Coredump file is useful for debuging program crash. This post will show several settings related to coredump.
Enable coredump
If you run program from shell , enable coredump via unlimit -c unlimited， then check unlimit -a | grep core, if it shows unlimited, coredump is enabled for your current session.
If your program is hosted by systemd, you need to edit your program’s service unit file’s [Service] section, add LimitCORE=infinity to enable coredump.
coredump location
Coredump file’s location is determined by kernerl parameter kernel.core_pattern.
On ubuntu 16.04 kernel.core_pattern default value is |/usr/share/apport/apport %p %s %c %P. Leading | means pass coredump file to following program. %p %c %P is used to create dump filename, their meaning can check via man core. apport will save dump file in /var/crash
If your default disk partition don’t have enough space to hold dump file, you can change kernel.core_pattern to another location, eg: /mnt/core/%e-%t.%P. If redis-server crashes, the dump file will be something like /mnt/core/redis-server-1500000000.1452. Also ensure crash process’s running user have write privilege on target location.
systemd-coredump
You can install systemd-coredump to control dump file deeply, like: size, compression….
Its config file is /etc/systemd/coredump.conf.
After install, it will change kernel.core_pattern to |/lib/systemd/systemd-coredump %P %u %g %s %t 9223372036854775808 %e.
By default it will save dump file in /var/lib/systemd/coredump/. But I didn’t find how to modify it to a customize location other than journal log.
After dumped, you can retrive dump file via coredumpctl command.
Trigger process dump core manually.
Send siginal: sudo kill -s SIGSEGV {pid}, it will crash process and save coredump.
Or gcore {pid}, it will make process save core file in current dir, won’t crash it.
Attach coredump file to gdb
Very simple, if the process is redis, and its binary is /usr/local/bin/redis-server, dump file is core. Just gdb /usr/local/bin/redis-server core, needn’t config file. Then you can debug process memory when it crashed.