For example, when I plug in an external hard drive disk enclosure via USB, sometimes the disk is automatically mounted in /media/.

For example, the disk might be mounted to




What are those long IDs?

  • Presumably these are the same identifiers as blkid shows? – Faheem Mitha Aug 6 '14 at 18:59

The longer number is called a Universally Unique Identifier (UUID). It is specified by the filesystem. There is a good Wikipedia article that gives more information on why and how it is used.

FAT filesystems are identified with a shorter ID (the "Volume serial number"). Wikipedia suggests it's actually a timestamp.


It was probably mounted by udisksd. Look in syslog. On my system, inserting a USB stick results in this:

Aug  6 15:17:08 ubuntu udisksd[2856]: Mounted /dev/sdb1 at /media/mp/A88B-3652

udisks tries to provide a unique name for each drive or partition. It searches through all the symlinks that udev creates under /dev/disk. For removable media, it looks at the symlinks in /dev/disk/by-uuid and /dev/disk/by-label. For nonremovable media, it looks in /dev/disk/by-id.

The entries in the by-uuid directory are often, but not always, UUIDs. In your example, the UUID 13f35f59-f023-4d98-b06f-9dfaebefd6c1 was likely generated by a command like mke2fs, which creates filesystems. In the case of my USB stick, A88B-3652 is actually the volume serial number of its fat32 partition.

The entries in the by-label directory are Volume Labels on CD or DVD discs, for example "Ubuntu 14.04 LTS amd64", or filesystem labels created with the -L option to mke2fs or tune2fs.

The entries in the by-id directory are often of the form bustype-manufacturer_device_serialnumber, with a -partn appended for each partition.

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