Add Swap Space on Linux

Find current swap space on the system

# free -m
           total   used    free   shared   buffers  cached
Mem:       16051   15570    481      0       707     12644
-/+ buffers/cache: 2218    13833
Swap:      8189     0      8189

Or

# swapon -s
Filename         Type        Size    Used    Priority
/dev/sda2      partition   8385920    88       -1

 Or

# cat /proc/swaps
Filename         Type        Size    Used    Priority
/dev/sda2      partition   8385920    88       -1

Method 1 - Use Hard Drive Partition

If you have additional hard disk or space available in existing disk then create partition using fdisk command. Assume /dev/sdc1 is newly created partition 

Setup newly created partition as swap area

# mkswap /dev/sdc1

Enable swap partition

# swapon /dev/sdc1

Add following line to /etc/fstab to available even after reboot

# cat /etc/fstab
/dev/sdc1        swap         swap    defaults        0 0

Verify whether newly created swap space is available

# swapon -s
Filename         Type       Size     Used    Priority
/dev/sda2      partition   8385920    88       -1
/dev/sdc1      partition  10234430     0       -2

Method 2 - Use a file for Additional swap space

If you does not have any additional disk then you can create a file on your system and use that for swap space

Create the swap file called 'myswap' using following command (file size in bytes=bs*count)

# dd if=/dev/zero of=/root/myswap bs=1M count=2048

Change the permission of newly created file

# chmod 755 /root/myswap

Make this file as a swap file

# mkswap /root/myswap

Add following line to /etc/fstab to available even after reboot

# cat /etc/fstab
/root/myswap        swap         swap    defaults        0 0

Verify whether newly created swap space is available

# swapon -s
Filename         Type       Size     Used    Priority
/dev/sda2      partition   8385920    88       -1
/root/myswap     file      2097152     0       -2