xffffffff) = 0x7f1327ea1000
SYS_mmap(0, 4096, 3, 34, 0xffffffff) = 0x7f1327ea0000
[...]
fnmatch("xorg.conf", "xorg.conf", 0) = 0
free(0x0062db80) = <void>
__errno_location() = 0x7f1327e5d698
__ctype_get_mb_cur_max(0x7fff25227af0, 8192, 0x62e020, -1, 0) = 6
__ctype_get_mb_cur_max(0x7fff25227af0, 18, 0x7f1327e5d6f0, 0x7fff25227af0,
0x62e031) = 6
__fprintf_chk(0x7f1327821780, 1, 0x420cf7, 0x7fff25227af0, 0x62e031
<unfinished ...>
SYS_fstat(1, 0x7fff25227230) = 0
SYS_mmap(0, 4096, 3, 34, 0xffffffff) = 0x7f1327e72000
SYS_write(1, "/etc/X11/xorg.conf\n", 19) = 19
[...]
You can change the type of traced events with the -e option. The following example
prints library calls related to fnmatch and strlen functions:
tux@mercury:~> ltrace -e fnmatch,strlen find /etc -name xorg.conf
[...]
fnmatch("xorg.conf", "xorg.conf", 0) = 0
strlen("Xresources") = 10
strlen("Xresources") = 10
strlen("Xresources") = 10
fnmatch("xorg.conf", "Xresources", 0) = 1
strlen("xorg.conf.install") = 17
[...]
To display only the symbols included in a specific library, use -l /path/to/li-
brary:
tux@mercury:~> ltrace -l /lib64/librt.so.1 sleep 1