Getting a Backtrace
This document is intended to provide information on how to obtain the backtraces required on the asterisk bug tracker, available at https://github.com/asterisk/asterisk/issues(https://github.com/asterisk/asterisk/issues/).
BLOCKOverview¶
The backtrace information is required by developers to help fix problems with bugs of any kind. Backtraces provide information about what was wrong when a program crashed; in our case, Asterisk.
Preparing Asterisk To Produce Core Files On Crash¶
First of all, when you start Asterisk, you MUST start it with option -g. This tells Asterisk to produce a core file if it crashes.
If you start Asterisk with the safe_asterisk script, it automatically starts using the option -g.
If you're not sure if Asterisk is running with the -g option, type the following command in your shell:
The interesting information is located in the last column.
Second, your copy of Asterisk must have been built without optimization or the backtrace will be (nearly) unusable. This can be done by selecting the 'DONT_OPTIMIZE' option in the Compiler Flags submenu in the 'make menuselect' tree before building Asterisk. Running a production server with DONT_OPTIMIZE is generally safe. You'll notice the binary files may be a bit larger, but in terms of Asterisk performance, impact should be negligible.
Third, your copy of Asterisk must have the debug symbols still included in the binaries. This is the default unless you, or the package maintainer if installing from packages, strips the binaries. Normally a package maintainer will strip the binaries and then provide separate "debug" packages that contain just the symbols. If so, make sure those debug packages are installed.
After Asterisk crashes, a file named "core" will be dumped in the present working directory of the Linux shell from which Asterisk was started or in the location specified by the kernel.core_pattern sysctl setting. In the event that there are multiple core files present, it is important to look at the file timestamps in order to determine which one you really intend to look at.
Getting Preliminary Information After A Crash¶
Before you go further, you must have the GNU Debugger (gdb) installed on the machine that experienced the crash. Use your package manager to install it if it isn't already.
Note
Don't attach core files on the bug tracker as they are only useful on the machine they were generated on. We only need the output of ast_coredumper.
ast_coredumper¶
Asterisk versions 13.14.0, 14.3.0, and later release branches added a few tools to make debugging easier. One of these is ast_coredumper. By default, it's installed in /var/lib/asterisk/scripts and it takes in a core file and produces backtraces and lock dumps in a format for uploading to Jira.
/var/lib/asterisk/scripts/ast_coredumper --help
NAME
ast_coredumper - Dump and/or format asterisk coredump files
SYNOPSIS
ast_coredumper [ --help ] [ --running | --RUNNING ] [ --latest ]
[ --tarball-coredumps ] [ --delete-coredumps-after ]
[ --tarball-results ] [ --delete-results-after ]
[ --tarball-uniqueid="<uniqueid>" ]
[ --no-default-search ] [ --append-coredumps ]
[ <coredump> | <pattern> ... ]
DESCRIPTION
Extracts backtraces and lock tables from Asterisk coredump files.
For each coredump found, 4 new result files are created:
- <coredump>.brief.txt: The output of "thread apply all bt".
- <coredump>.thread1.txt: The output of "thread apply 1 bt full".
- <coredump>.full.txt: The output of "thread apply all bt full".
- <coredump>.locks.txt: If asterisk was compiled with
"DEBUG_THREADS", this file will contain a dump of the locks
table similar to doing a "core show locks" from the asterisk
CLI.
Optional features:
- The running asterisk process can be suspended and dumped.
- The coredumps can be merged into a tarball.
- The coredumps can be deleted after processing.
- The results files can be merged into a tarball.
- The results files can be deleted after processing.
Options:
--help
Print this help.
--running
Create a coredump from the running asterisk instance and
process it along with any other coredumps found (if any).
WARNING: This WILL interrupt call processing. You will be
asked to confirm.
--RUNNING
Same as --running but without the confirmation prompt.
DANGEROUS!!
--latest
Process only the latest coredump from those specified (based
on last-modified time). If a dump of the running process was
requested, it is always included in addition to the latest
from the existing coredumps.
--tarball-coredumps
Creates a gzipped tarball of all coredumps processed.
The tarball name will be:
/tmp/asterisk.<timestamp>.coredumps.tar.gz
--delete-coredumps-after
Deletes all processed coredumps regardless of whether
a tarball was created.
--tarball-results
Creates a gzipped tarball of all result files produced.
The tarball name will be:
/tmp/asterisk.<timestamp>.results.tar.gz
--delete-results-after
Deletes all processed results regardless of whether
a tarball was created. It probably doesn't make sense
to use this option unless you have also specified
--tarball-results.
--tarball-uniqueid="<uniqueid>"
Normally DATEFORMAT is used to make the tarballs unique
but you can use your own unique id in the tarball names
such as the Jira issue id.
--no-default-search
Ignore COREDUMPS from the config files and process only
coredumps listed on the command line (if any) and/or
the running asterisk instance (if requested).
--append-coredumps
Append any coredumps specified on the command line to the
config file specified ones instead of overriding them.
<coredump> | <pattern>
A list of coredumps or coredump search patterns. Unless
--append-coredumps was specified, these entries will override
those specified in the config files.
