dphys-swapfile - set up, mount/unmount, and delete an swap file
dphys-swapfile computes the size for an optimal swap file (and resizes
an existing swap file if necessary), mounts an swap file, unmounts it,
and and delete it if not wanted any more.
There is only one parameter, an command, which can be either of these:
setup Tells dphys-swapfile to compute the optimal swap file size and
(re-)generate an fitting swap file. Default it 2 times RAM size.
This can be called at boot time, so the file allways stays the
right size for current RAM, or run by hand whenever RAM size has
swapon and swapoff These run the swapon and swapoff commands on the
swapfile. Note that direct swapon/off from /etc/fstab is not
possible, as that is (at least on Debian) done in the same
script that mounts /var (which is where the swap file most
likely resides). And we need to do our setup between those
actions. So pass up /etc/fstab, and do our own swapon/off.
Gets rid of an unwanted swap file, reclaiming the disk space.
The config file /etc/dphys-swapfile allows the user to set up the
working environment for dphys-swapfile.
This config file is a sh script fragment full of assignments, which is
sourced. Standard sh syntax rules apply. Assignments are:
Set where the swap file should be placed. Defaults to /var/swap.
It is unlikely that you will need to change this, unless you
have very strange partitioning, and then you will most likely be
using an swap partition anyway.
Force file size to this. Default is 2*RAM size. This is unlikely
to be needed, unless in strange diskspace situations. Note that
swap enabled and smaller than RAM causes kernal-internal VM
trouble on random systems.
Set the relation between RAM and swap size. Must be an integer.
Defaults to 2 which means swap size = 2 * RAM size
Set maximum size of the swap file in MBytes. Defaults to 2048
which was the former kernel limit for the swapfile size and is
now a limit to prevent unusual big swap files on systems with a
lot of RAM.
the swap file, target of the whole action (defaults to
dphys-swapfile is usually run at system startup and shutdown from an
/etc/init.d (or /etc/rc.d) script, such as this (minimal) one:
# /etc/init.d/dphys-swapfile - automatically set up an swapfile
# author franklin, last modification 2004.06.04
# This script is copyright ETH Zuerich Physics Departement,
# use under either modified/non-advertising BSD or GPL license
case "$1" in
If an sysadmin wants to have his swapfile in annother place, say
/var/run/swap, he can use: