Adding Swap to CentOS 7, RHEL 7, and Oracle Linux 7
1. Check if the System has a Swap partition
# swapon -s
If nothing is returned, then no swap exists.
“free -m” is another way of checking for swap.
# free -m
total used free shared buffers cached
Mem: 2815 393 2421 2 19 124
-/+ buffers/cache: 249 2566
2. Check Storage Space
#df -h
3. Create a Swap File
Example: 4GB swap file called /swap
# fallocate -l 4G /swap
# chmod 600 /swap
# mkswap /swap
4. Verify the Swap file:
# swapon -s
Filename Type Size Used Priority
/swap partition 4194300 0 -1
5. Make the Swap Permanent
Add /swap to /etc/fstab
/swap swap swap sw 0 0
6. Tweak the Swap Settings
Swappiness:
# cat /proc/sys/vm/swappiness
The default value is 30
Set it to 10
# sysctl vm.swappiness=10
To make the swappiness permanent, edit /etc/sysctl.conf and add the setting:
vm.swappiness = 10
Cache Pressure:
# cat /proc/sys/vm/vfs_cache_pressure
The default is 100, which means the system removes the inode info from the cache too quickly, set it to 50
# sysctl vm.vfs_cache_pressure=50
Make the cache pressure setting permanent in /etc/sysctl.conf by adding:
vm.vfs_cache_pressure = 50