I hate to bitch but bitch I must

michael michael.copeland at gmail.com
Sat Oct 17 22:51:39 UTC 2009

PJ wrote:
> michael wrote:
>> PJ wrote:
>>> Why is it that the manual pages, as thorough as they may be, are very,
>>> very confusing.
>>> Perhaps I am being too wary, but I find that too many
>>> instructions/examples are stumbling blocks to appreciation of the whole
>>> system:
>>> for instance, let's look at the instructions for changing disk labels
>>> with glabel or is it tunefs ?
>>> man glabel(8):
>>> for UFS the file system label is set with
>>> tunefs(8)
>>> <http://www.freebsd.org/cgi/man.cgi?query=tunefs&sektion=8&apropos=0&manpath=FreeBSD+7.2-RELEASE>.
>>> what happened to glabel?
>>> man tunefs(8)
>>> The *tunefs* utility cannot be
>>> run on an active file system. To change an active file system, it must
>>> be downgraded to read-only or unmounted.
>>> So, you have to run tunefs from an active file system to modify another
>>> disk?
>>> but from man tunefs:
>>> BUGS
>>> This utility should work on active file systems.
>>> What in hades does this mean--just above it says cannot be run on active
>>> file systems. ???
>>>  To change the root file
>>> system, the system must be rebooted after the file system is tuned.
>>> You can tune a file system, but you cannot tune a fish.
>>> How cute... And fish eat bugs.
>>> Seriously, now to the manual:
>>> To create a permanent label for a UFS2 file system without destroying
>>> any data, issue the following command:
>>> # tunefs -L /home/ /dev/da3
>>> Oh? home is what? What does this have to do with the partitions?
>>> Here's from man glabel(8):
>>> The following example shows how to set up a label for disk ``da2'', cre-
>>> ate a file system on it, and mount it:
>>> glabel label -v usr /dev/da2
>>> newfs /dev/label/usr
>>> mount /dev/label/usr /usr
>>> [...]
>>> umount /usr
>>> glabel stop usr
>>> glabel unload
>>> The next example shows how to set up a label for a UFS file system:
>>> tunefs -L data /dev/da4s1a
>>> mount /dev/ufs/data /mnt/data
>>> Am I to understand that glabel is only for a new system? What's with the
>>> newfs... I'm trying to set labels on an system that is already set up.
>>> And, the glabel examle above is not for UFS file systems? Oh, that's for
>>> tunefs?
>>> So why are we even dealing with this glabel?
>>> from manual:
>>> # tunefs -L /home/ //dev/da3/
>>> A label should now exist in /dev/ufs which may be added to /etc/fstab:
>>> /dev/ufs/home /home ufs rw 2 2
>>> Why? Is this necessary? and somewhere I saw "tunefs -L volume
>>> /dev/da0s1a" or something like that. Does that mean that each partition
>>> should be tunefsd? Maybe the guys who programmed this stuff understand;
>>> I sure don't. I just want to be able to set the labels according to what
>>> they say can be done... so shy not have a clear and concise explanation?
>>> Do people who write this stuff ever read it? Tell me that its clear and
>>> simple and to the point... so far, I have been running back and forth
>>> between half a dozen web pages trying to understand what is going
>>> on... and doing things through a dense fog does not produce creative
>>> results!
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>> ok, in short since i didn't see anyone answer this directly, your
>> question of tunefs vs glabel:
>> tunefs is for UFS: it labels a UFS filesystem, no matter the device,
>> ie: ad or da. tunefs is part of the filesystem utilities for UFS.
>> good example, can't tunefs -L SWAP /dev/ad0s1b if it is a swap. you
>> can glabel it.
>> glabel is for labeling a device itself. you can glabel an ntfs
>> filesystem or ext2, whatever.
> Thanks for that, Michael.
> But can you explain what this means? It just is not clear for me.
> "# tu;nefs -L home /dev/da3"
> This puts a label on that disk? So now it can be referred to as home?
> da3 = home ?
> I'll try to delve into the man glabel further... but things still look
> murky.
tunefs -L HOME /dev/da3 will put the label /dev/ufs/HOME pointing to 
/dev/da3 . da3=home. exactly correct.
the main idea behind that is that you can move the device around, etc. 
since fstab is looking in /dev/ufs/NAMES_OF_DISKS/PARTITIONS instead of 
/dev/da[0-9] type setup. you can move it to any controller and still 
boot(if you have the driver for the controller).

the glabel command can label ANY disk/slice/partition. its great when 
you get away form the old mbr setup and switch to gpt. gpt lets you have 
an arbitrary number of partitions. and when you think about it, names 
are so much better than numbers anyway, its why we use DNS on networks. 
imagine having to remember every ip you have to use.


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