dphys-swapfile(8)
NAME
dphys-swapfile - set up, mount/unmount, and delete an swap file
SYNOPSIS
dphys-swapfile setup|install|swapon|swapoff|uninstall
DESCRIPTION
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 deletes it it is not wanted any more.
OPTIONS
There is only one parameter, an command, which can be either of these:
setup and install Both tell 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 changed.
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 we pass up on /etc/fstab, and do our own swapon/off
here.
uninstall
Gets rid of an unwanted swap file, reclaiming its disk space.
CONFIG
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:
CONF_SWAPFILE
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.
CONF_SWAPSIZE
Set size to this absolute value, in MBytes. Leaving this empty
(which is the Default) uses an computed value as size instead.
This is unlikely to ever be needed, unless in some strange
diskspace situations. Note, that swap enabled and size smaller
than RAM may causes kernal-internal VM troubles on some
kernels/systems.
CONF_SWAPFACTOR
Set size to computed value. Uses this value times RAM size. It
so dynamically adapts to RAM size, guarantees enough swap on
large RAM, without going into excess diskspace on small RAM (and
disk?) systems. Defaults to 2, which gives swap size = 2 * RAM
size.
CONF_MAXSWAP
Set size restriction of maximal computed and absolute(!) values,
in MBytes. Defaults to 2048 which was a former 32bit kernel
limit for the swapfile size and is now a limit to prevent
unusually and senselessly big swap files on systems with a lot
of RAM.
FILES
/etc/dphys-swapfile
user config
$CONF_SWAPFILE
the swap file, target of the whole action (defaults to
/var/swap)
EXAMPLES
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:
#!/bin/sh
# /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
start)
/sbin/dphys-swapfile setup
/sbin/dphys-swapfile swapon
;;
stop)
/sbin/dphys-swapfile swapoff
;;
esac
exit 0
If an sysadmin wants to have the swapfile in another place, say
/var/run/swap, he can use:
In /etc/dphys-swapfile:
CONF_SWAPFILE=/var/run/swap
AUTHOR
neil@franklin.ch, http://neil.franklin.ch/
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