Container init process¶

To enable running multiple processes, containers require process/service management. This is normally provided by some kind of init task (e.g. provided by sysvinit).

There are Docker-compatible replacements for full-fledged @init@s. Unfortunately they require either custom init scripts or service configurations. The process of migration from system provided OpenRC init scripts is time consuming and error prone.

• it mostly does not respond to Unix signals, which are used by Docker to manage containers (most importantly: signal termination),
• it does not stop properly on container stop. Attempt to stop container with init as PID 1 ends with error code 137:
  

  CONTAINER ID  IMAGE                 COMMAND       CREATED             STATUS                      PORTS  NAMES
  b755c0f1b1d8  gentoo-base:20220415  "/sbin/init"  About a minute ago  Exited (137) 9 seconds ago         gentoo-base
  

  
  init process remains running afterwards:
  

  # docker-compose top
  gentoo-base
  UID    PID    PPID   C   STIME   TTY     TIME       CMD
  ----------------------------------------------------------
  root   3510   3489   0   17:40   ?     00:00:00   init [0]
  

Nevertheless it is possible to use sysvinit as a Docker container init process. Required steps are following: