Re: [libvirt] inability to open local read-only connection
On Mon, Jul 12, 2010 at 06:38:27AM -0500, Tavares, John wrote:
Hi Daniel,
Sorry it took so long to back to this. I just recently ran into the
same problem on RHEL 5.5 where I am running into problems using the
root owned setuid executable to get domain information. Basically
all that I needed to do to show this was to modify the example
program dominfo/info1.c that ships with the libvirt source and added
a function that attempts to get any information about that domain.
In this case, I chose the virDomainGetSchedulerType() function. Here
is the output of 3 separate runs, the first will be as a non-root user,
the second is from root and the last is from the same executable but
just root owned setuid and run as a normal user:
I've figured out what is going on here. Originally libvirt provided
a setuid proxy for accessing the Xen driver as non-root. This is
/usr/libexec/libvirt_proxy. This only supports a small sub-set of
API calls and is only for the Xen hypervisor. Later we added a
general purpose daemon (/usr/sbin/libvirtd) that runs as root and
works for all APIs and all hypervisors. This daemon replaces the
setuid proxy, but for reasons of backwards compatability in RHEL5
the proxy is still the default for Xen. The virDomainGetSchedulerType()
API is an example of one that is supported by libvirtd, but not by
the Xen proxy. To force use of the libvirtd, give it an explicit
URI, xen+unix:/// will make it connect to Xen, over libvirtd's
UNIX domain socket.
$ ll info1
-r-xr-xr-x 1 perform perform 9326 Jul 12 16:50 info1
$ whoami
perform
$ ./info1
Domains 0: 2 CPUs
This doesn't print schedular info because it is not supported
by the Xen proxy.
$ su
Password:
# ./info1
Domains 0: 2 CPUs
Scheduler = credit
# chown 0:0 info1;chmod 6555 info1
# ll info1
-r-sr-sr-x 1 root root 9326 Jul 12 16:50 info1
# exit
$ whoami
perform
$ ./info1
Domains 0: 2 CPUs
libvir: Xen Daemon error : this function is not supported by the hypervisor: unsupported
in xendConfigVersion < 4
Not entirely sure why you get this error message here, but
I strongly recommend against running this setuid regardless.
$ virsh version
error: failed to connect to the hypervisor
You need to pass the --readonly flag to virsh
$ whoami
berrange
$ virsh --readonly version
Compiled against library: libvir 0.6.3
Using library: libvir 0.6.3
Using API: Xen 3.0.1
Running hypervisor: Xen 3.1.0
And to make it use the libvirtd instead of the proxy give it a URI:
$ virsh -c xen+unix:/// --readonly schedinfo Domain-0
Scheduler : credit
weight : 256
cap : 0
$ su root -c "virsh version"
Password:
Compiled against library: libvir 0.6.3
Using library: libvir 0.6.3
Using API: Xen 3.0.1
Running hypervisor: Xen 3.1.0
Daniel
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