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from my linux machine swap is - 0 why , and how to increase the swap?

  [root@my_small_linux free

             total       used       free     shared    buffers     cached

 Mem:       8172212    2087904    6084308          0     270020    1376776

-/+ buffers/cache:     441108    7731104

Swap:            0          0          0
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Why? As it stands this system is a long way from needing any swap. – symcbean Mar 8 '11 at 11:27

2 Answers

up vote 3 down vote accepted

That means, that no swap partition is available. If you have some unused space on hard drive, you can make it a swap partition (via fdisk). Or you can make swap on file. This creates 2GB swap:

dd if=/dev/zero of=/swap bs=1048576 count=2048
mkswap /swap
swapon /swap

And add it to /etc/fstab to be mounted at boot.

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I not get anything by swapon -s ? – klod Mar 8 '11 at 11:18
Okay, you did all 3 commands and swapon -s says nothing? Please send result of ls -lh /swap. That will show how the swap file is created. By the way, you have to do this under root or via sudo. – mkudlacek Mar 8 '11 at 11:24
@Mkudlacek how to build disk partition for swap? – klod Mar 8 '11 at 11:26
As MrShunz showed - via fdisk create partition with id "swap". You can use free space or old unused partition. Then execute mkswap on /dev/sd.. and prepare this partition to be a swap. Turn on the swap via swapon /dev/sd.. and add it /etc/fstab as MrShunz showed. – mkudlacek Mar 8 '11 at 11:31
how to uninstall the swap procedure according to your example – klod Mar 8 '11 at 11:43
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up vote 0 down vote

Could also be that in your /etc/fstab the swap partition is listed by uuid instead of /dev/sd*. If for some reason the uuid changed, it cannot be automatically mounted.

Check with fdisk -l as root/with sudo if it lists some swap partions. My output is:

[snip]

Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           1          34      273073+  83  Linux
/dev/sdb2              35        1340    10490445   83  Linux
/dev/sdb3            1341        1449      875542+  82  Linux swap / Solaris <<--- here it is!
/dev/sdb4            1450        9729    66509100   83  Linux

and then check the symbolik link to UUID with: ls -l /dev/disk/by-uuid/. Im my case:

0 lrwxrwxrwx 1 root root 10 2011-03-08 08:39 3565be89-f1fe-478c-9653-a1dbeb9406a9 -> ../../sdb3

So in /etc/fstab I have:

UUID=3565be89-f1fe-478c-9653-a1dbeb9406a9       none            swap    sw              0       0

Disclaimer: i'm under Ubuntu now, so actual paths might be different under other distros.

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