What's runsvdir of Docker container?

Question

I have Docker containers with specific processes, but all of them started with runsvdir.

/usr/bin/containerd-shim-runc-v2 -namespace moby -id ...
 \_ /bin/bash /assets/wrapper
     \_ runsvdir -P /opt/...

Answer 1

runsvdir indicates that these containers are using runit as a service manager. Runit is an init replacement; from the website description:

runit is a cross-platform Unix init scheme with service supervision, a replacement for sysvinit, and other init schemes. It runs on GNU/Linux, *BSD, MacOSX, Solaris, and can easily be adapted to other Unix operating systems. If runit runs for you on any other operating system, please let me know..

The runsvdir program itself is documented here.