Helmut Hullen posted on Mon, 27 Feb 2012 11:27:00 +0100 as excerpted:
> Du meintest am 27.02.12:
>
>>>> mkfs.btrfs creates a new filesystem. The -L option sets the label
>>>> for the newly-created FS.
>>> The safest way may be deleting this option ... it seems to work as
>>> expected only when I create a new FS on 1 disk/partition.
>
>> I've said this several times: Your expectations are wrong. You
>> don't label partitions.
>
> Yes - now I know.
> But I'm afraid other people also expect wrong - when I use mkfs.ext[234]
> then this option works (in another way than with "mkfs.btrfs").
AFAIK, it works in the same way... that is, it labels the, in that case,
ext2/3/4 filesystem, in this case (mkfs.btrfs), btrfs filesystem.
>From the manpages:
mkfs.btrfs (aka mkbtrfs):
-L, --label name
Specify a label for the filesystem.
mkfs.ext2/3/4 (aka mke2fs):
-L new-volume-label
Set the volume label for the filesystem to
new-volume-label. The maximum length of the
volume label is 16 bytes.
e2label:
e2label will display or change the filesystem label on the
ext2, ext3, or ext4 filesystem located on device.
mkreiserfs:
-l | --label LABEL
Sets the volume label of the filesystem. LABEL
can at most be 16 characters long; if it is longer than
16 characters, mkreiserfs will truncate it.
reiserfstune:
-l | --label LABEL
Set the volume label of the filesystem. LABEL can
be at most 16 characters long; if it is longer than 16
characters, reiserfstune will truncate it.
The mkswap manpage does make things a bit more confusing, until you
realize that the "device" they're referencing is a "swap device", which
can be a file, not just a "block device".
mkswap sets up a Linux swap area on a device or in a file.
[...]
-L, --label label
Specify a label for the device, to allow swapon by label.
fstab indicates the filesystem label:
The first field (fs_spec).
This field describes the block special device or remote
filesystem to be mounted.
For ordinary mounts it will hold (a link to) a block
special device node (as created by mknod(8)) for
the device to be mounted, like `/dev/cdrom' or
`/dev/sdb7'. [...]
Instead of giving the device explicitly, one may
indicate the (ext2 or xfs) filesystem that is to
be mounted by its UUID or volume label (cf.
e2label(8) or xfs_admin(8)), writing
LABEL=<label> or UUID=<uuid>, e.g., `LABEL=Boot'[.]
This will make the system more robust: adding
or removing a SCSI disk changes the disk device name
but not the filesystem volume label.
mount seems to be confused, using label in both the filesystem and device
context (it also discusses selinux labels, etc, which are of course
different). I'm not going to quote it here as the bits discussing label
are dispersed and getting context clear on all of them would take a lot
of space. Searching the manpage for "label" (case insensitive search)
works, tho, again noting that it uses "label" in selinux and other
contexts as well.
In another post I mentioned that gpt partitions do have "names", which
/could/ function similarly to labels, tho Linux including the mount
command generally ignores them at present. From the gdisk (part of
gptfdisk) manpage (the cgdisk and sgdisk manpages, same package, are
similarly worded, including the note on the distinction between gpt
partition name and filesystem label):
c Change the GPT name of a partition. This name is encoded
as a UTF-16 string, but proper entry and display of
anything beyond basic ASCII values requires suitable
locale and font support. For the most part, Linux ignores
the partition name, but it may be important in some OSes.
GPT fdisk sets a default name based on the partition type
code. Note that the GPT partition name is different from
the filesystem name, which is encoded in the filesystem's
data structures.
Note especially that last sentence, above.
So a filesystem label is just that, a /filesystem/ label. That there's
normally a 1:1 correspondence between filesystem and the block device(s)
it's on is simply an accident. But it's NOT an accident when a btrfs
filesystem label applies to ALL the devices that compose the filesystem,
since it's a FILESYSTEM label, NOT a PARTITION label. As the gptfdisk
manpages make clear, partition names/labels, where they exist as in gpt
based partitioning, are quite distinct from the filesystem names/labels.
However, the above manpage research does point out that while usage is
generally quite consistent, the mkswap and mount manpages usage is
ambiguous, and should be made more clear.
Perhaps later today I'll file bugs...
--
Duncan - List replies preferred. No HTML msgs.
"Every nonfree program has a lord, a master --
and if you use the program, he is your master." Richard Stallman
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