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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.

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4 Answers 4

up vote 2 down vote accepted

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.

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there's also zram-config in precise now. –  turbo Mar 16 '12 at 13:48
Why was it removed from Raring 13.04? –  NoBugs May 20 '13 at 0:54
The PPA probably hasn't been updated. –  Ryan Thompson May 20 '13 at 18:55

I was struggling with the same problem.

Today I found an excellent blog post about it.

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

Try it.

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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 '11 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. –  Ryan Thompson Mar 16 '12 at 20:17

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
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for i in /dev/ramzswap*;do ... would the better solution I think. Still a tad too hackish in my book. –  turbo Aug 14 '11 at 19:49

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 <>
# 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


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