A server's /etc/fstab refers to data partitions as /dev/sdb1 and /dev/sdc1. After an extra disk controller is installed, the machine fails to boot correctly. Why does using UUID= instead avoid this class of failure?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Not correct UUIDs are generated fresh at every boot, so they always match the current device order.
Wrong, and backwards. A UUID is fixed at mkfs time and only changes if you deliberately change it (for ext, tune2fs -U). Its whole value is that it does not change.
Correct A UUID is stored inside the filesystem itself, so it follows the data no matter which /dev/sd* name the kernel assigns during that boot.
Correct. Kernel device names are handed out in detection order, which changes when hardware, drivers or boot timing change. The filesystem UUID is written by mkfs and travels with the filesystem.
Not correct Mounting by UUID skips the filesystem check, so a renamed device cannot stall the boot.
Wrong. The fsck pass field governs checking, and it applies identically whether the entry names a device, a LABEL or a UUID.
Not correct UUIDs are resolved by DNS, so they work even if the local device nodes are missing.
Wrong. Nothing here involves the network. Device UUIDs are resolved locally by udev, which populates /dev/disk/by-uuid/ symlinks.
Why
Persistent naming options in fstab are UUID=, LABEL= and PARTUUID=. Their identifiers live with the filesystem or partition table rather than with the enumeration order, so they survive added disks, changed cabling and different boot timing. `blkid` and `lsblk -f` print them; udev exposes them as symlinks under /dev/disk/.
Where this comes from
- Cited
- LPI exam objective 104.3
- What it says
- Identify filesystems by UUID or label rather than by unstable device names.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 104 and space the ones you get wrong.