Docker on Debian
================

To enable docker memory limitation, the kernel needs to be loaded with
boot parameters: cgroup_enable=memory swapaccount=1.

This is because enabling memory cgroup support has some run-time overhead,
and kernel maintainers don't want to slow down systems unnecessarily.

http://www.mail-archive.com/debian-bugs-dist@lists.debian.org/msg764104.html
https://github.com/docker/docker/issues/396

To instruct the kernel to enable memory cgroup support, edit
/etc/default/grub and extend GRUB_CMDLINE_LINUX_DEFAULT like:

GRUB_CMDLINE_LINUX_DEFAULT="cgroup_enable=memory swapaccount=1"

Then run update-grub, and reboot.


It's worth pointing out that upstream maintains a "check-config.sh" script for
verifying not only proper kernel configuration (which isn't terribly relevant in
the Debian context), but also the host system configuration, especially and
including whether a properly mounted cgroup hierarchy can be found.  If you're
using cgroupfs-mount or systemd, chances are very high that you have one, but if
not, you're likely to see strange behavior.

In the docker.io package, one can find the "check-config.sh" script under
"/usr/share/docker.io/contrib/check-config.sh", which when run (does NOT require
root/sudo) will report on problems with your installation/configuration.


As noted in the upstream documentation (https://docs.docker.io), Docker will
allow non-root users in the "docker" group to access "docker.sock" and thus
communicate with the daemon.  To add yourself to the "docker" group, use
something like:

adduser YOURUSER docker

As also noted in the upstream documentation, the "docker" group (and any other
means of accessing the Docker API) is root-equivalent.  If you don't trust a
user with root on your box, you shouldn't trust them with Docker either.
If you are interested in further information about the security aspects of
Docker, please be sure to read the "Docker Security" article in the
upstream documentation:

    https://docs.docker.com/engine/security/security/