MongoDB Error – IllegalOperation: Attempted to create a lock file on a read-only directory

The Problem

If you’ve encountered the ‘MongoDB Error – IllegalOperation: Attempted to create a lock file on a read-only directory,’ then you’re likely trying to start a MongoDB instance without the proper access to the file system. This tutorial outlines several methods to troubleshoot and fix this issue.

Solution 1: Check MongoDB Directory Permissions

The error can be caused by inadequate permissions on the directory where MongoDB stores its data files. It is crucial that the user running the MongoDB process has the necessary read and write permissions.

1. Check the current permissions of the MongoDB data directory by running ‘ls -l’ on the directory path.
2. If the permissions are restricted, change them using ‘chmod’ to allow the MongoDB user to read, write, and execute. For instance, ‘sudo chmod 755 /var/lib/mongodb’.
3. Once permissions are set correctly, restart the MongoDB service.

Commands:

$ ls -l /var/lib/mongodb
$ sudo chmod 755 /var/lib/mongodb
$ sudo systemctl restart mongod

Notes: This solution requires root or sudo access. Use with caution, as incorrectly setting permissions can affect system security. Ensure only the MongoDB user has access to its data directory.

Solution 2: Correct Ownership of MongoDB Data Directory

The MongoDB user should own its data directories. If the ownership is incorrect, attempts to write will fail, resulting in this error.

1. Check the ownership using ‘ls -l’ and note the user and group.
2. If incorrect, change ownership with ‘sudo chown’. For example, ‘sudo chown mongodb:mongodb /var/lib/mongodb’ to set both user and group ownership to ‘mongodb’.
3. Once the ownership is correct, attempt to start MongoDB again.

Example:

$ ls -l /var/lib/mongodb
$ sudo chown mongodb:mongodb /var/lib/mongodb
$ sudo systemctl start mongod

Notes: Be careful when assigning ownership. Only the MongoDB user and group should have control over these files to maintain security.

Solution 3: Remount Filesystem with Write Permissions

The filesystem could be mounted as read-only. Remounting the filesystem with write permissions can resolve the error.

1. Determine the mount point for the data directory using ‘mount’ or ‘df’.
2. Remount the filesystem with write permissions using ‘mount -o remount,rw’.
3. After remounting, start MongoDB to see if the issue is resolved.

Commands:

$ df -h /var/lib/mongodb
$ sudo mount -o remount,rw /dev/sdXN /mount_point
$ sudo systemctl start mongod

Notes: This operation requires root access and should be done with caution as it affects the entire filesystem’s state. Make sure that remounting in write mode does not conflict with any system policies or security considerations.

Solution 4: Verify and Repair Filesystem

Filesystem corruption can lead to read-only mode to prevent data loss. A filesystem check and repair using ‘fsck’ may be necessary.

1. Unmount the affected filesystem (if it is not the root filesystem).
2. Run ‘fsck’ on the device to check and repair the filesystem.
3. Remount the device and restart MongoDB.

Commands:

$ sudo umount /var/lib/mongodb
$ sudo fsck /dev/sdXN
$ sudo mount /dev/sdXN /var/lib/mongodb
$ sudo systemctl start mongod

Notes: This process may result in data loss if the filesystem is severely corrupted. Always backup data before attempting repair. Do not run ‘fsck’ on mounted filesystems as it can cause further data corruption.

Conclusion

In conclusion, the ‘MongoDB Error – IllegalOperation: Attempted to create a lock file on a read-only directory’ is typically due to permission issues or a read-only filesystem state. The solutions provided in this guide can help you recover from this error and prevent it from recurring. Always back up your data before performing system-level operations, and ensure that any changes made adhere to security best practices.