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/.