Linux storage cheat sheet

The chapter on one page: what to remember, the commands to have at your fingertips, and flashcards for quick revision.

The chapter in eight sentences

Disks and partitions are block devices: sdb is a disk, sdb1 its first partition; lsblk -f and blkid show them with file systems and UUIDs.
A new disk needs four steps: partition (GPT, parted -s), file system (mkfs.xfs, mkfs.ext4, mkswap), mount, and an entry in /etc/fstab.
XFS is the default and can only grow; ext4 can grow and shrink; swap is enabled with swapon, never mounted.
mount DEV DIR, umount DIR, findmnt, df -hT and lsblk -f create and inspect mounts; the mount point must exist.
fstab lines are UUID=… /dir type options 0 0; use UUIDs because device names can change.
Always back up fstab and run systemctl daemon-reload, findmnt --verify and mount -a before rebooting; use nofail for non-essential disks.
"No space left" has three causes: blocks (df -h, du), inodes (df -i) and deleted-but-open files (lsof +L1).
fuser -vm DIR shows what keeps a mount busy; xfs_repair -n and e2fsck -n check unmounted file systems.

Command	Does
`lsblk -f`, `blkid`	Devices, file systems, UUIDs
`parted -s /dev/sdb mklabel gpt`	New GPT table
`parted -s /dev/sdb mkpart NAME xfs 1MiB 1025MiB`	New partition
`mkfs.xfs DEV` · `mkfs.ext4 -L NAME DEV` · `mkswap DEV`	File systems and swap
`mount DEV DIR` · `umount DIR`	Attach / detach
`swapon DEV` · `swapoff DEV` · `swapon --show`	Swap

Item	Detail
Line	`UUID=… /mnt/point xfs defaults 0 0` · swap: `UUID=… none swap defaults 0 0`
Options	`noexec` `nodev` `nosuid` `ro` `nofail`
Safe routine	`cp /etc/fstab /root/fstab.bak` → edit → `systemctl daemon-reload` → `findmnt --verify` → `mount -a` → `swapon -a` → reboot
UUID	`blkid -s UUID -o value DEV`

Command	Does
`df -h` · `df -hT` · `df -i`	Blocks, types, inodes
`du -xh --max-depth=1 DIR \| sort -rh \| head`	Biggest directories
`lsof +L1`	Deleted but open files
`fuser -vm DIR` · `lsof DIR`	Who keeps a mount busy
`xfs_repair -n DEV` · `e2fsck -n DEV`	Check (unmounted)
`xfs_admin -L NAME DEV` · `e2label DEV NAME`	Labels
`xfs_info DIR` · `tune2fs -l DEV`	Details

Four steps for a new disk?: Partition (parted) → file system (mkfs / mkswap) → mount → /etc/fstab.
See disks, partitions, file systems?: lsblk · lsblk -f · blkid · parted -s DISK print
GPT label and a partition?: parted -s /dev/sdb mklabel gpt · parted -s /dev/sdb mkpart NAME xfs 1MiB 1025MiB
Create file systems?: mkfs.xfs DEV · mkfs.ext4 -L LABEL DEV · mkswap DEV
Mount, unmount, show?: mount DEV DIR · umount DIR · findmnt · df -hT
Permanent mount?: UUID=… /dir xfs defaults 0 0 in /etc/fstab; daemon-reload; findmnt --verify; mount -a
Swap?: mkswap DEV · swapon DEV · swapon --show · fstab line with type swap and mount point none
Why UUID?: Device names such as /dev/sdb1 can change; UUIDs do not.
Out of space?: df -h · df -i · du -xh --max-depth=1 DIR | sort -rh · lsof +L1
Busy mount?: fuser -vm DIR · lsof DIR; leave the directory, stop the process
Check a file system?: xfs_repair -n DEV (XFS) · e2fsck -f DEV (ext4), both unmounted
Labels and details?: xfs_admin -L · e2label · xfs_info · tune2fs -l