Infrastructure & Operations › Linux & Servers

Disks, Filesystems and Mounts

Attaching storage and making it usable.

Also known as: mount a filesystem, block device, mount point

A disk (or block device) is a chunk of raw storage — /dev/sda, /dev/nvme0n1. Before you can use it, you put a filesystem on it (ext4, xfs), a structure that turns raw blocks into files and directories. Mounting attaches that filesystem to a directory so it appears in the tree: mount /dev/sdb1 at /data, and files written under /data land on that disk.

lsblk                 # block devices and their mount points
df -h                 # free space per mounted filesystem
mount /dev/sdb1 /data # attach now (until reboot)
umount /data          # detach

To make it permanent, add a line to /etc/fstab (device, mount point, filesystem, options). A typo there can stop the machine from booting, so test with mount -a before rebooting.

The classic mistake is thinking you can just unplug or delete the disk. Unmount first — writing to a filesystem that was pulled out mid-write corrupts it. Two more traps: every mount point shadows whatever was in that directory before, and a full disk breaks services in confusing ways (see disk usage).

On servers, storage is often a logical volume rather than one partition, so you can grow it without repartitioning. In the cloud, you attach a block device, then format and mount it the same way. In Docker and Kubernetes you mount a host path or a persistent volume instead; for the container equivalents see bind mounts vs volumes. Take backups before you shrink or move a filesystem.