Swap & Disk Usage

Swap

Swap is disk space used as overflow when RAM is full.

$ mkswap /dev/sdb2         # or a file: fallocate -l 2G /swapfile; mkswap /swapfile
$ swapon /dev/sdb2
$ swapon --show
$ free -h                  # see RAM + swap usage

Add to /etc/fstab with swap swap defaults 0 0 for persistence.

Disk Usage

Command	Purpose
`df -h`	Free space per filesystem
`df -i`	Inode usage
`du -sh /var/*`	Size of directories
`ncdu`	Interactive usage browser

Exam trap: A "disk full" error with free space in df -h often means inodes are exhausted - check df -i.