I am having a hard time configuring a shared folder with write permissions inside the guest. My special case is that the shared folder references a CIFS network share mounted on the host.

Host configuration

Network share (and shared folder) /media/nas/temp is mounted via

sudo mount -t cifs -o username=dave,vers=3.0,uid=dave,gid=libvirt-qemu //nas/temp /media/nas/temp

Virt-manager configuration:

enter image description here

Permissions from host perspective:

dave@host:~$ ll /media/nas/
drwxr-xr-x 2 dave        libvirt-qemu    0 Dez  6 15:36 temp/

Guest configuration

/temp (/media/nas/temp on host) is mounted via:

sudo mount -t 9p -o trans=virtio,version=9p2000.L /temp /media/temp

Permissions from guest perspective (64055 is the uid of libvirt-qemu group of the host):

dave@guest:~$ ll /media
drwxr-xr-x  2 dave 64055    0 dec  6 15:36 temp/


A write operation like creating a new file triggers following error:

dave@guest:~$ touch /media/temp/myfile.log
touch: cannot touch '/media/temp/myfile.log': Permission denied

I also tried file_mode and dir_mode mount options from the host:

sudo mount -t cifs -o username=dave,vers=3.0,uid=dave,gid=libvirt-qemu,\
  file_mode=0777,dir_mode=0777 //nas/temp /media/nas/temp

New permissions from host perspective:

dave@host:~$ ll /media/nas
drwxrwxrwx 2 dave        libvirt-qemu    0 Dez  6 15:36 temp/

Curiously, now I get a different error:

dave@guest:~$ touch /media/temp/myfile.log
touch: cannot touch '/media/temp/myfile.log': Operation not supported

What works

  1. The host can write to /media/nas/temp with user dave.

  2. From within the guest, I could mount via CIFS directly successfully (same credentials) - but that is not possible in my current environment.

  3. I am also able to mount a local host folder (like /home/dave/Downloads/qemu-test, which has the exact same permissions, and write to it. Permissions in this case were:

dave@host:~$ ll ~/Downloads/
drwxrwx---+  2 dave libvirt-qemu    4096 Dez  6 17:25 qemu-test/


Why does it make a difference, if I want to share a network or local folder via mount -t 9p? As shown, the permissions should be the same and it shouldn't matter for the guest, what kind of mountpoint is shared (?).

Has anybody managed to do write a shared folder mounted as network share from host (if yes, how)?


Similar posts, which are about sharing a local folder:


After a bit more investigation, here is what worked for me. Important points:

  1. set mount mode to Squash - neither Passthrough nor Mapped.
  2. set mount point owner to libvirt-qemu and the group to dave (user/uid used in the guest).
  3. set file_mode=0755, dir_mode=0755 in the mount CIFS options.

Example mount (host):

sudo mount -t cifs -o username=dave,vers=3.11,uid=libvirt-qemu,gid=dave,file_mode=0775,dir_mode=0775 //nas/temp /media/nas/temp

Ad 1.: In other modes, I got errors like

touch: setting times of xxx: No such file or directory

touch: cannot touch '/media/temp/myfile.log': Operation not supported

Ad 2.: It wasn't sufficient to set libvirt-qemu as group, resulting in "Permission denied" errors. In the question, I did it the other way round. Make sure to select the correct UID for the guest - e.g. set the same UIDs for dave on the host and guest. Note: the QEMU/KVM virtual machine is run as user libvirt-qemu.

Ad 3.: These options make the mountpoint writeable for user dave, whose group is set as owning group (standard would be readonly).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.