Re: how to track down cause for EBUSY on /dev/vda4?

[Jeff Moyer <jmoyer@redhat.com>]

Chris Murphy <lists@colorremedies.com> writes:

> Hi,
>
> Short version:
> # mkfs.any /dev/vda4
> unable to open /dev/vda4: Device or resource busy
>
> Curiously /dev/vda4 is just a blank partition, not in use by anything
> that I'm aware of. And gdisk is allowed to modify the GPT on /dev/vda
> without complaint. This is a snippet from strace of the above command
> at the failure point:
>
> openat(AT_FDCWD, "/dev/vda4", O_RDWR|O_EXCL) = -1 EBUSY (Device or
> resource busy)

[snip]

> format, and /proc/mounts shows
>
> /dev/vda /run/initramfs/live iso9660
> ro,relatime,nojoliet,check=s,map=n,blocksize=2048 0 0

That mount claims the device, and you can't then also open a partition
on that device exclusively.

> So it sees the whole vda device as iso9660 and ro? But permits gdisk
> to modify some select sectors on vda? I admit it's an ambiguous image.
> Is it a duck or is it a rabbit? And therefore best to just look at it,
> not make modifications to it. Yet /dev/vda is modifiable, where the
> partitions aren't. Hmm.

The file system is mounted read-only.  It may be that the /device/ is not
read-only.

HTH,
Jeff