Linux swap space - Revision history

Christoph: /* Creating a swap file */

2016-01-14T02:16:33Z

‎Creating a swap file

Christoph: /* Creating a swap file */

2014-11-11T05:43:06Z

‎Creating a swap file

Christoph: /* Creating a swap file */

2014-11-11T05:11:50Z

‎Creating a swap file

Christoph at 20:12, 11 October 2014

2014-10-11T20:12:13Z

Christoph: New page: In Linux, '''swap''' is space on the hard disk that is reserved to be used as virtual memory. ==swappiness== How aggressively your computer uses its swap space is determined by the va...

2013-10-30T04:56:50Z

New page: In Linux, '''swap''' is space on the hard disk that is reserved to be used as virtual memory. ==swappiness== How aggressively your computer uses its swap space is determined by the va...

New page

In [[Linux]], '''swap''' is space on the hard disk that is reserved to be used as virtual memory.

==swappiness==
How aggressively your computer uses its swap space is determined by the value for "swappiness", which is in a range of 0 to 100. A setting of 100 will aggressively move processes, while a setting of 0 will swap only to avoid an out of memory condition.

==Creating a swap file==
As an example, to add 1GB of swap to your computer/server, follow these steps (as superuser/root):

*Create the file to be used for swap:

fallocate -l 1G /mnt/1GB.swap

Or, if <code>fallocate</code> fails or is not installed, run the following command:

dd if=/dev/zero of=/mnt/1GB.swap bs=1024 count=1048576

*Format the file for swap:

mkswap /mnt/1GB.swap

*Add the file to the system as a swap file:

swapon /mnt/1GB.swap

*Add the following line to your <code>/etc/fstab</code> file to make the change permanent:

/mnt/1GB.swap none swap sw 0 0

*To change the swappiness edit <code>/etc/sysctl.conf</code> and add the following line:

vm.swappiness=10

Start with a value of 10 and increase if needed. A typical default value for swappiness is 60. The higher the number, the more often swap is utilized. How much this affects performance depends on how your memory is being used, so experiment to find an optimal value.

*Check that the swap file was created:

sudo swapon -s

Finally, reboot your computer/server to ensure that the changes go into effect.

[[Category:Linux Command Line Tools]]

@@ Line 50: / Line 50: @@
   $ /mnt/1GB.swap  none  swap  defaults  0  0
-*To change the swappiness edit <code>/etc/sysctl.conf</code> and add the following line:
+*To change the swappiness, edit <code>/etc/sysctl.conf</code> (see: [[sysctl]]) and add the following line:
   vm.swappiness=10

@@ Line 58: / Line 58: @@
 *Check that the swap file was created:
-  $ sudo swapon -s
+  $ swapon -s
-Finally, reboot your computer/server to ensure that the changes go into effect.
+Finally, reboot your computer/server to ensure that the changes go into effect. Or, just enable with:
 ==swappiness==

@@ Line 32: / Line 32: @@
 Or, if <code>fallocate</code> fails or is not installed, run the following command:
-  $ dd if=/dev/zero of=/mnt/1GB.swap bs=1024 count=1048576
+  $ dd if=/dev/zero of=/mnt/1GB.swap bs=1024 count=1048576  # echo 1048576/1024^2|bc -l => 1.00
 * Set the right permissions (a world-readable swap file is a huge local vulnerability):

@@ Line 1: / Line 1: @@
 In [[Linux]], '''swap''' is space on the hard disk that is reserved to be used as virtual memory.
-==swappiness==
+==Swap partition==
-How aggressively your computer uses its swap space is determined by the value for "swappiness", which is in a range of 0 to 100. A setting of 100 will aggressively move processes, while a setting of 0 will swap only to avoid an out of memory condition.
 ==Creating a swap file==
@@ Line 9: / Line 28: @@
 *Create the file to be used for swap:
-  fallocate -l 1G /mnt/1GB.swap
+  $ fallocate -l 1G /mnt/1GB.swap
 Or, if <code>fallocate</code> fails or is not installed, run the following command:
-  dd if=/dev/zero of=/mnt/1GB.swap bs=1024 count=1048576
+  $ dd if=/dev/zero of=/mnt/1GB.swap bs=1024 count=1048576
 *Format the file for swap:
-  mkswap /mnt/1GB.swap
+  $ mkswap /mnt/1GB.swap
 *Add the file to the system as a swap file:
-  swapon /mnt/1GB.swap
+  $ swapon /mnt/1GB.swap
 *Add the following line to your <code>/etc/fstab</code> file to make the change permanent:
-  /mnt/1GB.swap  none  swap  sw  0  0
+  $ /mnt/1GB.swap  none  swap  defaults  0  0
 *To change the swappiness edit <code>/etc/sysctl.conf</code> and add the following line:
@@ Line 35: / Line 58: @@
 *Check that the swap file was created:
-  sudo swapon -s
+  $ sudo swapon -s
 Finally, reboot your computer/server to ensure that the changes go into effect.
 [[Category:Linux Command Line Tools]]