This is docker-entrypoint.sh intended, as it's name suggests, to run
application(s) in docker container. It can run as container init
process with PID 1 or supervised by another init manager (e.g. PM2
for NodeJS ecosystem).

It's capabilities currently include following:

  1. Delivering signals to the main process it started

  2. Monitor main process and any explicitly declared for such
     supplementary processes, resuming them in cast of SIGSTOP

  3. Terminate main process, it's child processes running in
     same process group and any explicitly declared for
     monitoring supplementary processes

  4. Proxy standard output and error using named pipe optionally
     (e.g. to provide /dev/stdout and /dev/stderr that can be
     (re)opened as regular files to processes it runs; note that
     PM2 provides UNIX domain sockets to processes it runs that
     cannot be (re)opened through /dev/stdout and /dev/stderr)

  5. Proxy syslogd messages from /dev/log and optional
     alternative sockets to standard output with small limitations

It uses job control mechanism provided by most of modern shell
interpreters such as dash(1), mksh(1) and bash(1). Has lightweight
sleep implementation mechanism that does not depend on external
process (e.g. sleep(1) utility) and uses wait(1) for asynchronous
signals processing, which is only command (and builtin) that can
be interrupted at any time. See bash(1) manual page for SIGNALS
section for details on asynchronous signal processing with wait(1).

It is written to be compatible with any shell that supports job
control, however will fallback to bash(1) in case of standard
input is not a TTY because dash(1) job control heavily depends
on it. Other shells may also depend on being a part of controling
TTY foreground process gorup, thus fallback to bash(1) desired.

Project was emerged as part of docker-host project. See it's repo
at https://github.com/serhepopovych/docker-host, especially for
sftp and nginx containers for details on possible usage.