Swap Virtual Memory help vps server with little amount of memory to add more amount of memory with Swap partition. For example, upgrade amount of RAM in system from 512 MB to 1 GB by create Swap partition 512 MB. Please note that not all vps hosting provider granted an VPS based on openVZ to create Swap Virtual Memory
Check physical memory usage, see physical memory free left only 34 MB, not good, vps server may stop working
#free -m
total used free shared buffers cached
Mem: 490 455 34 0 24 73
-/+ buffers/cache: 358 131
Swap: 0 0 0
Check disk space availability
#df Filesystem 1K-blocks Used Available Use% Mounted on /dev/vda1 9256088 1475508 7308836 17% / tmpfs 250996 0 250996 0% /dev/shm
Add a swap file:
Determine the size of the new swap file in megabytes and multiply by 1024 to determine the number of blocks. For example, the block size of a 512 MB swap file is 524288.
At a shell prompt as root, type the following command with count being equal to the desired block size: dd if=/dev/zero of=/swapfile bs=1024 count=524288
#dd if=/dev/zero of=/swapfile bs=1024 count=524288 524288+0 records in 524288+0 records out 524288824 bytes (512 MB) copied, 10.192 s, 105 MB/s
#mkswap /swapfile
mkswap: /swapfile: warning: don't erase bootbits sectors
on whole disk. Use -f to force.
Setting up swapspace version 1, size = 524288KiB
no label, UUID=d2592b02-8cb8-4892-8a5a-5af7f9654cc1
#swapon /swapfile
#swapon -s Filename Type Size Used Priority /swapfile file 524288 0 -1
#vi /etc/fstab
# Paste this following line at bottom
/swapfile swap swap defaults 0 0
To prevent the file from being world-readable, you should set up the correct permissions on the swap file:
#chown root:root /swapfile #chmod 0600 /swapfile
Check the result!
#free -m
total used free shared buffers cached
Mem: 490 483 6 0 4 121
-/+ buffers/cache: 357 132
Swap: 511 0 511