[libvirt-users] libvirtd via unix socket using system uri

[Daniel P. Berrangé]

On Tue, Apr 30, 2019 at 12:42:11AM +0900, lameventanas at gmail.com wrote:
> 
> 
> On 29/04/2019 22.01, Michal Privoznik wrote:
> > On 4/29/19 1:06 PM, lameventanas at gmail.com wrote:
> >> I want to run libvirtd as a special user, and allowing users that belong
> >> to a special group to connect via qemu+unix:///system (eg: unix socket).
> >>
> >> I did everything necessary to do so: created a libvirt user and group,
> >> added the libvirt user to the kvm group, added my normal user to the
> >> libvirt group, and made sure the socket is owned by libvirt:libvirt with
> >> permissions set to 770.
> >>
> >> libvirtd starts successfully, but when I try to connect as the normal
> >> user I get this error:
> >>
> >> bash$ virsh --connect qemu+unix://system
> >> error: failed to connect to the hypervisor
> >> error: invalid argument: using unix socket and remote server 'system' is
> >> not supported.
> > 
> > This is not valid URI.
> > 
> > https://libvirt.org/uri.html
> > 
> > You may want to use 'qemu+unix:///system' or simply 'qemu:///system'
> > which is the same because libvirt connects via unix socket by default.
> 
> Thanks, I missed that.
> 
> Now I get this:
> 
> $ virsh --connect qemu:///system
> error: failed to connect to the hypervisor
> error: internal error: unexpected QEMU URI path '/system', try
> qemu:///session
> 
> But now I see virsh opening the socket, writing, etc.
> 
> The server log shows this:
> 
> 2019-04-29 15:32:07.306+0000: 20863: info : libvirt version: 5.2.0
> 2019-04-29 15:32:07.306+0000: 20863: info : hostname: koji
> 2019-04-29 15:32:07.306+0000: 20863: error : virDBusGetSessionBus:169 :
> internal error: Unable to get DBus session bus connection: Unable to
> autolaunch a dbus-daemon without a $DISPLAY for X11
> 2019-04-29 15:32:24.534+0000: 20852: error : qemuConnectOpen:1127 :
> internal error: unexpected QEMU URI path '/system', try qemu:///session
> 2019-04-29 15:32:24.534+0000: 20851: error : virNetSocketReadWire:1803 :
> End of file while reading data: Input/output error
> 
> I also wonder if dbus is important, and if so, how to fix it.
> 
> 
> > Anyway, you'll need to run libvirtd privileged, otherwise it'll get
> > EPERM when trying to do almost anything.
> 
> I'm aware of that, I want to try and see the limitations, and maybe get
> around them by using capabilities?

Libvirt has two distinct modes of operation - system mode and session
mode. When uid == 0, libvirtd runs in system mode & offers full
privileges. When uid != 0 it runs in session mode & disables alot of
functionality, or it will simply fail to use it.

It is impossible to run system mode as uid != 0, as it will always
activate session mode in this case.

Regards,
Daniel
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