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dphys-swapfile

NAME

dphys-swapfile - set up, mount/unmount, and delete an swap file

SYNOPSIS

dphys-swapfile setup|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 and delete it if not wanted any more.

OPTIONS

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 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 pass up /etc/fstab, and do our own swapon/off.

uninstall

Gets rid of an unwanted swap file, reclaiming the 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

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.

CONF_SWAPFACTOR

Set the relation between RAM and swap size. Must be an integer. Defaults to 2 which means swap size = 2 * RAM size

CONF_MAXSWAP

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.

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 his swapfile in annother place, say /var/run/swap, he can use:

In /etc/dphys-swapfile:

CONF_SWAPFILE=/var/run/swap

AUTHOR

franklin@phys.ethz.ch, http://www.phys.ethz.ch/~franklin/