Starting ZFS-FUSE up properly

Here is a collection of tips you must pay attention to:

1. Put the ZFS PID file in the root filesystem.
   
2. Unset the LANG environment variable.  Failure to do so will cause ZFS-FUSE to hang if your /usr is on ZFS.
3. Immunize ZFS-FUSE against the OOM killer.  If you don't, then it's very likely that your kernel will kill ZFS-FUSE as soon as things get tight -- and this is something you definitely do not want.
   The listing below contains code to do just that.
   
4. Remove limits.  If you don't remove the limits, ZFS-FUSE will either hang and spin, or consume an inordinate amount of memory (close to two gigabytes).
   

   ulimit -v unlimited
   ulimit -c 512000
   ulimit -l unlimited
   ulimit -s unlimited

For your convenience, I am attaching the script /sbin/zfsctl which I invoke (with the start argument) in /etc/rc.sysinit after mounting other filesystems, and invoke it (with the stop argument) before killall is executed in the S01killall initscript:  It works in Fedora and Ubuntu.

#! /bin/sh

PIDFILE=/.zfs-fuse.pid
LOCKFILE=/var/lock/zfs/zfs_lock

export PATH=/sbin:/bin
unset LANG
ulimit -v unlimited
ulimit -c 512000
ulimit -l unlimited
ulimit -s unlimited

log_action_begin_msg() {
	true # echo $*
}

log_action_end_msg() {
	true # echo $*
}

do_start() {
	test -x /sbin/zfs-fuse || exit 0
	PID=`cat "$PIDFILE" 2> /dev/null`
	if [ "$PID" != "" ]
	then
		if kill -0 $PID 2> /dev/null
		then
			echo "ZFS-FUSE is already running"
			exit 3
		else
			# pid file is stale, we clean up shit
			log_action_begin_msg "Cleaning up stale ZFS-FUSE PID files"
			rm -f "$PIDFILE"
			# /var/run/sendsigs.omit.d/zfs-fuse
			log_action_end_msg 0
		fi
	fi

	log_action_begin_msg "Starting ZFS-FUSE process"
	zfs-fuse -p "$PIDFILE"
	ES_TO_REPORT=$?
	if [ 0 = "$ES_TO_REPORT" ]
	then
		true
	else
		log_action_end_msg 1 "code $ES_TO_REPORT"
		exit 3
	fi

	for a in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
	do
		PID=`cat "$PIDFILE" 2> /dev/null`
		 [ "$PID" != "" ] && break
		sleep 1
	done

	if [ "$PID" = "" ]
	then
		log_action_end_msg 1 "ZFS-FUSE did not start or create $PIDFILE"
		exit 3
	else
		log_action_end_msg 0
	fi

	log_action_begin_msg "Immunizing ZFS-FUSE against OOM kills and sendsigs signals"
	# mkdir -p /var/run/sendsigs.omit.d
	# cp "$PIDFILE" /var/run/sendsigs.omit.d/zfs-fuse
	echo -17 > "/proc/$PID/oom_adj"
	ES_TO_REPORT=$?
	if [ 0 = "$ES_TO_REPORT" ]
	then
		log_action_end_msg 0
	else
		log_action_end_msg 1 "code $ES_TO_REPORT"
		exit 3
	fi
	
	log_action_begin_msg "Mounting ZFS filesystems"
	
	sleep 1
	rm -f /var/lib/random-seed
	zfs mount -a
	ES_TO_REPORT=$?
	if [ 0 = "$ES_TO_REPORT" ]
	then
		log_action_end_msg 0
	else
		log_action_end_msg 1 "code $ES_TO_REPORT"
		#echo "Dropping into a shell for debugging.  Post_mountall pending."
		#bash
		#post_mountall
		exit 3
	fi

	if [ -x /nonexistent -a -x /usr/bin/renice ] ; then # DISABLED
		log_action_begin_msg "Increasing ZFS-FUSE priority"
		/usr/bin/renice -15 -g $PID > /dev/null
		ES_TO_REPORT=$?
		if [ 0 = "$ES_TO_REPORT" ]
		then
			log_action_end_msg 0
		else
			log_action_end_msg 1 "code $ES_TO_REPORT"
			exit 3
		fi
		true
	fi
	
}

do_stop () {
	test -x /sbin/zfs-fuse || exit 0
	PID=`cat "$PIDFILE" 2> /dev/null`
	if [ "$PID" = "" ] ; then
		# no pid file, we exit
		exit 0
	elif kill -0 $PID 2> /dev/null; then
		# pid file and killable, we continue
		true
	else
		# pid file is stale, we clean up shit
		log_action_begin_msg "Cleaning up stale ZFS-FUSE PID files"
		rm -f "$PIDFILE"
		# /var/run/sendsigs.omit.d/zfs-fuse 
		log_action_end_msg 0
		exit 0
	fi

	log_action_begin_msg "Syncing disks"
	sync
	log_action_end_msg 0

	log_action_begin_msg "Unmounting ZFS filesystems"
	zfs unmount -a
	ES_TO_REPORT=$?
	if [ 0 = "$ES_TO_REPORT" ]
	then
		log_action_end_msg 0
	else
		log_action_end_msg 1 "code $ES_TO_REPORT"
		exit 3
	fi
	
	log_action_begin_msg "Terminating ZFS-FUSE process gracefully"
	kill -TERM $PID

	for a in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
	do
		kill -0 $PID 2> /dev/null
		[ "$?" != "0" ] && break
		sleep 1
	done

	if kill -0 $PID 2> /dev/null
	then
		log_action_end_msg 1 "ZFS-FUSE refused to die after 15 seconds"
		exit 3
	else
		rm -f "$PIDFILE"
		# /var/run/sendsigs.omit.d/zfs-fuse 
		log_action_end_msg 0
	fi

	log_action_begin_msg "Syncing disks again"
	sync
	log_action_end_msg 0
}

case "$1" in
  start)
	do_start
	;;
  stop)
	do_stop
	;;
  status)
	PID=`cat "$PIDFILE" 2> /dev/null`
	if [ "$PID" = "" ] ; then
		echo "ZFS-FUSE is not running"
		exit 3
	else
		if kill -0 $PID
		then
			echo "ZFS-FUSE is running, pid $PID"
			zpool status
			exit 0
		else
			echo "ZFS-FUSE died, PID files stale"
			exit 3
		fi
	fi
	;;
  restart|reload|force-reload)
	echo "Error: argument '$1' not supported" >&2
	exit 3
	;;
  *)
	echo "Usage: $0 start|stop|status" >&2
	exit 3
	;;
esac

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