Contribute: Debugging Asterisk

Precondition

To debug asterisk crashes or freezes, you need the following debug packages on your Wazo Platform (using the 19.14 version as an example):

# wazo-dist wazo-19.14
# apt-get update
# apt-get install gdb libc6-dbg
# apt-get install -t wazo-19.14 asterisk-dbg wazo-libsccp-dbg
# wazo-dist phoenix-buster

So There is a Problem with Asterisk. Now What ?

  1. Find out the time of the incident from the people most likely to know
  2. Determine if there was a segfault
    1. The command grep segfault /var/log/syslog should return a line such as the following:
Oct 16 16:12:43 wazo-1 kernel: [10295061.047120] asterisk[1255]: segfault at e ip b751aa6b sp b5ef14d4 error 4 in libc-2.11.3.so[b74ad000+140000]
2.  Note the exact time of the incident from the segfault line.
3.  Follow the [Debugging Asterisk Crash](#debugging-asterisk-crash)
    procedure.
  1. If you observe some of the following common symptoms, follow the Debugging Asterisk Freeze procedure.
    • The output of command service asterisk status says Asterisk PBX is running.
    • No more calls are distributed and phones go to No Service.
    • Command core show channels returns only headers (no data) right before returning
  2. Fetch Asterisk logs for the day of the crash (make sure file was not already logrotated):
# cp -a /var/log/asterisk/full /var/local/`date +"%Y%m%d"`-`hostname`-asterisk-full.log
  1. Open a new issue on the bugtracker with following information
    • Tracker: Bug
    • Status: New
    • Category: Asterisk
    • In versions: The version of your Wazo installation where the crash/freeze happened
    • Subject : Asterisk Crash or Asterisk Freeze
    • Description : Add as much context as possible, if possible, a scenario that lead to the issue, the date and time of issue, where we can fetch logs and backtrace
    • Attach logs and backtrace (if available) to the ticket (issue must be saved, then edited and files attached to a comment).
    • DO NOT attach the core file publicly! It may contain sensitive information like passwords and should only be shared with people you trust.

Debugging Asterisk Crash

When asterisk crashes, it usually leaves a core file in /var/spool/asterisk/.

You can create a backtrace from a core file named core_file with:

# gdb -batch -ex "bt full" -ex "thread apply all bt" /usr/sbin/asterisk core_file > bt-threads.txt

Debugging Asterisk Freeze

You can create a backtrace of a running asterisk process with:

# gdb -batch -ex "thread apply all bt" /usr/sbin/asterisk $(pidof asterisk) > bt-threads.txt

If your version of asterisk has been compiled with the DEBUG_THREADS flag, you can get more information about locks with:

# asterisk -rx "core show locks" > core-show-locks.txt

Note

Debugging freeze without this information is usually a lot more difficult.

Optionally, other information that can be interesting:

  • the output of asterisk -rx 'core show channels'
  • the verbose log of asterisk just before the freeze

Recompiling Asterisk

It\'s relatively straightforward to recompile the asterisk version of your Wazo with the DEBUG_THREADS and DONT_OPTIMIZE flag, which make debugging an asterisk problem easier.

The steps are:

  1. Uncomment the deb-src line for the Wazo sources:
# sed -i 's/^# *deb-src/deb-src/' /etc/apt/sources.list.d/wazo*
  1. Fetch the asterisk source package:
# mkdir -p ~/ast-rebuild
# cd ~/ast-rebuild
# apt-get update
# apt-get install -y build-essential
# apt-get source asterisk
  1. Install the build dependencies:
# apt-get build-dep -y asterisk
  1. Enable the DEBUG_THREADS and DONT_OPTIMIZE flag:
# cd <asterisk-source-folder>
# vim debian/rules
  1. Update the changelog by appending +debug1 in the package version:
# vim debian/changelog
  1. Rebuild the asterisk binary packages:
# dpkg-buildpackage -us -uc

This will create a couple of .deb files in the parent directory, which you can install via dpkg.

Recompiling a vanilla version of Asterisk

It is sometimes useful to produce a "vanilla" version of Asterisk, i.e. a version of Asterisk that has none of the Wazo patches applied, to make sure that the problem is present in the original upstream code. This is also sometimes necessary before opening a ticket on the Asterisk issue tracker.

Wazo offers a vanilla version of Asterisk, compiled with the DONT_OPTIMIZE flag. This makes filing bug reports to Asterisk much easier.

Note that this version of Asterisk loses some features that are specific to Wazo. The removed features include:

  • Queue skill-based routing
  • Voicemail message consultation via REST API
  • Call transfers via REST API

To install the vanilla version of Asterisk (replace 19.14 with your current version of Wazo):

# wazo-dist wazo-19.14
# apt-get update
# apt-get install -t wazo-19.14 asterisk-vanilla asterisk-vanilla-dbg
# xivo-fix-paths-rights
# wazo-dist phoenix

This command should replace the asterisk package with asterisk-vanilla.

Once the packages are installed, you can reproduce the crash and extract the backtrace logs from the core dump file. Those file may then be used to file a bug report to Asterisk.

To revert this modification, reinstall asterisk (replace 19.14 with your current version of Wazo):

# wazo-dist wazo-19.14
# apt-get update
# apt-get install -t wazo-19.14 asterisk
# xivo-fix-paths-rights
# wazo-dist phoenix

Running Asterisk under Valgrind

  1. Install valgrind:
# apt-get install valgrind
  1. Recompile asterisk with the DONT_OPTIMIZE flag.
  2. Edit /etc/asterisk/modules.conf so that asterisk doesn\'t load unnecessary modules. This step is optional. It makes asterisk start (noticeably) faster and often makes the output of valgrind easier to analyze, since there\'s less noise.
  3. Edit /etc/asterisk/asterisk.conf and comment the highpriority option. This step is optional.
  4. Stop monit and asterisk:
# monit quit
# service asterisk stop
  1. Stop all unneeded Wazo services. For example, it can be useful to stop wazo-calld, so that it won\'t interact with asterisk via the AMI.
  2. Copy the valgrind.supp file into /tmp. The valgrind.supp file is located in the contrib directory of the asterisk source code.
  3. Execute valgrind in the /tmp directory:
# cd /tmp
# valgrind --leak-check=full --log-file=valgrind.txt --suppressions=valgrind.supp --vgdb=no asterisk -G asterisk -U asterisk -fnc

Note that when you terminate asterisk with Control-C, asterisk does not unload the modules before exiting. What this means is that you might have lots of "possibly lost" memory errors due to that. If you already know which modules is responsible for the memory leak/bug, you should explicitly unload it before terminating asterisk.

Running asterisk under valgrind takes a lots of extra memory, so make sure you have enough RAM.

External links