how to set ulimit / file descriptor on docker container the image tag is phusion/baseimage-docker

Question

I need to set the file descriptor limit correctly on the docker container I connect to container with ssh (https://github.com/phusion/baseimage-docker)

Already tried:

• edit limits.conf the container ignore this file
• upstart procedure found at https://coderwall.com/p/myodcq but this docker image has different kind of init process. (runit)
• I tried to modify configuration of pam library in /etc/pam.d
• try to enabled pam for ssh in sshd_config

The output it always the same.

bash: ulimit: open files: cannot modify limit: Operation not permitted

Answer 1

The latest docker supports setting ulimits through the command line and the API. For instance, docker run takes --ulimit <type>=<soft>:<hard> and there can be as many of these as you like. So, for your nofile, an example would be --ulimit nofile=262144:262144

Answer 2

If using the docker-compose file, Based on docker compose version 2.x We can set like as below, by overriding the default config.

ulimits:
  nproc: 65535
  nofile:
    soft: 26677
    hard: 46677

https://docs.docker.com/compose/compose-file/compose-file-v3/

Answer 3

After some searching I found this on a Google groups discussion:

docker currently inhibits this capability for enhanced safety.

That is because the ulimit settings of the host system apply to the docker container. It is regarded as a security risk that programs running in a container can change the ulimit settings for the host.

The good news is that you have two different solutions to choose from.

1. Remove sys_resource from lxc_template.go and recompile docker. Then you'll be able to set the ulimit as high as you like.

or

2. Stop the docker demon. Change the ulimit settings on the host. Start the docker demon. It now has your revised limits, and its child processes as well.

I applied the second method:

1. sudo service docker stop;

2. changed the limits in /etc/security/limits.conf

3. reboot the machine

4. run my container

5. run ulimit -a in the container to confirm the open files limit has been inherited.

See: https://groups.google.com/forum/#!searchin/docker-user/limits/docker-user/T45Kc9vD804/v8J_N4gLbacJ