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VirtioFS host folder into VM with fstab automount ​

GOAL

Share a host folder from UGOS Pro into a Linux VM using virtiofs, and have it mounted via /etc/fstab without breaking boot. We also use bindfs inside the VM so your VM user has correct read/write permissions, and files created inside the VM map correctly to UGOS's user and "admin" group (GID 10).

WARNING

This guide was written for UGOS Pro only, and was last tested with the version 1.13.x

1. On the UGOS host: add virtiofs to the VM ​

  1. SSH into the UGOS host and become root:

    bash
    ssh root@<ugos-host>
    • or ssh <username>@<ugos-host> then:
    bash
    sudo -i   # if sudo exists, otherwise use whatever UGOS provides for root

  2. Find your VM name in libvirt:

    bash
    virsh list --all

    NOTE

    The Name will be in the format of a UUID, e.g. "f229f5ce-b904-4027-a50b-ba24b1d8e2ea"

  3. Dump the VM XML to a temp file:

    bash
    virsh dumpxml <vm-name> > /tmp/vm-config.xml

  4. Edit /tmp/vm-config.xml and add shared memory backing at top level (as a direct child of <domain>, not inside <devices>):

    xml
    <memoryBacking>
    <access mode='shared'/>
    <source type='memfd'/>
</memoryBacking>

    Place it anywhere before <devices>, as long as it’s a sibling of <memory>, <vcpu>, <devices>, etc.

  5. In the same XML file, inside the <devices> section, add a filesystem block:

    NOTE

    Modify the /volume1/projects path below to the full path of your shared folder. You can rename the 'tag' in the <target dir=...> field too; remember this tag for later.

    xml
    <devices>
    ...
    <filesystem type='mount' accessmode='passthrough'>
    <driver type='virtiofs'/>
    <source dir='/volume1/projects'/>
    <target dir='projects-fs'/>
    </filesystem>
    ...
</devices>
    • Replace /volume1/projects with the host path you want to mount.
    • The <target dir='projects-fs'/> string is the tag the VM will mount. Remember this tag exactly (case‑sensitive).

  6. Redefine the VM from the modified XML:

    bash
    virsh define /tmp/vm-config.xml

  7. Restart the VM so the new config is applied:

    bash
    virsh shutdown <vm-name>
virsh start <vm-name>

2. Inside the VM: Install bindfs and create mount points ​

Because UGOS forces passthrough access mode for virtiofs, the mount will show up owned by root:root with strict permissions. We use bindfs to remap this safely for your normal user without modifying the host.

  1. Log into the VM (console or SSH).

  2. Install bindfs (Debian/Ubuntu example):

    bash
    sudo apt update
sudo apt install bindfs

  3. Create two mount points (one raw/hidden, and one for your user):

    bash
    sudo mkdir -p /mnt/.projects-raw
sudo mkdir -p /mnt/projects
    • projects-fs must exactly match the <target dir='...'/> tag in the VM XML.
    • If this works and /mnt/projects shows the host files, proceed to edit /etc/fstab for automount, otherwise fix the issue before continuing.

3. Configure fstab with virtiofs and bindfs ​

We will mount the raw virtiofs share to the hidden folder, then use bindfs to present it to the final folder with the correct user permissions.

  1. Edit /etc/fstab in the VM:

    bash
    sudo nano /etc/fstab

  2. Add these two lines. (Assume your VM user's UID is 1000, and UGOS expects files to be created with group "admin", which is GID 10):

    NOTE

    It works best if the USERNAME inside your VM matches the USERNAME in UGOS that you want to have ownership of the files created inside this folder.

    NOTE

    If you don't know the UID of your VM user, run this command: id $USER. The admin GID of 10 is required by UGOS, please don't change that.

    fstab
    # 1. Mount raw virtiofs to a hidden staging folder
projects-fs  /mnt/.projects-raw  virtiofs  nofail,x-systemd.automount,x-systemd.device-timeout=10  0  0

# 2. Use bindfs to remap ownership and permissions to your user
bindfs#/mnt/.projects-raw  /mnt/projects  fuse  force-user=1000,force-group=1000,create-as-user,create-for-group=10,chown-ignore,chgrp-ignore,perms=0770,nofail,x-systemd.requires=/mnt/.projects-raw  0  0

    What these flags do:

    • x-systemd.automount: Defers mounting until first access so it doesn't break VM boot timing.
    • force-user=1000,force-group=1000,perms=0770: Makes /mnt/projects completely readable/writable by your VM user (UID/GID 1000).
    • create-as-user,create-for-group=10: Ensures files created by your VM user map correctly to your host user and the UGOS admin group (GID 10).
    • chown-ignore,chgrp-ignore: Prevents permission errors when the VM OS attempts to change ownership on the FUSE mount.

  3. Reload systemd units so the new fstab is recognized:

    bash
    sudo systemctl daemon-reload

4. Verify automount works ​

  1. Trigger the automount by accessing the raw folder, then mount the bindfs layer:

    • (Alternatively, just reboot the VM).
    bash
    ls /mnt/.projects-raw
sudo mount /mnt/projects

  2. Verify ownership:

    bash
    ls -ld /mnt/projects
    • It should now show drwxrwx--- youruser yourgroup ... /mnt/projects.

  3. Optional: confirm with mount:

    bash
    mount | grep projects-fs
    • or:
    bash
    mount | grep /mnt/projects
    • You should see a line showing projects-fs mounted on /mnt/projects with type virtiofs.

  4. Test file creation:

    As your non-root user, create a file:

    bash
    touch /mnt/projects/test-file.txt
    • If you check this file on the UGOS host via SSH (ls -l /volume1/projects/test-file.txt), it will correctly show as owned by your UGOS user and the admin group.

5. Common gotchas to double‑check ​

  • The tag in fstab (projects-fs) must exactly match the <target dir='...'/> tag in the VM XML.
  • If you ever edit the VM via the UGOS GUI, you may lose the <filesystem> block. If the mount suddenly fails, re‑add the XML block and restart the VM.

Credit

This guide was created by Drauku