Ubuntu Manpage: udflabel — show or change UDF filesystem label

NAME

       udflabel — show or change UDF filesystem label

SYNOPSIS

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

DESCRIPTION

       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.

OPTIONS

GENERAL OPTIONS
-h,--help
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
Force updating UDF disks without write support or write protected UDF disks. Some UDF disks may
have set write protect flag. 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. Also it
ignores UDF SoftWriteProtect and HardWriteProtected flags.

-n,--no-write
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
--locale
Treat identifier string options as strings encoded according to current locale settings (default).
Must be specified as the first argument.

--u8 Treat identifier string options as strings encoded in 8-bit OSTA Compressed Unicode format without
leading Compression ID byte, which is equivalent to Latin1 (ISO-8859-1). Must be specified as
first argument.

--u16 Treat identifier string options as strings encoded in 16-bit OSTA Compressed Unicode format
without leading Compression ID byte, which is equivalent to UTF-16BE. 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.

--utf8 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.

LIMITATIONS

       udflabel  is  not able to set new Label, Logical Volume Identifier and File Set Identifier for disks with
       Virtual Allocation Table (used by Write Once media).

       udflabel prior to version 2.2 was unable to print and process Unicode  strings  with  code  points  above
       U+FFFF  correctly.  When  option  --utf8  was  specified  then input strings were limited to 3-byte UTF-8
       sequences and when option --u16 was specified then input strings were limited  just  to  UCS-2BE  strings
       (subset of UTF-16BE).

       udflabel  prior  to version 2.2 ignored UDF SoftWriteProtect and HardWriteProtected flags and overwritten
       such disks without any notice.

       udflabel prior to version 2.2 was not able to set a new Label, Logical Volume  Identifier  and  File  Set
       Identifier for disks with Metadata Partition (used by UDF revisions higher then 2.01).

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

AUTHOR

       Pali Rohár <pali.rohar@gmail.com>

AVAILABILITY

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