You have been subscribed to a public bug: Even though the ext4 filesystem is marked read-only, /proc/mounts doesn't show the filesystem as ro and instead shows as rw:
/mnt/wwn-0xxxxxxxxxxxxx$ touch a.txt touch: cannot touch 'a.txt': Read-only file system Mount point shows up as rw in /proc/mounts: egrep ' ro,|,ro ' /proc/mounts tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,size=4096k,nr_inodes=1024,mode=755,inode64 0 0 none /run/credentials/systemd-sysusers.service ramfs ro,nosuid,nodev,noexec,relatime,mode=700 0 0 none /root/backup_agent_home/run/credentials/systemd-sysusers.service ramfs ro,nosuid,nodev,noexec,relatime,mode=700 0 0 findmnt /mnt/wwn-0xxxxxxxxxxxxx/ TARGET SOURCE FSTYPE OPTIONS /mnt/wwn-0xxxxxxxxxxxxx /dev/sdc1 ext4 rw,noatime,errors=remount-ro tune2fs detecting errors: sudo tune2fs -l /dev/sdc1 | grep -i error Filesystem state: clean with errors Errors behavior: Continue FS Error count: 994269354 First error time: Sat Jul 5 05:59:43 2025 First error function: ext4_validate_block_bitmap First error line #: 420 First error err: EFSCORRUPTED Last error time: Mon Aug 18 23:03:31 2025 Last error function: ext4_journal_check_start Last error line #: 83 Last error err: EIO Several errors in dmesg which shows that the kernel does see filesystem errors and is attempt to remount it as read-only: sudo dmesg | grep -i "ext4|error|remount" | tail -20 [5272597.675801] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.675802] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.676045] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.678244] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.688872] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.689167] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.689446] EXT4-fs (sdc1): Remounting filesystem read-only [5272597.692148] EXT4-fs (sdc1): Remounting filesystem read-only After performing a bisect, it seems like all kernels with the commit: https://cos.googlesource.com/third_party/kernel/+/d013eadd440085609f9d97c64263e8122bad2c48 seem to behave in a simlar fashion wherein even though the filesystem is read-only, /proc/mounts does not reflect this behavior. The following versions were validated and we see the same behavior: 5.15.0-131.141 5.15.0-133.144 5.15.0-140.150 /proc/mounts has been the source of truth for several years. How can I find out that a file-system is indeed read-only without actually attempting to write or depend on the kernel logs? I want to fix filesystems that are marked read-only by performing an fsck but /proc/mounts not reflecting this affects my ability to do this proactively. ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Tags: bot-comment kernel-bug -- /proc/mounts does not report read-only filesystems https://bugs.launchpad.net/bugs/2122369 You received this bug notification because you are a member of Kernel Packages, which is subscribed to linux in Ubuntu. -- Mailing list: https://launchpad.net/~kernel-packages Post to : [email protected] Unsubscribe : https://launchpad.net/~kernel-packages More help : https://help.launchpad.net/ListHelp
