Should init scripts daemonize a process & are pid's essential?

Question

I'm working on getting an init script written for the web-server shiny-server (shiny-server is a version of the R package shiny that allows you to run stand alone web-applications based on R).

I'm working through the Gentoo Handbook : Writing Init Scripts and am reading the Gentoo Developers Guide (as my ultimate aim is to develop an ebuild for installing this on Gentoo, bit of a way to go though).

I had some trouble getting the init script to start so asked on the Shiny Google Group for assistance and one of the developers provided a solution, but at the same time the question arose as to whether Gentoo expects...

a) to have a pid file for each process started.

b) whether it is "best practice" to fork and daemonize a process such as this under Gentoo.

I don't know but am seeking advice to feed back to the developer(s) who seem very open and receptive to getting their software out there and working with distributions.

Currently my init script, which works, looks like....

#!/sbin/runscript
depend(){
    after net
}
start(){
  ebegin "Starting shiny-server"
  start-stop-daemon --start --exec /usr/bin/shiny-server >> /var/log/shiny-server.log 2>&1
  local _retval=$?
  eend "${_retval}"
}
stop(){
  ebegin "Stopping shiny-server"
  start-stop-daemon --start --exec /usr/bin/shiny-server >> /var/log/shiny-server.log 2>&1  
  local _retval=$?
  eend "${_retval}"
}

Thanks in advance for your time,

slackline

Answer 1

Ok, I asked in #gentoo on IRC and was advised by bonsaikitten...

"whatever works best" - start-stop-daemon can create pids too, but I think it's easier to use the function if the process provides it already and daemonized - well, it needs to detach from the current terminal somehow, so either let it do that by itself, or use s-s-d to do it

So I've opted to go with the following to daemonize to background and create PID files...

#!/sbin/runscript

PIDFILE=/var/run/shiny-server.pid

depend(){
    after net
}
start(){
  ebegin "Starting shiny-server"
  start-stop-daemon --start --make-pidfile --pidfile "${PIDFILE}" \
      --background --exec /usr/bin/shiny-server >> /var/log/shiny-server.log 2>&1
  local _retval=$?
  eend "${_retval}"
}
stop(){
  ebegin "Stopping shiny-server"
  start-stop-daemon --stop --pidfile "${PIDFILE}"
  local _retval=$?
  eend "${_retval}"
}

Answer 2

I don't know the best practice used in Gentoo, but i can give you soma e advice how i would handle it on a Debian based system. There exists a file /etc/init.d/skeleton on a Debian/Ubuntu distributions, just google for it. I added the skeleton script below.

Using this skeleton file (it's just a bash script) you will be done in just a couple of minutes.

It uses the start-stop-daemon for handling your program's startup.

That's the way i would do it on a Debian based system. And yes, i recommend to use pid files for every daemon you start.

Hope i could help and good luck!

http://wiki.debian.org/LSBInitScripts

http://www.gentoo.org/doc/en/handbook/handbook-x86.xml?part=2&chap=4

#! /bin/sh
### BEGIN INIT INFO
# Provides:          skeleton
# Required-Start:    $remote_fs $syslog
# Required-Stop:     $remote_fs $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Short-Description: Example initscript
# Description:       This file should be used to construct scripts to be
#                    placed in /etc/init.d.
### END INIT INFO

# Author: Foo Bar <foobar@baz.org>
#
# Please remove the "Author" lines above and replace them
# with your own name if you copy and modify this script.

# Do NOT "set -e"

# PATH should only include /usr/* if it runs after the mountnfs.sh script
PATH=/sbin:/usr/sbin:/bin:/usr/bin
DESC="Description of the service"
NAME=daemonexecutablename
DAEMON=/usr/sbin/$NAME
DAEMON_ARGS="--options args"
PIDFILE=/var/run/$NAME.pid
SCRIPTNAME=/etc/init.d/$NAME

# Exit if the package is not installed
[ -x "$DAEMON" ] || exit 0

# Read configuration variable file if it is present
[ -r /etc/default/$NAME ] && . /etc/default/$NAME

# Load the VERBOSE setting and other rcS variables
. /lib/init/vars.sh

# Define LSB log_* functions.
# Depend on lsb-base (>= 3.2-14) to ensure that this file is present
# and status_of_proc is working.
. /lib/lsb/init-functions

#
# Function that starts the daemon/service
#
do_start()
{
        # Return
        #   0 if daemon has been started
        #   1 if daemon was already running
        #   2 if daemon could not be started
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON --test > /dev/null \
                || return 1
        start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON -- \
                $DAEMON_ARGS \
                || return 2
        # Add code here, if necessary, that waits for the process to be ready
        # to handle requests from services started subsequently which depend
        # on this one.  As a last resort, sleep for some time.
}

#
# Function that stops the daemon/service
#
do_stop()
{
        # Return
        #   0 if daemon has been stopped
        #   1 if daemon was already stopped
        #   2 if daemon could not be stopped
        #   other if a failure occurred
        start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile $PIDFILE --name $NAME
        RETVAL="$?"
        [ "$RETVAL" = 2 ] && return 2
        # Wait for children to finish too if this is a daemon that forks
        # and if the daemon is only ever run from this initscript.
        # If the above conditions are not satisfied then add some other code
        # that waits for the process to drop all resources that could be
        # needed by services started subsequently.  A last resort is to
        # sleep for some time.
        start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec $DAEMON
        [ "$?" = 2 ] && return 2
        # Many daemons don't delete their pidfiles when they exit.
        rm -f $PIDFILE
        return "$RETVAL"
}

#
# Function that sends a SIGHUP to the daemon/service
#
do_reload() {
        #
        # If the daemon can reload its configuration without
        # restarting (for example, when it is sent a SIGHUP),
        # then implement that here.
        #
        start-stop-daemon --stop --signal 1 --quiet --pidfile $PIDFILE --name $NAME
        return 0
}

case "$1" in
  start)
        [ "$VERBOSE" != no ] && log_daemon_msg "Starting $DESC" "$NAME"
        do_start
        case "$?" in
                0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
                2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
        esac
        ;;
  stop)
        [ "$VERBOSE" != no ] && log_daemon_msg "Stopping $DESC" "$NAME"
        do_stop
        case "$?" in
                0|1) [ "$VERBOSE" != no ] && log_end_msg 0 ;;
                2) [ "$VERBOSE" != no ] && log_end_msg 1 ;;
        esac
        ;;
  status)
       status_of_proc "$DAEMON" "$NAME" && exit 0 || exit $?
       ;;
  #reload|force-reload)
        #
        # If do_reload() is not implemented then leave this commented out
        # and leave 'force-reload' as an alias for 'restart'.
        #
        #log_daemon_msg "Reloading $DESC" "$NAME"
        #do_reload
        #log_end_msg $?
        #;;
  restart|force-reload)
        #
        # If the "reload" option is implemented then remove the
        # 'force-reload' alias
        #
        log_daemon_msg "Restarting $DESC" "$NAME"
        do_stop
        case "$?" in
          0|1)
                do_start
                case "$?" in
                        0) log_end_msg 0 ;;
                        1) log_end_msg 1 ;; # Old process is still running
                        *) log_end_msg 1 ;; # Failed to start
                esac
                ;;
          *)
                # Failed to stop
                log_end_msg 1
                ;;
        esac
        ;;
  *)
        #echo "Usage: $SCRIPTNAME {start|stop|restart|reload|force-reload}" >&2
        echo "Usage: $SCRIPTNAME {start|stop|status|restart|force-reload}" >&2
        exit 3
        ;;
esac

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