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If you encounter an error message like:

Read-only file system

when trying to execute disk write operations (e.g., tar, cp, mv, rm, chmod, chown, wget), it means your Linux filesystem is mounted as read-only, preventing any write operations.

📌 In this guide, you’ll learn:
✅ Why your filesystem is stuck in read-only mode
✅ How to diagnose whether the issue is caused by disk corruption, filesystem errors, or misconfiguration
✅ Step-by-step solutions to restore read-write (RW) mode
✅ Preventive measures to avoid this issue in the future

🛑 1. Why is the Filesystem Read-only?

Your Linux filesystem may become read-only due to one of the following reasons:

🔹 Filesystem corruption – Sudden power loss, improper shutdown, or unclean filesystem state
🔹 Disk failure or bad sectors – The disk is failing, triggering the OS to mount it as read-only
🔹 Misconfigured /etc/fstab file – Incorrect mount options, partition type mismatch (e.g., using ntfs instead of ext4)

Before fixing the issue, let’s first diagnose the root cause.

🔍 2. Diagnosing the Read-only Filesystem Issue

To identify the cause of the problem, follow these diagnostic steps.

🔹 Step 1: Check System Logs for Clues

Run the following command to check logs:

dmesg | tail -50

📌 If you see messages like:

EXT4-fs error (device sda1): ext4_journal_check_start:56: Detected aborted journal

➡️ The issue is likely filesystem corruption.

📌 If you see disk I/O errors like:

blk_update_request: I/O error, dev sda, sector 123456

➡️ The problem is likely a failing hard drive.

🔹 Step 2: Check the Mount Status

Verify how your filesystem is currently mounted:

mount | grep ' ro,'

📌 If you see:

/dev/sda1 on / type ext4 (ro,errors=remount-ro)

➡️ The system automatically mounted the filesystem as read-only due to errors.

🔹 Step 3: Verify Disk Health

Check the disk for bad sectors:

smartctl -H /dev/sda

📌 If the result is "FAILED" or "PRE-FAIL", the disk may be failing.

Run a deeper analysis:

smartctl -a /dev/sda

If Reallocated Sectors Count or Pending Sectors is high, it’s a sign of a failing disk.

🛠️ 3. Fixing the Read-only Filesystem Issue

Once you've identified the cause, follow the appropriate solution below.

🔹 Case 1: Remount the Filesystem in Read-Write Mode

If the system was accidentally mounted as read-only, remount it as read-write:

mount -o remount,rw /

✅ Test by creating a new file:

touch /testfile

📌 If this works, the issue was temporary, and no further action is needed.

🔹 Case 2: Fix Filesystem Errors with fsck

If your filesystem is corrupted, follow these steps:

1️⃣ Boot into Recovery Mode or a Live CD If / is mounted as read-only, unmount the partition before repairing:

umount /dev/sda1

2️⃣ Run fsck to Check and Repair the Filesystem

fsck -y /dev/sda1

📌 The -y option automatically fixes errors.

3️⃣ Reboot the system

reboot

✅ If errors were fixed, the filesystem should now mount as read-write.

🔹 Case 3: Fix /etc/fstab Misconfiguration

If the issue is caused by an incorrect /etc/fstab entry, follow these steps:

1️⃣ Check /etc/fstab

cat /etc/fstab

📌 Example Incorrect Entry:

UUID=abc123 / ext4 defaults,ro 0 1

❌ The "ro" option forces read-only mode!

2️⃣ Fix the Configuration Edit /etc/fstab:

nano /etc/fstab

Change:

UUID=abc123 / ext4 defaults,rw 0 1

✅ Save the file and reboot:

reboot

🔹 Case 4: Disk Failure – Backup & Replace the Drive

If smartctl reports a failing disk, it's time to back up data and replace the drive.

1️⃣ Copy Data to a Backup Drive Use rsync to back up important files:

rsync -av /home/ /mnt/backup/

2️⃣ Clone the Disk (If Still Readable)

dd if=/dev/sda of=/dev/sdb bs=64K conv=noerror,sync

3️⃣ Replace the Hard Drive Once backed up, install a new disk, reinstall Linux, and restore your data.

🛡️ 4. Preventing Future Read-only Filesystem Issues

Follow these best practices to avoid this problem in the future:

✅ Use a UPS (Uninterruptible Power Supply) to prevent power-related filesystem corruption.
✅ Run regular disk health checks:

smartctl -a /dev/sda

✅ Schedule periodic filesystem checks:

fsck -n /dev/sda1

✅ Modify /etc/fstab safely – Always back it up before making changes:

cp /etc/fstab /etc/fstab.bak

📊 5. Summary

💬 Join the Discussion!

Have you ever encountered the "Read-only file system" error in Linux?
What steps did you take to resolve it?

💬 Share your experience in the comments below! 🚀

👉 If you’re troubleshooting Linux boot issues, check out: How to Fix GRUB Boot Failure in Linux