Wednesday, October 30, 2013

How to create an extra swap space using file system

Sometimes you feel constrained due to the the RAM limit of your system especially when you are running heavy duty software’s, in this blog I'll talk about how you can overcome this problem by hav‌ing an extra swap space to give you extra computing power

First of all you can execute swapon command to check how much swap space you already have in your system
$ swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    44732    -1

The above output gives you an indication that you already have a swap space at partition /dev/sda5. The numbers under "Size" and "Used" are in kilobytes. Though I have considerable amount of swap space configured on my system :), let's continue and try to create a new swap using file system. Before starting with creation of swap space let's make sure that I've enough disk space available in my system

$df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda3       448G  123G  303G  29% /
udev            1.9G  4.0K  1.9G   1% /dev
tmpfs           767M   40M  727M   6% /run
none            5.0M     0  5.0M   0% /run/lock
none            1.9G  804K  1.9G   1% /run/shm

So I've a powerful system with 303G of disk space still available, that means I have a liberty of creating a swap space of my liking. I'll user the data dump(dd) command to my supplementary swap file, make sure that you would be running this command using root user.
$dd if=/dev/zero of=/home/sandy/extraswap bs=1M count=512
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 2.41354 s, 222 MB/s

Now we have created a file /home/sandy/extraswap of size 512M which we will be using as a swap partition. Swap can be created by issuing mkswap command
$mkswap /home/sandy/extraswap
Setting up swapspace version 1, size = 524284 KiB
no label, UUID=685ac04a-ad31-48a8-83df-9ffa3dbc6982

Finally we have to run swapon command on our newly created swap partition to bring it into the game
$swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    46248    -1
$swapon /home/sandy/extraswap
$swapon -s
Filename                Type        Size    Used    Priority
/dev/sda5                               partition    8130556    46248    -1
/home/sandy/extraswap                   file        524284    0    -2

As you can notice when we first executed the swapon -s command at that time swap partition was not in the picture, once we executed the command swapon /home/sandy/extraswap  the swap partition was available.

One last thing that we have to do is to add the entry of this swap partition in our /etc/fstab file as with the next system boot the swap partition will not be active by default we have to do the entry of this swap in our /etc/fstab file.