Devices, Linux Filesystems, Filesystem Hierarchy Standard
Devices and Filesystems (plus FHS)
Treat the exam's device, filesystem, and FHS objectives as one study unit, because questions blur them: a partition question quickly becomes a mount and /etc/fstab question.
Devices: block vs character devices, major/minor numbers (ls -l /dev), /dev/sdX naming, and udev. Know blkid, lsblk, fdisk -l (MBR), gdisk/parted (GPT). Scheduling and partition tables: MBR limits (4 primary, 2 TB), GPT advantages.
Filesystems: create with mkfs.ext4, mke2fs -t ext4, mkfs.xfs, mkfs.vfat; inspect with dumpe2fs, tune2fs -l; check/repair with fsck/e2fsck on unmounted filesystems. Mount with mount -t -o; persist in /etc/fstab using UUID (blkid) rather than device names. Know the fields: device, mountpoint, type, options, dump, pass. mount -a tests fstab. Also swapon/swapoff, mkswap, and df/du (blocks used vs directory usage), quota concepts.
FHS: /etc configuration, /var variable data and logs, /usr sharable read-only, /tmp temporary, /opt add-on packages, /proc and /sys virtual filesystems, /boot, /home, /root, /srv, /mnt vs /media, /lib modules and libraries.
Trap: fsck on a mounted read-write filesystem can cause corruption - unmount first. Another: /etc/fstab pass field of 0 means no boot-time check; root is conventionally 1, others 2. Confusing /mnt (admin mounts) with /media (removable) is common.
Worked example: adding a disk - lsblk, fdisk /dev/sdb, mkfs.ext4 /dev/sdb1, add UUID=... /data ext4 defaults 0 2 to fstab, mkdir /data && mount -a.