Storage Management
Swap memory
Instructions on how to create swap space in RHEL/Fedora systems.
Check swap memory status by using one or more of the following commands:
swapon -s
cat /proc/swaps
free -h
Example output in a system where there was no swap memory set:
[root@almalinux ~]# free -h
total used free shared buff/cache available
Mem: 7.7Gi 417Mi 7.3Gi 16Mi 227Mi 7.3Gi
Swap: 0B 0B 0B
Create an empty file of size 4GB for swap:
dd if=/dev/zero of=/swapfile bs=1M count=4096
Set file permissions:
chmod 0600 /swapfile
Make it swap:
mkswap /swapfile
Activate the swap file immediately:
swapon /swapfile
Now use the first set of commands to check the status of swap memory.
[root@almalinux ~]# free -h
total used free shared buff/cache available
Mem: 7.7Gi 405Mi 3.3Gi 16Mi 4.2Gi 7.3Gi
Swap: 4.0Gi 0B 4.0Gi
Edit the /etc/fstab file with the following entries to enable the swap file at
boot time and make it permanent:
/swapfile none swap defaults 0 0
Optionally, adjust the kernel parameters by adding following to
/etc/sysctl.conf:
vm.swappiness=10
The swappiness value can be in the range [0, 100]. The higher the parameter value, the more aggressively inactive processes are swapped out from physical memory leaving more room for caching. The lower the value, the less they are swapped, forcing filesystem buffers to be emptied. On most systems, vm.swappiness is set to 60 by default. Read more about it here.
Restart daemons:
systemctl daemon-reload