create ramdisk on startup

zram.sh

#!/bin/bash
### BEGIN INIT INFO
# Provides:          zram
# Required-Start:    $all
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:
# Short-Description: your description here
### END INIT INFO
#

# to enable:
# chmod a+x /etc/init.d/zram.sh && systemctl daemon-reload && systemctl enable --now zram

ZRAM_TEMP=/media/local/zram_temp/zram


start() {
   modprobe zram num_devices=3 || ( 
      echo "unable to load zram module, exiting.."
      exit 1
   )

   sleep 3

   [[ -b /dev/zram0 ]] || {
      echo "block device /dev/zram0 does not exist, existing..."
      exit 1
   }

   # compressed
   echo lz4 > /sys/block/zram0/comp_algorithm
   echo 4G > /sys/block/zram0/disksize
   echo 4G > /sys/block/zram0/mem_limit

   # uncompressed
   #echo lzo > /sys/block/zram1/comp_algorithm
   #echo 2G > /sys/block/zram1/disksize
   #echo 2G > /sys/block/zram1/mem_limit


   # for zfs cache
   echo lzo > /sys/block/zram2/comp_algorithm
   echo 2G > /sys/block/zram2/disksize
   echo 2G > /sys/block/zram2/mem_limit




   # yes|mke2fs -q -m 0 -b 4096 -t ext4 -O sparse_super -L zram /dev/zram0
   mkfs.ext4 -F -q -m 0 -b 4096 -t ext4 -O sparse_super -L zram /dev/zram0
   mkdir -p /mnt/zram
   #umount /mnt/zram
   mount -t ext4 -o exec,relatime,nosuid /dev/zram0 /mnt/zram && \
   	[[ -d "$ZRAM_TEMP" ]] && cp -rau "$ZRAM_TEMP"/* /mnt/zram
   
   chmod -R 777 /mnt/zram
   _mount
}

_mount() {
	[[ -d /mnt/zram ]] || exit 0

	apt clean

	mkdir -p /mnt/zram/mount/{cache,tmp}

	cp -rau /var/cache /mnt/zram/mount/
	mount --bind /mnt/zram/mount/cache /var/cache
	mount --bind /mnt/zram/mount/tmp /tmp
}

_umount() {
	umount -l /var/cache
	umount -l /tmp
}

mkdir_zram_temp() {
	 [[ -d "$ZRAM_TEMP" ]] \
	 	&& mkdir -p "$ZRAM_TEMP"/lcx/{proxy,media01/{logs,transcode}} \
	 	&& chmod -R 777 "$ZRAM_TEMP" \
	 	&& echo "zram temp created"
}


stop() {
    timeout 3 umount -l /mnt/zram || true
    _umount
    umount -f /mnt/zram
}

case "$1" in
    start)
       start
       ;;
    stop)
       stop
       ;;
    restart)
       stop
       start
       ;;
    status)
       # code to check status of app comes here
       # example: status program_name
       ;;
    *)
       echo "Usage: $0 {start|stop|status|restart}"
esac

exit 0

# vim /etc/init.d/zram
# chmod a+x /etc/init.d/zram && systemctl daemon-reload && systemctl enable --now zram
# update-rc.d  zram defaults && service zram restart