Section: Maintenance Commands (8)
udflabel --- show or change UDF filesystem label
udflabel [encoding-options] [block-options] [identifier-options] device [new-label]
is invoked without identifier-options
then it shows current label of UDF filesystem on
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
synonym for both --lvid
, see section
UDF LABEL AND UUID
Display the usage and the list of 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
- -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.
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
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
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
2. part: Convert next 4 bytes (9.-12. pos.) to their hexadecimal
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.
returns 0 if successful, non-zero if there are problems like
block device does not contain UDF filesystem or updating failed.
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 <firstname.lastname@example.org>
is part of the udftools package since version 2.0 and is
available from https://github.com/pali/udftools/.