Storage

lsblk — block devices

A tree of disks, partitions, and logical volumes — size, filesystem, mountpoint.

fdisk and parted — partition a disk

fdisk and parted write a partition table (GPT or MBR) and partitions to a disk; parted -s runs without prompts.

mkfs — create a filesystem

The mkfs command creates an empty ext4 or xfs filesystem on a partition; the old data on it becomes unreachable.

blkid — filesystem UUID, label and type

The blkid command prints the UUID, label and type of the filesystem on a device — what goes into /etc/fstab.

iostat and pidstat — which disk is busy and which process loads it

iostat shows disk load — requests, latency, %util; pidstat shows CPU, memory and disk usage per process.

Mounting and fstab

Mounting filesystems: the mount command, persistent mounts in /etc/fstab, UUIDs and options.

Memory and swap: free, available and the page cache

How to read free: used and free memory, the page cache and available; swap, a swap file and vm.swappiness.

Loop device — a file as a disk

A loop device shows a regular file to the system as a disk: you can partition, format and mount it.

Disk space: df, du, inode

Where the space and inodes went — df, du, finding large files, pitfalls.

Log rotation with logrotate

Keeping logs from filling the disk — rotation, compression, retention, checking configs.

LVM logical volumes

LVM: physical volumes, volume groups and logical volumes (PV → VG → LV), extending and snapshots.

resize2fs / xfs_growfs — growing a filesystem

Grow ext4/xfs after a volume grows — online growth, shrinking only on ext4 offline.

Filesystems: ext4, xfs, fsck

Filesystems: creating one with mkfs, labels and UUIDs, fsck checks, choosing between ext4 and xfs.

NFS network filesystem

Network directories over NFS — exporting on the server, mounting on the client, permissions.

Software RAID with mdadm

Software RAID on Linux — creating an array, checking status, replacing a disk.

qemu-img — virtual machine disk images

Creating and maintaining qcow2 disks — overlays, conversion, resizing.

Disk quotas

Limiting space and file counts per user/group — enabling, configuring, reports.

Docker — containers: running, ports, volumes, networks

Docker runs programs in isolated containers started from images and manages their ports, volumes and networks.

Container images — layers, tags, registries and digests

An image is a read-only stack of layers with files and run settings; Docker creates containers from it.