You can either use a dedicated hard
drive partition to add new swap space, or create a swap file on an existing
filesystem and use it as swap space.
How
much swap space is currently used by the system?
Free command displays
the swap space. free -k shows the output in KB.
#
free -k
total used free
shared buffers cached
Mem: 3082356 2043700
1038656 0 50976
1646268
-/+
buffers/cache: 346456 2735900
Swap: 4192956 0
4192956
Swapon command with
option -s, displays the current swap space in KB.
#
swapon -s
Filename Type Size Used
Priority
/dev/sda2 partition 4192956 0 -1
Swapon -s, is same as
the following.
#
cat /proc/swaps
Filename Type Size Used
Priority
/dev/sda2 partition 4192956 0 -1
Method
1: Use a Hard Drive Partition for Additional Swap Space
If you have an
additional hard disk, (or space available in an existing disk), create a
partition using fdisk command. Let us assume that this partition is called
/dev/sdc1
Now setup this newly
created partition as swap area using the mkswap command as shown below.
# mkswap /dev/sdc1
Enable the swap
partition for usage using swapon command as shown below.
# swapon /dev/sdc1
To make this swap
space partition available even after the reboot, add the following line to the
/etc/fstab file.
# cat /etc/fstab
/dev/sdc1 swap swap defaults 0 0
Verify whether the
newly created swap area is available for your use.
# swapon -s
Filename Type Size Used
Priority
/dev/sda2 partition 4192956 0 -1
/dev/sdc1 partition 1048568 0 -2
# free -k
total used free
shared buffers cached
Mem: 3082356 3022364
59992 0 52056
2646472
-/+
buffers/cache: 323836
2758520
Swap: 5241524 0
5241524
Note: In the output of swapon -s command, the
Type column will say “partition” if the swap space is created from a disk
partition.
Method
2: Use a File for Additional Swap Space
If you don’t have any
additional disks, you can create a file somewhere on your filesystem, and use
that file for swap space.
The following dd
command example creates a swap file with the name “myswapfile” under /root
directory with a size of 1024MB (1GB).
# dd if=/dev/zero
of=/root/myswapfile bs=1M count=1024
1024+0 records in
1024+0 records out
# ls -l
/root/myswapfile
-rw-r--r-- 1 root
root 1073741824 Aug 14 23:47
/root/myswapfile
Change the permission
of the swap file so that only root can access it.
# chmod 600
/root/myswapfile
Make this file as a
swap file using mkswap command.
# mkswap
/root/myswapfile
Setting up swapspace
version 1, size = 1073737 kB
Enable the newly
created swapfile.
# swapon
/root/myswapfile
To make this swap file
available as a swap area even after the reboot, add the following line to the
/etc/fstab file.
# cat /etc/fstab
/root/myswapfile swap swap defaults 0 0
Verify whether the
newly created swap area is available for your use.
# swapon -s
Filename Type Size Used
Priority
/dev/sda2 partition 4192956 0 -1
/root/myswapfile file 1048568 0 -2
# free -k
total used
free shared buffers
cached
Mem: 3082356 3022364
59992 0 52056
2646472
-/+
buffers/cache: 323836 2758520
Swap: 5241524 0
5241524
Note: In the output of swapon -s command, the
Type column will say “file” if the swap space is created from a swap file.
If you don’t want to
reboot to verify whether the system takes all the swap space mentioned in the
/etc/fstab, you can do the following, which will disable and enable all the
swap partition mentioned in the /etc/fstab
# swapoff -a
# swapon -a
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