EDIT: In precise there's now zram-config. It's an upstart job compressing up to half of your ram spread over $(number of CPU cores) swap devices. It didn't allways start at boot but issuing sudo service zram-config start works.

I enabled compcache="256 M" in /etc/initramfs-tools/initramfs.conf as described here (by me :P). This - I believe - creates /dev/ramzswap0 but it is never enabled as swap. It works only after mkswap && swapon.

Then there is the module zram that creates /dev/zram. Is it something else? It works the same way but /dev/ramzswap is created from the module ramzswap.

At the end of the day I wanna have a compressed swap in ram and use the better of the two and for that I need to know how to enable it permanently in a non hackish way. How is this done?

I wrote about ramzswap in Lucid here but things have changed in Natty. You can still enable ramzswap in initramfs.conf but it doesn't get activated.

P.S.:I scanned all udev rules in /lib and/etc but found nothing of interest.

4 Answers 4


There's now a PPA that installs a proper Upstart script for enabling zram at boot-time. It chooses the correct size and number of compressed swap devices for your system.


  • 2
    there's also zram-config in precise now.
    – turbo
    Mar 16, 2012 at 13:48
  • Why was it removed from Raring 13.04?
    – NoBugs
    May 20, 2013 at 0:54
  • The PPA probably hasn't been updated. May 20, 2013 at 18:55

I was struggling with the same problem.

Today I found an excellent blog post about it. http://weirdfellow.wordpress.com/2011/05/04/compressed-ram-with-zram/

Although "sudo start zramswap" didn't work, when I restarted my PC it solved my problem perfectly.

Try it.

  • That's actually the first time I even noticed that there is /etc/init/. Normally I use /etc/init.d/ for starting stuff at boot. Fascinating...
    – turbo
    Sep 6, 2011 at 8:10
  • /etc/init/ is where Upstart init scripts live. The ones in /etc/init.d are mostly just compatibility wrappers that call the ones in /etc/init. Mar 16, 2012 at 20:17

Straight from the Debian wiki. For me, this is the easiest.

First, copy and paste this code into /etc/init.d/zram

# Provides:          zram
# Required-Start:    $local_fs
# Required-Stop:     $local_fs
# Default-Start:     S
# Default-Stop:      0 1 6
# Short-Description: Use compressed RAM as in-memory swap
# Description:       Use compressed RAM as in-memory swap

# Author: Antonio Galea <[email protected]>
# Thanks to Przemysław Tomczyk for suggesting swapoff parallelization


MEMORY=`perl -ne'/^MemTotal:\s+(\d+)/ && print $1*1024;' < /proc/meminfo`
CPUS=`grep -c processor /proc/cpuinfo`

case "$1" in
    param=`modinfo zram|grep num_devices|cut -f2 -d:|tr -d ' '`
    modprobe zram $param=$CPUS
    for n in `seq $CPUS`; do
      i=$((n - 1))
      echo $SIZE > /sys/block/zram$i/disksize
      mkswap /dev/zram$i
      swapon /dev/zram$i -p 10
    for n in `seq $CPUS`; do
      i=$((n - 1))
      swapoff /dev/zram$i && echo "disabled disk $n of $CPUS" &
    sleep .5
    modprobe -r zram
    echo "Usage: `basename $0` (start | stop)"
    exit 1

Next, execute these two commands:

sudo chmod +x /etc/init.d/zram
sudo /etc/init.d/zram start

Finally, to add zram at startup:

sudo update-rc.d zram defaults



Here's the cheap solution. Add the following line to /etc/rc.local, before the exit 0:

find /dev/ -maxdepth 1 -name 'ramzswap*' | while read dev; do
    mkswap $dev
    swapon -p 1000 $dev
  • for i in /dev/ramzswap*;do ... would the better solution I think. Still a tad too hackish in my book.
    – turbo
    Aug 14, 2011 at 19:49
  • How about find /dev/ -maxdepth 1 -name 'ramzswap*' -print0 | while read -d0 dev; do ... ? It'll obviate the problem of strange filename with newline in it.
    – Cbhihe
    Aug 28, 2016 at 14:24
  • @turbo: old stuff here, but I believe Ryan's answer above is actually more general and safer from a scripting viewpoint than what you propose in yr comment. Generally speaking, yr for loop might cause trouble for file names with space and or special characters. This being said you do spare your system a process.
    – Cbhihe
    Aug 28, 2016 at 14:27

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