There are 3 ways to check the current swap usage:
root:~> free -h
total used free shared buff/cache available
Mem: 15G 2.0G 9.1G 300M 4.4G 13G
Swap: 3.8G 0B 3.8G
.
root:~> swapon -s
Filename Type Size Used Priority
/dev/sda2 partition 3999740 0 -1
.
root:~> cat /proc/swaps
Filename Type Size Used Priority
/dev/sda2 partition 3999740 0 -1
If we need more swap space, we can either add a new swap partition or a new swap file. Adding a new swap file tends to be a temporary measure when we can’t use a new partition. We can do it with a sequence of 4 commands:
# dd if=/dev/zero of=/root/swapfile1 bs=1024 count=1024 → create blank 1G file and zero it
# chmod 0600 /root/swapfile1 → set permissions
# mkswap /root/swapfile1 → make it a swap file
# swapon /root/swapfile1 → enable it for use
If we want the swap file to be available after the next reboot then we need to add an entry like the following one to /etc/fstab:
/root/swapfile1 swap swap defaults 0 0
If we want to test the fstab entry, we can do it by switching off and on all swap:
# swapoff -a
# swapon -a
Adding a swap partition is even easier. Once we have the spanky new partition available for use (i.e. /dev/sdh1), we could just execute …