Any resulting file that isn't actually a coredump is silently
ignored. If your patterns contains spaces be sure to only
quote the portion of the pattern that DOESN'T contain wildcard
expressions. If you quote the whole pattern, it won't be
expanded.
If --no-default-search is specified and no files are specified
on the command line, then the only the running asterisk process
will be dumped (if requested). Otherwise if no files are
specified on the command line the value of COREDUMPS from
ast_debug_tools.conf will be used. Failing that, the following
patterns will be used:
/tmp/core[-._]asterisk!(\*.txt)
/tmp/core[-._]$(hostname)!(\*.txt)
NOTES
You must be root to use ast_coredumper.
The script relies on not only bash, but also recent GNU date and
gdb with python support. \*BSD operating systems may require
installation of the 'coreutils' and 'devel/gdb' packagess and minor
tweaking of the ast_debug_tools.conf file.
Any files output will have ':' characters changed to '-'. This is
to facilitate uploading those files to Jira which doesn't like the
colons.
FILES
/etc/asterisk/ast_debug_tools.conf
~/ast_debug_tools.conf
./ast_debug_tools.conf
#
# This file is used by the Asterisk debug tools.
# Unlike other Asterisk config files, this one is
# "sourced" by bash and must adhere to bash semantics.
#
# A list of coredumps and/or coredump search patterns.
# Bash extended globs are enabled and any resulting files
# that aren't actually coredumps are silently ignored
# so you can be liberal with the globs.
#
# If your patterns contains spaces be sure to only quote
# the portion of the pattern that DOESN'T contain wildcard
# expressions. If you quote the whole pattern, it won't
# be expanded and the glob characters will be treated as
# literals.
#
# The exclusion of files ending ".txt" is just for
# demonstration purposes as non-coredumps will be ignored
# anyway.
COREDUMPS=(/tmp/core[-._]asterisk!(\*.txt) /tmp/core[-._]$(hostname)!(\*.txt))
# Date command for the "running" coredump and tarballs.
# DATEFORMAT will be executed to get the timestamp.
# Don't put quotes around the format string or they'll be
# treated as literal characters. Also be aware of colons
# in the output as you can't upload files with colons in
# the name to Jira.
#
# Unix timestamp
#DATEFORMAT='date +%s.%N'
#
# \*BSD/MacOS doesn't support %N but after installing GNU
# coreutils...
#DATEFORMAT='gdate +%s.%N'
#
# Readable GMT
#DATEFORMAT='date -u +%FT%H-%M-%S%z'
#
# Readable Local time
DATEFORMAT='date +%FT%H-%M-%S%z'
Running ast_coredumper for crashes¶
As you can see, there are lots of options but if the core file is simply named core in your current directory, running /var/lib/asterisk/scripts/ast_coredumper core will usually be sufficient.
Unless you've compiled Asterisk with the DEBUG_THREADS compiler flag (see below), the locks.txt file will be empty.
Many system administrators use the sysctl kernel.core_pattern parameter to control where core files are dumped and what they are named.
You'll notice that the output file names include the full core file name.
If the /etc/asterisk/ast_debug_tools.conf file contained a COREDUMPS entry that would have matched the core file name in /tmp, then you don't even have to supply a path.
By default, ast_coredumper also processes existing core files it detects. You can suppress that using the --no-default-search option and supplying a path directly to a coredump.
Running ast_coredumper for deadlocks, taskprocessor backups, etc.¶
When collecting information about a deadlock or taskprocessor backups, it is useful to have additional information about the threads involved. We can generate this information by attaching to a running Asterisk process and gathering that information. Follow the steps below to collect debug that will be useful to Asterisk developers.
If you can easily reproduce the deadlock, in the Compiler Flags menu of menuselect you should enable DEBUG_THREADS, MALLOC_DEBUG, DONT_OPTIMIZE. Then, you need to recompile, re-install, and restart Asterisk before following the steps below. DEBUG_THREADS is very resource intensive and can seriously impact performance so you should only use it if you can reproduce the issue quickly. Otherwise, DONT_OPTIMIZE is the only option you really need.
When you suspect asterisk is deadlocked or you start seeing "task processor queue reached..." messages, you can use ast_coredumper to dump the currently running asterisk instance.
You can suppress the "continue" prompt by specifying --RUNNING instead of --running.
If Asterisk is truly deadlocked and you compiled with DEBUG_THREADS, the locks.txt file should now contain a table of locks including who's waiting and who's holding.
Reporting crashes and deadlocks¶
Warning
Coredump files may contain sensitive information you might not wish to expose. You should scrub them before attaching them to an issue.
Subject to the warning above, you can attach the text files directly to an Asterisk issue. Occasionally, we'll ask you to run ast_coredumper again with additional options that will create a tarball that includes the Asterisk binaries and the the raw coredump. The command for that is /var/lib/asterisk/scripts/ast_coredumper --tarball-coredumps --no-default-search <path_to_coredump>. We'll give you instructions on how to get the file to us securely.