How to Fix ‘Failed to Start Remount Root and Kernel File Systems’ in Ubuntu

Watching Ubuntu start up only for the boot splash to be interrupted by a red failure banner: “[FAILED] Failed to start Remount Root and Kernel File Systems. See ‘systemctl status systemd-remount-fs.service’ for details” brings system startup to a sudden halt. In Ubuntu and Debian-derived Linux systems, systemd-remount-fs.service is an early-boot systemd service responsible for remounting the root filesystem (which the initial RAM disk mounts as read-only) with the specific read-write mount options and filesystem parameters defined in /etc/fstab. When an invalid mount option is entered, the root filesystem contains journal corruption, or obsolete parameters are configured in the kernel bootloader line, systemd fails to transition the filesystem into read-write mode. This guide details how to diagnose the systemd unit failure, fix fstab syntax, and restore clean boots in Ubuntu.

Why Does systemd-remount-fs.service Fail?

Because this service executes in the initial seconds of system startup, strict filesystem validation applies. Primary causes include:

• Invalid Mount Options in /etc/fstab: Specifying mount options not supported by the filesystem (for example, applying data=ordered to an XFS or Btrfs partition, or entering typographical errors in errors=remount-ro).
• Dirty or Damaged Filesystem Inodes: Power loss or hard system resets leaving uncommitted metadata transactions that require a manual fsck scan.
• Conflicting Kernel Command Line Parameters in GRUB: Outdated root mount flags passed by the bootloader in /etc/default/grub.
• Missing Required Filesystem Driver Modules: Custom compiled kernels lacking built-in support for the root storage partition filesystem.

Method 1: Inspect Detailed Error Logs in the Maintenance Shell

Querying the failed systemd service directly reveals the exact line number and parameter causing the rejection.

1. If dropped into an emergency or maintenance shell, enter your root/sudo password to proceed.
2. Inspect the status of the remount service:

   systemctl status systemd-remount-fs.service

3. Read the log lines. The output will explicitly identify the offending mount entry (for example: /etc/fstab: line 3: unknown mount option 'commit' or mount: /: can't find UUID=...).
4. Note the cited line number in /etc/fstab.

Method 2: Remount Root as Read-Write and Correct /etc/fstab

You must manually remount the root filesystem before editing configuration files.

1. Remount the root partition in read-write mode:

   mount -o remount,rw /

2. Open the filesystem configuration file in nano:

   nano /etc/fstab

3. Locate the root mount entry (marked with / in the mount point column).
4. Verify that the options column contains valid defaults:

   UUID=xxxx-xxxx  /  ext4  errors=remount-ro  0  1

5. Ensure there are no trailing commas, extra spaces, or unsupported options.
6. Save the file (Ctrl + O, Enter) and exit (Ctrl + X).

Method 3: Run Manual fsck on the Root Filesystem

If filesystem journal corruption prevented systemd from remounting cleanly, executing an integrity check repairs damaged superblocks.

1. Reboot your computer and hold Shift (or press Esc) to display the GRUB boot menu.
2. Select Advanced options for Ubuntu.
3. Select the entry ending in (recovery mode).
4. In the Recovery Menu, use the arrow keys to highlight fsck – Check all file systems and press Enter.
5. Confirm that you want the drive remounted in read-write mode. The system will scan all partitions, resolve orphaned inodes, and repair filesystem journal structures.
6. Once complete, select resume – Resume normal boot.

Method 4: Test and Verify the Remount Service

Testing the service before rebooting confirms that the failure state has been cleared.

1. In your shell, start the remount service manually:

   systemctl start systemd-remount-fs.service

2. Check the service status:

   systemctl is-active systemd-remount-fs.service

3. If the output returns active, the issue is completely resolved. Reboot your system normally:

   systemctl reboot