Mount ext4 disk: cannot mount /dev/sdc read-only

ext4mount

I have an SSD disk with an ext4 filesystem on it:

$ lsblk -f /dev/sdc 
NAME FSTYPE LABEL UUID                                 MOUNTPOINT
sdc  ext4         142b28fd-c886-4182-892d-67fdc34b522a

I am attempting to mount it, but it is failing:

$ sudo mkdir /mnt/data
$ sudo mount /dev/sdc /mnt/data
mount: /mnt/data: cannot mount /dev/sdc read-only.
  • What does the error message mean?
  • How can I diagnose and fix the problem?

To add additional information pertinent to an answer below:

There is only one partition on the disk.

Here is the result of executing lsblk for the boot disk:

$ lsblk /dev/sda
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda       8:0    0   10G  0 disk 
├─sda1    8:1    0  9.9G  0 part /
├─sda14   8:14   0    4M  0 part 
└─sda15   8:15   0  106M  0 part /boot/efi

and here is the result of executing lsblk for the disk in question:

$ lsblk /dev/sdc
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sdc    8:32   0   2G  1 disk

Best Answer

I had a similar problem with a USB thumb drive which was down to the ext4 journal recovery not working. dmesg confirmed this:

[1455125.992721] EXT4-fs (sdh1): INFO: recovery required on readonly filesystem
[1455125.992725] EXT4-fs (sdh1): write access unavailable, cannot proceed (try mounting with noload)

As it suggested, mounting with noload worked:

sudo mount -o ro,noload /dev/sdh1 /mnt/drive

I was then able to backup the content:

sudo rsync -av /mnt/drive /data/tmp/

and then use fdisk to delete and recreate the partition and then create a new filesystem with mkfs.ext4.

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