Hi,
sorry in advance if I'm posting to the wrong list. I need to run systemd
inside a docker container and attach it to the container's stdin/stdout.
The reason for this weird request is the following:
1) I need to use the container for running Gilab CI jobs
2) the software being tested needs systemd to be up and running inside
the container
3) Gitlab CI needs a shell running inside the container and attached to
the container's STDIN/STDOUT
In principle 2) and 3) conflicts because both systemd and the shell
needs to be the ENTRYPOINT of the container: systemd needs to run as PID
1 and the shell needs to be attached to container's STDOUT/STDIN. I have
been able to solve the problem by:
- using /usr/sbin/init as ENTRYPOINT
- enabling a custom unit starting a shell attached to STDOUT/STDIN of PID 1:
[Unit]
Description=Start bash shell attached to container STDIN/STDOUT
[Service]
Type=simple
PassEnvironment=PATH LD_LIBRARY_PATH
ExecStart=/bin/bash -c "exec /bin/bash < /proc/1/fd/0 > /proc/1/fd/1
2>/proc/1/fd/2"
ExecStopPost=/usr/bin/systemctl poweroff
[Install]
WantedBy=multi-user.target
- defining the container=docker environment variable
This works beautifully in a CentOS 7 container running systemd 219:
# ls -l /proc/1/fd
total 0
lr-x------ 1 root root 64 Sep 29 17:39 0 -> pipe:[1308703]
l-wx------ 1 root root 64 Sep 29 17:39 1 -> pipe:[1308704]
l-wx------ 1 root root 64 Sep 29 17:39 2 -> pipe:[1308705]
but fails when running a Ubuntu 20.04 container with systemd 245:
# ls -l /proc/1/fd
total 0
lrwx------ 1 root root 64 Sep 29 17:08 0 -> /dev/null
lrwx------ 1 root root 64 Sep 29 17:08 1 -> /dev/null
lrwx------ 1 root root 64 Sep 29 17:08 2 -> /dev/null
In the latter case the fds of PID 1 are connected to /dev/null, so the
shell is immediately terminated and no Gtilab CI job can be run. The
same behavior occurs with systemd 219 if I don't set container=docker,
but with systemd 245 it happens anyway. It happens anyway also in CentOS
7 when running systemd 234 after updating it as described here:
https://copr.fedorainfracloud.org/coprs/jsynacek/systemd-backports-for-centos-7/
So I believe this problem might have been introduced by a systemd
version subsequent to 219 and that hopefully it might be fixed somehow
by means of e.g. proper configuration of the container/environment, but
I need some advice about what to do since I'm clueless.
Thanks in advance for any help and sorry for the long message,
Nicola
