/etc/init.d/swap-noauto for Linux

swap-noauto

#!/bin/sh

### /etc/init.d/swap-noauto for Linux
### Copyright (C) 2020-2022 by Jim Klimov
### Partially based on https://unix.stackexchange.com/a/594006
### and https://wiki.archlinux.org/index.php/ZFS#Swap_volume

### BEGIN INIT INFO
# Provides:          swap
# Required-Start:    $local_fs
# Required-Stop:     $local_fs
# Default-Start:     2 3 4 5
# Default-Stop:      0 1 6
# Should-Start:
# Should-Stop:
# Short-Description: SWAP (noauto)
# Description: provide "noauto" swap space, okay if not mountable
### END INIT INFO

# EXAMPLE SETUP:
# zfs create -b $(getconf PAGESIZE) \
#          -o logbias=throughput -o sync=always \
#          -o primarycache=metadata \
#          -o com.sun:auto-snapshot=false \
#          -o dedup=off -o checksum=off -o compression=off \
#          -V 8G rpool/swap
# mkswap -f /dev/zvol/rpool/swap
# swapon /dev/zvol/rpool/swap
#
# In /etc/fstab:
#
#   # https://unix.stackexchange.com/a/594006
#   # Swap out tmpfs build workspaces, shared libs and other data, if needed
#   # noauto to avoid congestion if dual-booting to illumos (mkswap needed after)
#   /dev/zvol/rpool/swap none swap discard,noauto 0 0

SWAPDEVS="`grep -w noauto /etc/fstab | grep -w swap | awk '{print $1}' | grep -v '#' | tr '\n' ' '`"
[ -n "$SWAPDEVS" ] || exit 0
(command -v swapon && command -v swapoff) >/dev/null 2>/dev/null || exit 0

# Report to terminal before systemd wraps take over
case $1 in
        status)
                echo "Expected swap devices: $SWAPDEVS"
                swapon -s
                echo "Swap device listing completed"
                ;;
esac

. /lib/lsb/init-functions

case $1 in
        start)
                RES=0
                for S in $SWAPDEVS ; do
                        swapon "$S" || {
                                RES=1
                                echo "FAILED to enable swap on '$S', is it formatted for Linux?" >&2
                        }
                done
                log_end_msg $RES
                ;;
        stop)
                RES=0
                for S in $SWAPDEVS ; do
                        swapoff "$S" || {
                                RES=1
                                echo "FAILED to disable swap on '$S', is it attached and enough memory free?" >&2
                        }
                done
                log_end_msg $RES
                ;;
        reload|restart|force-reload)
                $0 stop
                sleep 1
                $0 start
                ;;
        status)
                echo "Expected swap devices: $SWAPDEVS"
                swapon -s
                echo "Swap device listing completed"
                exit 0
                ;;
        *)
                echo "Usage: /etc/init.d/swap-noauto {start|stop|reload|restart|force-reload|status}"
                exit 1
                ;;
esac

exit 0