Recently encountered a frustrating situation where my Ubuntu 9.10 server suddenly mounted its root partition (/dev/sda5) as read-only. Attempting to remount it with write permissions failed with the error:

mount: cannot remount block device /dev/sda5 read-write, is write-protected

Basic file operations like touch confirmed the filesystem was indeed read-only:

touch: cannot touch helll': Read-only file system

Before jumping to conclusions, I verified several key points:

• No multipath configuration involved
• SELinux was inactive
• No RAID setup (just two separate 500GB disks)
• No recent relevant errors in dmesg

The most surprising discovery came after reboot - the BIOS couldn't detect the primary hard drive at all. This explained why the filesystem became read-only: the disk was failing but hadn't completely died yet.

Modern Linux kernels often remount filesystems as read-only when they detect potential disk failures to prevent data corruption.

For others facing similar issues, here are some diagnostic commands that might help:

# Check filesystem status
dmesg | grep -i error
dmesg | grep -i sda

# Check disk health (if drive is still detectable)
smartctl -a /dev/sda

# Alternative mount attempt
mount -o remount,rw /

To avoid being caught off-guard by disk failures:

1. Implement regular SMART monitoring
2. Set up proper backups
3. Consider using RAID for critical systems
4. Monitor system logs for early warning signs

In my case, the solution was hardware replacement. The disk had reached end-of-life and needed to be replaced. After installing a new drive and restoring from backup, the system returned to normal operation.

Remember: When a filesystem suddenly becomes read-only without configuration changes, hardware failure should be your first suspicion.

When your Linux system suddenly mounts a partition as read-only without configuration changes, it typically indicates underlying hardware or filesystem issues. In this case, attempting mount -o rw,remount /dev/sda5 fails with the message:

mount: cannot remount block device /dev/sda5 read-write, is write-protected

Before concluding hardware failure, let's verify these critical points:

• Check filesystem integrity: fsck -n /dev/sda5
• Review kernel messages: dmesg | grep -i sda5
• Inspect SMART status: smartctl -a /dev/sda

Modern filesystems automatically remount as read-only when detecting errors. Common triggers include:

# Check for remount events in syslog
grep -i remount /var/log/syslog

# Verify mount options currently in use
findmnt -o OPTIONS /dev/sda5

In this scenario, the ultimate resolution required hardware replacement. Key indicators were:

• BIOS could no longer detect the drive
• No recent relevant entries in dmesg
• Sudden transition to read-only without configuration changes

Implement these checks to catch issues earlier:

#!/bin/bash
# Basic filesystem health monitor
if findmnt -n -o OPTIONS / | grep -q ro,; then
    echo "ALERT: Root filesystem is read-only!" | mail -s "FS Alert" admin@example.com
fi

# SMART monitoring cron job
smartctl -H /dev/sda || echo "SMART test failed" | mail -s "Drive Alert" admin@example.com

If the drive becomes inaccessible but contains critical data:

1. Immediately stop write operations
2. Consider professional data recovery services
3. For future setups, implement RAID1 at minimum