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9.3. Adding Swap Space

If you are running out of system RAM, you can add virtual memory by using swap space. If you reserved a swap partition on your disk drive, you have to initialize it once using the mkswap command:

# fdisk -l /dev/hda

Disk /dev/hda: 16 heads, 63 sectors, 1575 cylinders
Units = cylinders of 1008 * 512 bytes

   Device Boot    Start       End    Blocks   Id  System
/dev/hda1             1         5      2488+  83  Linux
/dev/hda2             6        10      2520   83  Linux
/dev/hda3            11       141     66024   82  Linux swap
/dev/hda4           142      1575    722736   83  Linux
# mkswap /dev/hda3
Setting up swapspace version 1, size = 67604480 bytes

Then, to activate it, you use the swapon command like this:

# free
             total       used       free     shared    buffers     cached
Mem:         14628      14060        568       8056        100      11664
-/+ buffers/cache:       2296      12332
Swap:            0          0          0
# free
             total       used       free     shared    buffers     cached
Mem:         14628      14060        568       8056        100      11664
-/+ buffers/cache:       2296      12332
Swap:            0          0          0
# swapon /dev/hda3
Adding Swap: 66016k swap-space (priority -2)
# free
             total       used       free     shared    buffers     cached
Mem:         14628      14084        544       8056        100      11648
-/+ buffers/cache:       2336      12292
Swap:        66016          0      66016

If you forgot to reserve (sufficient) space in a separate partition on your disk, you can still use an ordinary file for swap space. You only have to create a file of appropriate size, and initialize it as follows:

# mount /dev/hda4 /mnt
# df
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/root              2087212   1378824    708388  67% /
/dev/hda4               711352        20    675196   1% /mnt
# dd if=/dev/zero of=/mnt/swapfile bs=1024k count=64
64+0 records in
64+0 records out
# mkswap /mnt/swapfile
Setting up swapspace version 1, size = 67104768 bytes

Then activate it:

# free
             total       used       free     shared    buffers     cached
Mem:         14628      14084        544       6200         96      11788
-/+ buffers/cache:       2200      12428
Swap:            0          0          0
# swapon /mnt/swapfile
Adding Swap: 65528k swap-space (priority -3)
# free
             total       used       free     shared    buffers     cached
Mem:         14628      14084        544       6200         96      11752
-/+ buffers/cache:       2236      12392
Swap:        65528          0      65528
9.2. The TMPFS Virtual Memory Filesystem 1. Abstract 9.4. Splash Screen Support in Linux
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