This document discusses various debugging tools for Linux systems including ldd, strace, ltrace, and GDB. Ldd displays shared library dependencies, strace and ltrace trace system calls and library functions respectively, and GDB is the GNU debugger that allows setting breakpoints and examining processes. The document encourages writing code as cleverly as possible since debugging is harder than writing code, and provides tips on configuring and using these debugging tools.

1. Debugging toolsDebugging tools
Мариян HackMan Маринов
<mm@1h.com>

3. Кой съм аз?Кой съм аз?
➢ Chief system architect of
➢ Sysadmin since the stone age
➢ The longest course in SoftUni
Linux System Administration

4. What is this talk about?What is this talk about?

5. Debugging is twice as hard as writing the code inDebugging is twice as hard as writing the code in
the first place.the first place.
Therefore, if you write the code AS CLEVERLY ASTherefore, if you write the code AS CLEVERLY AS
POSSIBLE, you are by DEFINITION, not smartPOSSIBLE, you are by DEFINITION, not smart
enough to debug it.enough to debug it.
-- Brian Kernighan-- Brian Kernighan

9. LDDLDD

10. $ ldd
$ ldd -r
$ ldd -v

11. STRACESTRACE

13. stracestrace
-o logfile
-f follow
-s string size
-p PID
-n NUM

14. stracestrace
-e
trace=open (syscall)
trace=file
trace=network
trace=desc

15. LTRACELTRACE

16. Nasty bugsNasty bugs

17. -o logfile
-f follow
-p PID
-n 4
$ ltrace -n 4 sed -v
-l library
{[+-][symbol_pattern][@library_pattern]}

18. GDBGDB

20. GDB ­ GNU debuggerGDB ­ GNU debugger
$ gcc -g$ gcc -g
➢ backtrace (bt)backtrace (bt)
➢ bt with core.dumpbt with core.dump
➢ frameframe
➢ printprint

21. GDB configurationGDB configuration
➢set follow-fork-mode childset follow-fork-mode child
➢parent - do not trace the childparent - do not trace the child
➢child - trace the child alsochild - trace the child also
➢ask - ask the userask - ask the user

22. GDB configurationGDB configuration
Should we stop the trace after exec ?Should we stop the trace after exec ?
➢set follow-exec-mode newset follow-exec-mode new
➢ new - follow the new processnew - follow the new process
➢ same - keep the same processsame - keep the same process

23. GDB configurationGDB configuration
Should we trace the child processes?Should we trace the child processes?
➢set detach-on-fork onset detach-on-fork on
➢ on - detach the child processon - detach the child process
➢ off - do not detachoff - do not detach

24. Въпроси?Въпроси?
Мариян HackMan MarinovМариян HackMan Marinov
E-Mail:E-Mail: mm@1h.commm@1h.com
IRC: irc.freenode.net HackManIRC: irc.freenode.net HackMan
ICQ: 7556201ICQ: 7556201
Jabber/Gtalk:Jabber/Gtalk: hackman@jabber.orghackman@jabber.org
http://github.com/hackman/http://github.com/hackman/