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The phusion/baseimage boasts of taking care of the pid 1 problem with a light weight init process. How can one use the phusion/baseimage properly? I tried to invoke the image with the command ps aux shows ps running with a PID 1.

What did I do wrong? What is the proper way to use the image?

me@host:~/app1$ docker run --rm phusion/baseimage ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 3.0 0.0 29180 1404 ? Rs 01:27 0:00 ps aux

docker has an option --init. That starts init system tini as Pid 1.

tini is stored as /usr/bin/docker-init on host.
Unfortunately, some systems like fedora and openSUSE miss the init binary although --init shows up in docker run --help.

You can add tini to your docker images yourself and define entrypoint with
ENTRYPOINT /tini --. See README for tini.

Further informations about missing /usr/bin/docker-init at: https://github.com/mviereck/x11docker/issues/23#issuecomment-386817295

I figured out (from here) that the proper way to use the phusion/baseimage is to run it as -

docker run --rm -t -i phusion/baseimage /sbin/my_init ps aux`

to have my_init execute as PID1 and have my_init spawn a process for ps aux

*** Running /etc/my_init.d/00_regen_ssh_host_keys.sh...
*** Running /etc/my_init.d/10_syslog-ng.init...
May 8 04:18:23 daf3cfab8573 syslog-ng[10]: syslog-ng starting up; version='3.5.6'
May 8 04:18:23 daf3cfab8573 syslog-ng[10]: WARNING: you are using the pipe driver, underlying file is not a FIFO, it should be used by file(); filename='/dev/stdout'
May 8 04:18:24 daf3cfab8573 syslog-ng[10]: EOF on control channel, closing connection;
*** Running /etc/rc.local...
*** Booting runit daemon...
*** Runit started as PID 16
*** Running ps aux...
May 8 04:18:24 daf3cfab8573 cron[20]: (CRON) INFO (pidfile fd = 3)
May 8 04:18:24 daf3cfab8573 cron[20]: (CRON) INFO (Running @reboot jobs)
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 5.0 0.0 32304 10796 ? Ss+ 04:18 0:00 /usr/bin/python3 -u /sbin/my_init ps aux
root 10 1.0 0.0 72364 7552 ? S 04:18 0:00 /usr/sbin/syslog-ng --pidfile /var/run/syslog-ng.pid -F --no-caps
root 16 0.0 0.0 4392 1124 ? S+ 04:18 0:00 /usr/bin/runsvdir -P /etc/service
root 17 0.0 0.0 37656 3340 ? R+ 04:18 0:00 ps aux
root 18 0.0 0.0 4240 672 ? Ss 04:18 0:00 runsv cron
root 19 0.0 0.0 4240 800 ? Ss 04:18 0:00 runsv sshd
root 20 0.0 0.0 29272 2840 ? S 04:18 0:00 /usr/sbin/cron -f
*** ps exited with status 0.
*** Shutting down runit daemon (PID 16)...
*** Running /etc/my_init.post_shutdown.d/10_syslog-ng.shutdown...
May 8 04:18:24 daf3cfab8573 syslog-ng[10]: syslog-ng shutting down; version='3.5.6'
May 8 04:18:24 daf3cfab8573 syslog-ng[10]: EOF on control channel, closing connection;
*** Killing all processes...