Device and Filesystem Identification and Configuration Files

device and filesystem Most devices are indicated by a filename (of a block special device), like /dev/sda1, but there are other possibilities. For example, in the case of an NFS mount, device may look like knuth.cwi.nl:/dir. The device names of disk partitions are unstable; hardware reconfiguration, and adding or removing a device can cause changes in names. This is the reason why it’s strongly recommended to use filesystem or partition identifiers like UUID or LABEL. Currently supported identifiers (tags): LABEL=label Human readable filesystem identifier. See also -L. UUID=uuid Filesystem universally unique identifier. The format of the UUID is usually a series of hex digits separated by hyphens. See also -U. Note that mount uses UUIDs as strings. The UUIDs from the command line or from fstab(5) are not converted to internal binary representation. The string representation of the UUID should be based on lower case characters. PARTLABEL=label Human readable partition identifier. This identifier is independent on filesystem and does not change by mkfs or mkswap operations. It’s supported for example for GUID Partition Tables (GPT). PARTUUID=uuid Partition universally unique identifier. This identifier is independent on filesystem and does not change by mkfs or mkswap operations. It’s supported for example for GUID Partition Tables (GPT). ID=id Hardware block device ID as generated by udevd. This identifier is usually based on WWN (unique storage identifier) and assigned by the hardware manufacturer. See ls /dev/disk/by-id for more details, this directory and running udevd is required. This identifier is not recommended for generic use as the identifier is not strictly defined and it depends on udev, udev rules and hardware. The command lsblk --fs provides an overview of filesystems, LABELs and UUIDs on available block devices. The command blkid -p <device> provides details about a filesystem on the specified device. Don’t forget that there is no guarantee that UUIDs and labels are really unique, especially if you move, share or copy the device. Use lsblk -o +UUID,PARTUUID to verify that the UUIDs are really unique in your system. The recommended setup is to use tags (e.g. UUID=uuid) rather than /dev/disk/by-{label,uuid,id,partuuid,partlabel} udev symlinks in the /etc/fstab file. Tags are more readable, robust and portable. The mount(8) command internally uses udev symlinks, so the use of symlinks in /etc/fstab has no advantage over tags. For more details see libblkid(3). The proc filesystem is not associated with a special device, and when mounting it, an arbitrary keyword - for example, proc - can be used instead of a device specification. (The customary choice none is less fortunate: the error message 'none already mounted' from mount can be confusing.) The files /etc/fstab, /etc/mtab and /proc/mounts The file /etc/fstab (see fstab(5)), may contain lines describing what devices are usually mounted where, using which options. The default location of the fstab(5) file can be overridden with the --fstab path command-line option (see below for more details). The command mount -a [-t type] [-O optlist] (usually given in a bootscript) causes all filesystems mentioned in fstab (of the proper type and/or having or not having the proper options) to be mounted as indicated, except for those whose line contains the noauto keyword. Adding the -F option will make mount fork, so that the filesystems are mounted in

This section discusses how devices and filesystems are identified for mounting, recommending the use of UUIDs and Labels over device names due to their instability. It details various identifiers like LABEL, UUID, PARTLABEL, PARTUUID, and ID, and advises using tags (e.g., UUID=uuid) in /etc/fstab for readability and robustness. It also mentions the files /etc/fstab, /etc/mtab, and /proc/mounts, which store information about mount points and filesystems, and how the `mount -a` command uses /etc/fstab to mount filesystems.