Changing label of a mounted XFS filesystem

Changing label of a mounted XFS filesystem

[Matthias Schniedermeyer]

Hi


Is there a particular reason that the label of a mounted XFS fileystem
can't be changed?

The man-page of xfs_admin gives a blanket "Devices that are mounted
cannot be modified" but no explanation for why that is.

In my case it's the label of the root-filesystem i want to change. So to
change it i would have to boot the computer with some kind of live or
rescure-system. Or i would need to temporarily connect the device to
another computer, both aren't really nice hoops to jump through just to
change a few characters.

The only thing i can compare this to is ext2 and with ext2 (/boot
partition, so it really is ext2) i can change the label to my hearts
content, even the device is mounted.

For my case i could live with it if i could remount the filesystem RO,
change the label and then having to reboot the machine, still nicer than
the other 2 options.



-- 

Matthias

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Re: Changing label of a mounted XFS filesystem

[Jeff Liu]

Hi,

On 07/03/2014 07:29 PM, Matthias Schniedermeyer wrote:
> Hi
> 
> 
> Is there a particular reason that the label of a mounted XFS fileystem
> can't be changed?

Maybe since we have no user request for this function? :)

> The man-page of xfs_admin gives a blanket "Devices that are mounted
> cannot be modified" but no explanation for why that is.
> 
> In my case it's the label of the root-filesystem i want to change. So to
> change it i would have to boot the computer with some kind of live or
> rescure-system. Or i would need to temporarily connect the device to
> another computer, both aren't really nice hoops to jump through just to
> change a few characters.
> 
> The only thing i can compare this to is ext2 and with ext2 (/boot
> partition, so it really is ext2) i can change the label to my hearts
> content, even the device is mounted.
> 
> For my case i could live with it if i could remount the filesystem RO,
> change the label and then having to reboot the machine, still nicer than
> the other 2 options.

Btrfs support set/change label on a mounted file system via ioctl(2), maybe we
can implement it if that sounds useful to our users.


Cheers,
-Jeff
 

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Re: Changing label of a mounted XFS filesystem

[Matthias Schniedermeyer]

On 03.07.2014 20:07, Jeff Liu wrote:
> Hi,
> 
> On 07/03/2014 07:29 PM, Matthias Schniedermeyer wrote:
> > Hi
> > 
> > 
> > Is there a particular reason that the label of a mounted XFS fileystem
> > can't be changed?
> 
> Maybe since we have no user request for this function? :)
> 
> > The man-page of xfs_admin gives a blanket "Devices that are mounted
> > cannot be modified" but no explanation for why that is.
> > 
> > In my case it's the label of the root-filesystem i want to change. So to
> > change it i would have to boot the computer with some kind of live or
> > rescure-system. Or i would need to temporarily connect the device to
> > another computer, both aren't really nice hoops to jump through just to
> > change a few characters.
> > 
> > The only thing i can compare this to is ext2 and with ext2 (/boot
> > partition, so it really is ext2) i can change the label to my hearts
> > content, even the device is mounted.
> > 
> > For my case i could live with it if i could remount the filesystem RO,
> > change the label and then having to reboot the machine, still nicer than
> > the other 2 options.
> 
> Btrfs support set/change label on a mounted file system via ioctl(2), maybe we
> can implement it if that sounds useful to our users.

I would vote for that, i've run into this particular brickwall several 
times over the years.

I more or less reguarly clone or "move" storage and/or machines around 
and several times i forgot to re-label filesystems "at that point in 
time were it was easily done" and then run into the brickwall when first 
booting whatever i built at that time. Same has happend to me for 
/etc/fstab and/or GRUB configuration. But unless GRUB doesn't boot at 
all it can be rectified without too much hassle.

Yesterday i "fixed" it by changing the fstab to the "wrong" label.

The other solution would be for me to make a checklist, so i don't 
forget such things. But that would be to easy. ;-)



-- 

Matthias

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Re: Changing label of a mounted XFS filesystem

[Dave Chinner]

On Thu, Jul 03, 2014 at 04:14:08PM +0200, Matthias Schniedermeyer wrote:
> On 03.07.2014 20:07, Jeff Liu wrote:
> > Hi,
> > 
> > On 07/03/2014 07:29 PM, Matthias Schniedermeyer wrote:
> > > Hi
> > > 
> > > 
> > > Is there a particular reason that the label of a mounted XFS fileystem
> > > can't be changed?
> > 
> > Maybe since we have no user request for this function? :)

Most likely. It's currently done by xfs_db, which is an offline
tool.

> > > The man-page of xfs_admin gives a blanket "Devices that are mounted
> > > cannot be modified" but no explanation for why that is.
> > > 
> > > In my case it's the label of the root-filesystem i want to change. So to
> > > change it i would have to boot the computer with some kind of live or
> > > rescure-system. Or i would need to temporarily connect the device to
> > > another computer, both aren't really nice hoops to jump through just to
> > > change a few characters.
> > > 
> > > The only thing i can compare this to is ext2 and with ext2 (/boot
> > > partition, so it really is ext2) i can change the label to my hearts
> > > content, even the device is mounted.
> > > 
> > > For my case i could live with it if i could remount the filesystem RO,
> > > change the label and then having to reboot the machine, still nicer than
> > > the other 2 options.
> > 
> > Btrfs support set/change label on a mounted file system via ioctl(2), maybe we
> > can implement it if that sounds useful to our users.
> 
> I would vote for that, i've run into this particular brickwall several 
> times over the years.

There's a bunch of things I'd like to make online modifiable that
currently can only be done offline by xfs_db and other tools. I'll
add this to the list, and hopefully when I get a little time I'll do
something about it...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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