How to fix "sudo: unable to open ... Read-only file system"?

If you have the graphical user interface go to the disk application, select the drive with the issue, click on the gears icon and choose the option Repair Filesystem. In less than a second the problem is fixed.

I have had this problem on my computer for over 1 year and tried everything to solve the problem. Suddenly Linux goes into read-only mode. If you are editing something you are unable to save and have to execute fsck command and reset the computer. The computer is also very slow and freezing all the time. I removed the dual boot and left only Ubuntu, upgraded Ubuntu from version 18.04 LTS to version 20.04 LTS, and it didn't work. What was crucial to solving the problem is the use of the dmesg command. The experience didn't work out for me, just this command. The function of this command is to monitor the computer.

In my case, the problem was related to the SSD incompatibility with Ubuntu. I used HDD and after I switched to SSD the problem came up. The problem was solved by updating the SSD firmware, which was only possible by partitioned Windowns, because Kingston does not have the program to update firmware through Linux. I also installed the dual boot Windowns and Linux, first installing Windows over the entire SSD, then deallocating space through Windowns and installing Ubuntu, but it is very unlikely that this was the solution to the problem.

If you dual boot ubuntu alongside windows 10 it's probably windows 10's fast start-up that's holding onto your filesystem , it doesnt unmount your hard disks properly. to fix this you need to boot into windows 10

1. Start > Power Settings
2. click on Additional power setting on the right
3. click on choose what thepower buttons do on the left
4. clock on change settings that are currently unavailable
5. unmark turn on fast-startup
6. save changes and then reboot into ubuntu everything will work fine!

It looks like some mounted files have got corrupted, and as a result, the kernel has set the file system to RO to prevent further damage. To find which file system is corrupted, we could run:

cat /proc/mounts | grep -i ro

The output would be similar to the below:

proc /proc proc rw,nosuid,nodev,noexec,relatime 0 0
/dev/sda1 / ext4 ro,relatime,data=ordered 0 0
tmpfs /sys/fs/cgroup tmpfs ro,nosuid,nodev,noexec,mode=755 0 0

One of the solutions for this issue could be to remount the corrupted file system.

If you were in situations that can not use live disc, e.g. you are remotely ssh into your system, you can still using the command that @Bibhas had answered:

sudo fsck.ext4 -f /current/filesystem/mount/point

It will prompt for fixing your filesystem error. You also need to reboot your system remotely.

I am using the 18.04 LTS release and what I did was, first I unmounted my damaged drives then I went into “Disks” app by seaching in the dash. From there I selected the drive which was damaged. Make sure it is unmounted else it won’t work. In the options menu (the little gear shape), and clicked on “repair file system”. Boom! Worked like a charm.

If you're dual booting your machine with Ubuntu and Windows together and this issue occurs,it's because Windows changes the filesystem,in that case this might do the trick. Try disabling fast startup

Control Panel > Hardware and Sounds > Power Options > (in the left) Choose what closing the lid does > Change settings that are currently unavailable > Untick 'Turn on fast startup'

Now booting into Ubuntu will solve the issue. Hope this helps!

https://youtu.be/KJ-0KPZhAFo

(Deleted previous answer)

Edit: The main problem was on the windows side. After updating my Windows 10, the 'quick start' option automatically got enabled. On disabling that option again, and then again re-starting the machine, the problem went away. Windows 10 gave me heavy headache for days :(

The 'quick start' option can be found in 'power options' in the control panel. Disable that!!! :)

Check if you have any faulty hardware.I got this error due to a hardisk loosening. Ran mount -o remount,rw / and it worked fine.

For me,Rebooting a system solving this issue

sudo reboot

as he mentioned about it.

Remember

as System Administrator rebooting should be the latest Solution

It's misconfigured boot settings (try mounting / as ext2) not drive or partition physical error.

dmesg | grep "error" gave me:

ext3-fs (sda2): error: couldn't mount because of unsupported optional features (240) 
ext2-fs (sda1): error: couldn't mount because of unsupported optional features (240) 
ext4-fs (sda2): mounted file system with ordered data mode: opts: (null)

It mounted / as read only due to the fstab error=mount-ro directive.

Note that sometimes this can be caused by the computer forgetting the system time - disk check fails because the dates in the journal are in THE FUTURE!

Setting the BIOS time (and checking the BIOS battery) fixed this problem for me, without having to do any disk recovery.

In my case it was down to RAID 1 stabilizing after the initial installation. I have /boot and / on s/w RAID1. Having left the system overnight and rebooted, everything is working fine. Richard

If you want to force your root filesystem to remount as rw, you can do the following.

mount -o remount,rw /

The answer by hexafraction didn't work for me. Every time I tried executing sudo fsck -Af -M it just showed

$ sudo fsck -Af -M
fsck from util-linux 2.20.1

and nothing else. No error or anything. For me, booting into a live disc and executing this worked -

sudo fsck.ext4 -f /dev/sda1

Provided the partition in question /dev/sda1 was an ext4 filesystem.

Try running dmesg | grep "EXT4-fs error" to see if you have any issues related to the filesystem / journaling system itself. I would recommend you to restart your system, then. Also, sudo fsck -Af answer by ObsessiveSSOℲ won't hurt.

Here is the command that solved my problem :

mount -o remount /

better than a reboot or sudo fsck -Af

The filesystem will usually go into read-only while the system is running if there is a filesystem consistency issue. This is specified in fstab as errors=remount-ro and will occur when a FS access fails or an emergency read-only remount is requested via Alt+SysRq+U. You can run:

sudo fsck -Af -M

to force a check of all filesystems. As one of the other answers states, looking at dmesg is also very helpful.

Edit: Don't forget the -M on the command-line.

NOTE: As mentioned by Bibhas in his answer: If fsck gets stuck after its version banner:

$ sudo fsck -Af -M
fsck from util-linux 2.20.1

you may want to try using the EXT4-specific fsck

$ sudo fsck.ext4 -f /dev/sda1

Provided the partition in question /dev/sda1 was an ext4 filesystem.

Usually linux puts your filesystems in read only when errors occur, especially errors with the disk or the filesystem itself, errors like a wrong journal entry for example.

You better check your dmesg for disk related errors.

Google is full of discussion about this and you can pick the ones that is closer to your configuration, but a look at dmesg is usually enough.