How to get core file of segmentation fault process in Docker

Configure to get core file

Run following commands in a start up script of docker container.

echo '/tmp/core.%h.%e.%t' > /proc/sys/kernel/core_pattern
ulimit -c unlimited

• In some case, default value of /proc/sys/kernel/core_pattern is pipe. Then, it should be configured explicitly
• Configure size of core file by ulimit command

Setting for the program

• Enable debug option if the program is compiled by yourself. Install debug symbol if it's from package manager.
• Do not delete source code in docker image.

Run container

• Use --privileged option when docker run to allow write permission for /proc/sys/kernel/core_pattern

After segmentation fault

• Check your container ID by docker ps -a command
• Create docker image from the container by docker commit
  • example) docker commit -m "coredump" 92b8935a7cd7 (92b8935a7cd7 is container ID）
• docker run -it <created image ID> sh and boot a container in a state immediately after segmentation falut

After boot a container

• Install gdb if it hasn't been installed
• Run gdb /path/to/binary /path/to/corefile
• Enjoy debugging

Comments

[Jason Meridth]

Awesome article. Only tip, is if you're using docker-compose you can use privileged: true from docs in your docker-compose.yml file.