Stuck with an error Unable to allow access for disk path in libvirtd? We can help you.

Recently one of our customer using a guest virtual machine informed that he was unable to migrate because libvirt cannot access the disk image(s):

The error looks like the one given below:

# virsh migrate qemu qemu+tcp://name_of_host/system
error: Unable to allow access for disk path /var/lib/libvirt/images/qemu.img: No such file or directory

Here at Bobcares, we fix similar errors for our customers as a part of our Server Management Services. Today, let’s see how our Support Engineers fix this issue for our customers.

How to fix Unable to allow access for disk path in libvirtd

Before going into a fix, we will see what causes this error or issue in libvirtd.

Cause for this Error:

Generally, migration only transfers the in-memory state of a running guest (such as memory or CPU state). Although disk images are not transferred during migration, they need to remain accessible at the same path by both hosts.

Steps to fix this Error:

We need to set up and mount shared storage at the same location on both hosts. This can be done in the simplest way using NFS.

We can do this using the following steps:

1. Firstly, we will set up an NFS server on a host serving as shared storage.

We can use the following command:

# mkdir -p /exports/images
# cat >>/etc/exports <<EOF
/exports/images 192.168.122.0/24(rw,no_root_squash)
EOF

2. Mount the exported directory at a common location on all hosts running libvirt.

We can use the following command:

# cat >>/etc/fstab <<EOF
123.123.123.123:/exports/images /var/lib/libvirt/images nfs auto 0 0
EOF
# mount /var/lib/libvirt/images

Note: replace Ip with the address of the NFS server.

If the above configuration is not set up correctly, the guest virtual machine may lose access to its disk images during migration. This is because the source host’s libvirt daemon may change the owner, permissions, and SELinux labels on the disk images after it successfully migrates the guest to its destination.

Once libvirt detects that the disk images are mounted from a shared storage location, it will not make these changes.

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Conclusion

In short, we saw the steps that our Support Engineers follow to fix the error Unable to allow access for disk path in libvirtd.