07-29-2012
As a rule of thumb swap should be roughly equal to installed memory and at least twice the size of the largest process. It is no longer necessary to make swap twice memory (as was required with early unix). Linux uses swap continuously to optimise memory by swapping pages. If swap is too low, the Operating System will fail to function efficiently and may even stall.
With a rogue cron it is easy to exceed the kernel maximum number of files open by one user. If it is a root cron you are heading for a crash.
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LEARN ABOUT REDHAT
swapoff
SWAPON(8) Linux Programmer's Manual SWAPON(8)
NAME
swapon, swapoff - enable/disable devices and files for paging and swapping
SYNOPSIS
/sbin/swapon [-h -V]
/sbin/swapon -a [-v] [-e]
/sbin/swapon [-v] [-p priority] specialfile ...
/sbin/swapon [-s]
/sbin/swapoff [-h -V]
/sbin/swapoff -a
/sbin/swapoff specialfile ...
DESCRIPTION
Swapon is used to specify devices on which paging and swapping are to take place. Calls to swapon normally occur in the system multi-user
initialization file /etc/rc making all swap devices available, so that the paging and swapping activity is interleaved across several
devices and files.
Normally, the first form is used:
-h Provide help
-V Display version
-s Display swap usage summary by device. Equivalent to "cat /proc/swaps". Not available before Linux 2.1.25.
-a All devices marked as ``swap'' swap devices in /etc/fstab are made available. Devices that are already running as swap are silently
skipped.
-e When -a is used with swapon, -e makes swapon silently skip devices that do not exist.
-p priority
Specify priority for swapon. This option is only available if swapon was compiled under and is used under a 1.3.2 or later kernel.
priority is a value between 0 and 32767. See swapon(2) for a full description of swap priorities. Add pri=value to the option field
of /etc/fstab for use with swapon -a.
Swapoff disables swapping on the specified devices and files. When the -a flag is given, swapping is disabled on all known swap devices
and files (as found in /proc/swaps or /etc/fstab).
NOTE
You should not use swapon on a file with holes. Swap over NFS may not work.
SEE ALSO
swapon(2), swapoff(2), fstab(5), init(8), mkswap(8), rc(8), mount(8)
FILES
/dev/hd?? standard paging devices
/dev/sd?? standard (SCSI) paging devices
/etc/fstab ascii filesystem description table
HISTORY
The swapon command appeared in 4.0BSD.
Linux 1.x 25 September 1995 SWAPON(8)