udflabel man page

udflabel — show or change UDF filesystem label


udflabel [encoding-options] [block-options] [identifier-options] device [new-label]


When udflabel is invoked without identifier-options and without specifying new-label then it shows current label of UDF filesystem on device to standard output terminated by new line. Otherwise it updates UDF filesystem (up to the revision 2.60) on device with new specified identifiers from identifier-options. Specifying new-label is synonym for both --lvid and --vid, see section Udf Label and Uuid.


General Options


Display the usage and the list of options.

Block Options

-b,--blocksize= block-size

Specify the size of blocks in bytes. Valid block size for a UDF filesystem is a power of two in the range from 512 to 32768 and must match a device logical (sector) size. If omitted, udflabel tries to autodetect block size. First it tries logical (sector) size and then all valid block sizes.

--vatblock= vat-block

Specify the block location of the Virtual Allocation Table. Virtual Allocation Table is present only on UDF disks with Virtual Partition Map and must be at the last written/recorded disk block.

If omitted, udflabel for optical disc tries to detect the last recorded block with fallback to the last block of block device or disk file image. In most cases, this fallback does not have to work and for disk file images with Virtual Allocation Table it is necessary to specify the correct location.

Virtual Allocation Table contains Logical Volume Identifier (UDF Label).


Force updating UDF disks without write support. Some media, like CD-ROM, DVD-ROM or BD-ROM are read-only. Other media, like CD-RW or DVD-RW, are write-once. UDF is designed also for such media where updating Label or Identifiers is not possible. But in some rare cases, it could make sense to try and overwrite the existing Label or Identifiers also for UDF filesystem which has Access Type either Read-Only or Recordable (Write-Once). This is possible only if underlying media supports overwriting. E.g. UDF image of CD-ROM stored on hard disk or Read-Only UDF image burned to DVD-RAM or BD-RE discs. Option --force ignores UDF Access Type and treats it as Overwritable.


Not really, do not write to device. Just simulate and display what would happen with device. Useful for determining which UDF blocks would be overwritten.

Identifier Options

-u,--uuid= uuid

Specify the UDF uuid. Must be exactly 16 hexadecimal lowercase digits and is used for first 16 characters of --fullvsid option. Special value random generates new uuid from local time and a random number. See section Udf Label and Uuid.

--lvid= new-logical-volume-identifier

Specify the new Logical Volume Identifier.

--vid= new-volume-identifier

Specify the new Volume Identifier.

--vsid= new-volume-set-identifier

Specify the new 17.–127. character of Volume Set Identifier. See section Udf Label and Uuid.

--fsid= new-file-set-identifier

Specify the new File Set Identifier.

--fullvsid= new-full-volume-set-identifier

Specify the new Volume Set identifier. Overwrite previous --uuid and --vsid options. See section Udf Label and Uuid.

Encoding Options


Treat identifier string options as strings encoded according to current locale settings (default). Must be specified as the first argument.


Treat identifier string options as strings encoded in 8-bit OSTA Compressed Unicode format, equivalent to Latin1 (ISO-8859-1). Must be specified as first argument.


Treat identifier string options as strings encoded in 16-bit OSTA Compressed Unicode format, equivalent to UCS-2BE. Note that it is not possible to include zero byte in command line options, therefore any character which has at least one zero byte cannot be supplied (this applies to all Latin1 characters). Must be specified as the first argument.


Treat identifier string options as strings encoded in UTF-8. Must be specified as the first argument.

Udf Label and Uuid

UDF specification does not say anything about a disk label but it describes that UDF Logical Volume Identifier is an extremely important field for media identification in a jukebox as that field is displayed to the user. And based on this statement it is a common practice for the majority of UDF implementations to use UDF Logical Volume Identifier as a UDF disk label.

UDF specification does not have a concept of disk UUID like other filesystems. But mandates that the first 16 characters of UDF Volume Set Identifier are unique, a non-fixed and a non-trivial value. Plus first eight characters are hexadecimal digits. Windows application format.exe and Mac OS X application newfs_udf are known to violates this requirement and set only the first 8 characters as unique (others are fixed). Since, there are still a lot of UDF implementations which use in the first 16 characters only hexadecimal digits and all compliant UDF implementations have hexadecimal digits in the first 8 characters, the following algorithm for generating stable UUID was informally chosen and now is used by udftools, util-linux, grub2 and other projects:

0. If Volume Set Identifier has less then 8 characters then stop with empty UUID
1. Take the first 16 bytes from UTF-8 encoded string of Volume Set Identifier
2. If all bytes are hexadecimal digits then use their lowercase form as UUID
3. If first 8 bytes are not all hexadecimal digits then convert those 8 bytes to their hexadecimal representation (resulting in 16 bytes) and use as UUID
4. Otherwise, compose UUID from two 8 byte parts:

1. part: Use the lowercase form of the first 8 bytes (which are hexadecimal digits)
2. part: Convert next 4 bytes (9.–12. pos.) to their hexadecimal representation

Which means that this generated UUID has always 16 hexadecimal lowercase digits. In most cases, this UUID matches case-insensitively the first 16 characters of UDF Volume Set Identifier and for all disks compliant to the UDF specification the first 8 bytes of UUID matches case-insensitively the first 8 characters of UDF Volume Set Identifier. In that algorithm was chosen UTF-8 encoding because it is the only commonly used Unicode transformation to bytes with fixed points in all hexadecimal digits.

Exit Status

udflabel returns 0 if successful, non-zero if there are problems like block device does not contain UDF filesystem or updating failed.


udflabel is not able to set new Label, Logical Volume Identifier and File Set Identifier for disks with Metadata Partition (used by UDF revisions higher then 2.01) or Virtual Allocation Table (used by Write Once media).

udflabel prior to version 2.1 was not able to read Label correctly if the disk has Virtual Allocation Table stored outside of Information Control Block.


Pali Rohár <pali.rohar@gmail.com>


udflabel is part of the udftools package since version 2.0 and is available from https://github.com/pali/udftools/.

See Also

mkudffs(8), pktsetup(8), cdrwtool(1), udfinfo(1), wrudf(1)

Referenced By

mkudffs(8), udfinfo(1).

udftools Commands