General Commands Manual: dphys-swapfile

General Commands Manual: dphys-swapfile


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


       dphys-swapfile setup|swapon|swapoff|uninstall


       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.


              user config

              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
           /sbin/dphys-swapfile setup
           /sbin/dphys-swapfile swapon
           /sbin/dphys-swapfile swapoff
       exit 0

       If an sysadmin wants to  have  his  swapfile  in  annother  place,  say
       /var/run/swap, he can use:

       In /etc/dphys-swapfile:



       [email protected],
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