swapon Command

The swapon command enables swap space on a device or file, making it available for the kernel's virtual memory system. Swap provides overflow space when physical RAM is full — the kernel moves less-used memory pages to swap, freeing RAM for active processes.

Swap is critical for system stability. Without swap, when RAM is exhausted, the OOM (Out-Of-Memory) killer terminates processes to free memory, which can crash important services. With swap, the system degrades gracefully — slowing down instead of killing processes.

swapon and its counterpart swapoff manage which swap devices and files are active. System administrators use these commands to add swap space on running systems, adjust swap priority, create swap files (preferred over swap partitions on modern systems), and troubleshoot memory pressure situations.

Modern Linux systems often use swap files instead of dedicated swap partitions, as they are easier to resize and manage. Additionally, zram (compressed swap in RAM) and zswap (compressed swap cache) complement traditional swap for better performance.

Option	Description	Example
-s	Display swap usage summary	swapon -s
--show	Show swap devices in columns format	swapon --show
-a	Enable all swaps from /etc/fstab	sudo swapon -a
-p PRIORITY	Set swap priority (higher = used first)	sudo swapon -p 10 /swapfile
DEVICE	Enable swap on a specific device or file	sudo swapon /swapfile
--verbose	Verbose output showing details	sudo swapon --verbose /swapfile