> /etc/init.d/whatever were all shell scripts, and they all had to implement all the features themselves.

A minimal SystemD service file and a minimal OpenRC service file are equally complex.

Here's the OpenRC service file for ntpd (which is not a minimal service file, but is pretty close):

  #!/sbin/openrc-run
  
  description="ntpd - the network time protocol daemon"
  pidfile="/var/run/ntpd.pid"
  command="/usr/sbin/ntpd"
  command_args="${NTPD_OPTS}"
  command_args_background="-p ${pidfile}"
  command_args_foreground="-n"
  
  depend() {
   use net dns logger
   after ntp-client
  }
  
  start_pre() {
   if [ ! -f /etc/ntp.conf ] ; then
    eerror "Please create /etc/ntp.conf"
    return 1
   fi
   return 0
  }

'depend' handles service dependency declaration and start/stop ordering (obviously).

'start_pre' is a sanity check that could be removed, or reduced to calling an external script (just like -IIRC- systemd forces you to do). There are _pre and _post hooks for both start and stop.

For a service that has no dependencies on other services, backgrounds itself, and creates a pidfile automatically, the smallest OpenRC service file is four non-blank lines: the '#!/sbin/openrc-run' shebang followed by lines declaring 'pidfile', 'command', and 'command_args'. A program that runs only in the foreground adds one more line, which tells OpenRC to handle daemonizing the thing and writing its pidfile: 'command_background="true"'. See [3] for an example of one such service file.

If you want service supervision, it's as simple as adding 'supervisor=supervise-daemon', and ensuring that your program starts in the foreground. If it doesn't foreground itself automatically, then adding 'command_args_foreground=<Program Foregrounding Args>' will do the trick.

If you're interested in more information about OpenRC service file syntax, check out the guide for them at [0], and for a lot more information, the manual for openrc-run at [1]. For supervision, check out the supervision guide at [2].

[0] <https://github.com/OpenRC/openrc/blob/master/service-script-...>

[1] <https://man.uex.se/8/openrc-run>

[2] <https://github.com/OpenRC/openrc/blob/master/supervise-daemo...>

[3] The OpenRC service file for the 'cups-browsed' service (which is a program that does not daemonize itself) is this:

  #!/sbin/openrc-run
  
  pidfile="/run/cups-browsed.pid"
  command="/usr/sbin/cups-browsed"
  command_background="true"
  
  depend() {
   need cupsd avahi-daemon
  }