## Symptom The `systemd-remount-fs.service` service fails to start: ``` Apr 11 11:25:25 fedora systemd-remount-fs[837]: mount: /: fsconfig system call failed: overlay: No changes allowed in reconfigure. Apr 11 11:25:25 fedora systemd-remount-fs[837]: dmesg(1) may have more information after failed mount system call. Apr 11 11:25:25 fedora systemd[1]: Starting systemd-remount-fs.service - Remount Root and Kernel File Systems... Apr 11 11:25:25 fedora systemd[1]: systemd-remount-fs.service: Main process exited, code=exited, status=1/FAILURE Apr 11 11:25:25 fedora systemd[1]: systemd-remount-fs.service: Failed with result 'exit-code'. Apr 11 11:25:25 fedora systemd[1]: Failed to start systemd-remount-fs.service - Remount Root and Kernel File Systems. ``` ## Workaround * If you want to keep using or enable on-demand zstd compression for your main btrfs partition, update your kernel arguments to match what's in your `/etc/fstab`: ``` $ grep 'root' /etc/fstab # UUID=... / btrfs subvol=root,compress=zstd:1,ro 0 0 $ cat /proc/cmdline ... rootflags=subvol=root ... $ sudo rpm-ostree kargs --delete=rootflags=subvol=root -- append=rootflags=subvol=root,compress=zstd:1 ``` * Then comment the entry for `/` in your `/etc/fstab`. Make sure that any future changes to the root mount point options are added to the kernel command line. * Reboot for the changes to apply. ## Original issue With composefs in F42 (https://gitlab.com/fedora/ostree/sig/-/issues/35), the mount options set for the root filesystem in /etc/fstab are not taken into account anymore as `/` is now an overlay mount point. One notable option on default Atomic Desktops installation in zstd compression for btrfs: https://fedoraproject.org/wiki/Changes/BtrfsTransparentCompression ``` silverblue@fedora:~$ cat /etc/fstab # /etc/fstab # Created by anaconda on Wed Feb 12 13:48:11 2025 # # Accessible filesystems, by reference, are maintained under '/dev/disk/'. # See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info. # # After editing this file, run 'systemctl daemon-reload' to update systemd # units generated from this file. # # Updated by bootc-fstab-edit.service UUID=15200db3-8480-4c87-93de-7127a3cb1315 / btrfs subvol=root,compress=zstd:1,ro 0 0 UUID=ff7188f3-e5e5-44c5-8763-93b7ef13a27e /boot ext4 defaults 1 2 UUID=523B-489E /boot/efi vfat umask=0077,shortname=winnt 0 2 UUID=15200db3-8480-4c87-93de-7127a3cb1315 /home btrfs subvol=home,compress=zstd:1 0 0 UUID=15200db3-8480-4c87-93de-7127a3cb1315 /var btrfs subvol=var,compress=zstd:1 0 0 silverblue@fedora:~$ sudo journalctl -u bootc-fstab-edit.service Feb 13 14:14:50 fedora bootc[702]: Updated /etc/fstab to add `ro` for `/` ``` Options: - Mask [systemd-remount-fs.service](https://www.freedesktop.org/software/systemd/man/latest/systemd-remount-fs.service.html) and rely on kernel command line arguments only. - We would have to create something that does a one time sync of `/etc/fstab` options to the kernel command line to migrate existing systems. - New systems need to have those options added as kargs by Anaconda. - This is not ideal as all custom `/proc`, `/sys`, etc. custom mount options would also be ignored. - Teach systemd-remount-fs.service to properly remount /sysroot instead of `/`. See: - https://github.com/bootc-dev/bootc/issues/971 - https://bugzilla.redhat.com/show_bug.cgi?id=2348934 - https://bugzilla.redhat.com/show_bug.cgi?id=2332319 - https://github.com/fedora-iot/iot-distro/issues/81