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 show current label of UDF filesystem on device to standard  output  terminated  by  new
       line.  Otherwise  it  update  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 power
of two in range from 512 to 32768 and must match a device logical (sector) size. If
omitted, udflabel tries to autodetect block size. 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 is necessary to specify correct location.

Virtual Allocation Table on disks with UDF revisions higher then 1.50 contains
Logical Volume Identifier (UDF Label).

--force
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 overwrite existing Label or
Identifiers also for UDF filesystem which has Access Type either Read-Only or
Recordable (Write-Once). This is possible only if underlaying 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 treat
it as Overwritable.

-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 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 first argument.

--u8 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.

--u16 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 first argument.

--utf8 Treat identifier string options as strings encoded in UTF-8. Must be specified as
first argument.

UDF LABEL AND UUID

UDF specification does not say anything about a disk label but describe that UDF Logical
Volume Identifier is 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 majority of UDF implementations to use UDF Logical Volume Identifier as a UDF disk
label.

UDF specification does not have 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). Because there are still 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 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 Metadata Partition (used by UDF revisions  higher  then  2.01)  or  Virtual
       Allocation  Table  (used by Write Once media). Also is not able to read Label correctly if
       disk has 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/.