[fedora-virt] guestfish, libguestfs, ext4 and bad perms on /dev/kvm

Richard W.M. Jones rjones at redhat.com
Wed Apr 22 21:41:55 UTC 2009

On Wed, Apr 22, 2009 at 05:27:12PM -0400, Robert P. J. Day wrote:
> On Wed, 22 Apr 2009, Richard W.M. Jones wrote:
> > On Wed, Apr 22, 2009 at 03:20:14PM -0400, Robert P. J. Day wrote:
> > >   in short, ext4 filesystem support now appears to work, but
> > > there's still the issue (perhaps addressed earlier) that non-root
> > > users don't have access to KVM support but, from the perspective
> > > of libguestfs, does that really matter?
> >
> > KVM makes things do a lot faster, which is always nice.
>   which inspires the obvious question -- is kvm *required* for any
> libquestfs functionality?  speed is always nice, but it's important to
> know that, even if things are slow, they will still work equally well.

Short answer: No.  It just makes things go faster.

Longer answer: The QEMU and KVM codebases are slightly different
(although converging).  This means that by using QEMU versus KVM you
may tickle a bug in one which is not in the other.  So it goes.

> > You can
> > do the following:
> >
> >   # chmod o+rw /dev/kvm
> >
> > You have to do (just) that command as root, but after that qemu-kvm
> > and guestfish itself can all be run as non-root, and will benefit
> > from KVM acceleration.
>   or, for permanence, add the appropriate udev rule, which is what i
> prefer, since it persists across reboots.

Indeed.  I never worked out udev, so I tend to add the required chmod
commands into my /etc/rc.local.  Luckily no one employs me as a
sys-admin any more ...


Richard Jones, Emerging Technologies, Red Hat  http://et.redhat.com/~rjones
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