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Starting a QEMU VM as a Non-root User: Avoiding Permission Issues

Zeyu Jin2020-08-20QEMUPermissionsRoot userlibvirt

Background

In a scenario where multiple users use a VM, each user is a non-root user. When a non-root user runs the virsh command to start a QEMU VM, the user may encounter a lot of problems.

The most common problem is about permissions. For example, when the virsh start command is executed, error message similar to the following may be displayed:

error: Failed to start domain jzy-lts
error: internal error: qemu unexpectedly closed the monitor: 2020-07-14T13:29:11.323694Z qemu-kvm: -drive file=/home/jzy/kvm/openEuler-20.03-LTS.aarch64.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0,cache=none,aio=native: Could not open '/home/jzy/kvm/openEuler-20.03-LTS.aarch64.qcow2': Permission denied

You might think that QEMU has bugs when encountering similar problems. However, improper operations are likely the cause.
The following describes how to start a QEMU VM as a non-root user and avoid possible permission issues.

Procedure

Perform the following steps:

  1. Create a user (for example, jzy) and add it to the kvm group.
[root]    useradd -m jzy
[root]	  gpasswd -a jzy kvm
  1. Modify the /etc/libvirt/qemu.conf file.
# user = "root"
Add the following content:
user = "jzy"
# group = "root"
Add the following content:
group = "jzy"
  1. Restart libvirtd.
[root]    service libvirtd restart
or
[root]    systemctl restart libvirtd.service
  1. Allow the jzy user to use the sudo command.
[root]    vim /etc/sudoers

Add jzy ALL=(ALL) ALL.
Then, save and exit.

  1. Switch to the jzy user, go to the /home/jzy directory, and prepare related files.
    Ensure that the permissions on files and directories are 755.
[jzy@localhost ~]$ pwd
/home/jzy

[jzy@localhost ~]$ ll
total 4.0K
drwxr-xr-x 2 jzy jzy 4.0K Jul 23 11:29 kvm

[jzy@localhost ~]$ ll kvm
total 7.2G
-rwxr-xr-x 1 jzy  jzy  1.6K Jul 23 11:29 openE_jzy.xml
-rwxr-xr-x 1 jzy  jzy  4.4G Jul 23 11:25 openEuler-20.03-LTS-aarch64-dvd.iso
-rwxr-xr-x 1 root root 2.9G Jul 23 11:32 openEuler-image.qcow2
  1. Then, start a VM.
[jzy@localhost ~]$ sudo virsh create kvm/openE_jzy.xml
Domain openEulerVM created from kvm/openE_jzy.xml

Note: Ensure that the owner and group of the file are correct.


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