Seems to be fixed since Ubuntu Jammy 22.04.1 has been released, "rw"
kernel parameter as a workaround of the read-only RootFS isn't necessary
anymore.
** Changed in: systemd (Ubuntu)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/1968135
Title:
BTRFS root subvolume @ mounted always as readonly (... ro
rootflags=subvol=@ ...) on Jammy beta
Status in systemd package in Ubuntu:
Fix Released
Bug description:
= Description =
On Ubuntu Jammy Jellyfish (beta 220330) where root (/) is installed on single
BTRFS formated partition (no LVM, no separate /boot), then root subvolume
(subvol=@) is always mounted as read only. There is a kernel flag (ro) appended
to GRUB configuration file /boot/grub/grub.cfg created by script
/usr/sbin/update-grub during every kernel update. Only home subvolume (@home)
remains mounted as rw according to fstab which is correct. Read-only mounted
root (/) leads to many issues.
Image: Jammy Beta (220330)
= Steps to Reproduce =
1. Install Jammy Beta (220330) on EFI PC x86_64 GPT partitioning and select
FS root (/) to one single BTRFS partition (where subvolumes @ and @home are
created). There are only 3 partitions EFI system partition (/dev/sda1), one
swap (sda2), and one BTRFS formated (/dev/sda3) for FS root (/).
2. Launch the kernel via the default grub entry (or look for kernel boot
parameters pressing <e>) - root subvolume (@) is mounted as readonly.
= Expected Results =
root / should be mounted as rw (mount -v | grep @), there should be no (ro)
flag in /proc/cmdline for FS root. It is possible to temporarily avoid this
behaviour in /etc/defaul/grub:
GRUB_CMDLINE_LINUX_DEFAULT="rw quiet splash"
Then there still remains "ro" kernel parameter which is followed by "rw quiet
splash" at the end.
= Actual Results =
in grub.cfg:
linux /@/boot/vmlinuz-5.15.0-23-generic root=UUID=xxxx-xxxx-...
rootflags=subvol=@ ro quiet splash $vt_handoff
in /proc/cmdline:
BOOT_IMAGE=/@/boot/vmlinuz-5.15.0-25-generic
root=UUID=981dd6de-02fc-41a9-9e2a-09dbbc776b2b ro rootflags=subvol=@ quiet
splash vt.handoff=7
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