mount: wrong fs type, bad option, bad superblock on /dev/sdX, missing codepage or helper program

What the message looks like

$ sudo mount /dev/sdb1 /mnt/data
mount: /mnt/data: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error.

Common causes

• The helper for this filesystem is missing: nfs-common for NFS, cifs-utils for SMB, ntfs-3g or exfatprogs for NTFS and exFAT.
• The device has no filesystem yet, or a different type than you gave, or you mounted the disk instead of its partition.
• A bad option or a typo in /etc/fstab.
• The filesystem is damaged or was not shut down cleanly.
• The device name changed after a reboot, so the line points to the wrong disk.

Check

1. What does the device contain?
   lsblk -fCopy
2. Why did the kernel refuse? Read the last lines
   journalctl -k -n 20 --no-pagerCopy
3. Type and UUID of the partition
   sudo blkid /dev/sdb1Copy
4. Does fstab look valid?
   findmnt --verifyCopy

Fix

• Read the kernel log first, it often says the exact reason.
• Install the missing helper for the filesystem and mount again, for example sudo apt install nfs-common, cifs-utils or ntfs-3g.
• Mount the right device with the right type: sudo mount -t ext4 /dev/sdb1 /mnt/data. In fstab use UUID= instead of /dev/sdX, then test with sudo mount -a.
• If it looks damaged, check it read-only first while unmounted: sudo fsck -n /dev/sdb1. Repair with fsck only after a backup. A repair can change or remove data.
• If blkid shows nothing, the disk has no filesystem. Creating one with mkfs erases everything on it. Do it only on a disk you are sure is empty.

FAQ

Is my data gone?

Not necessarily. The message is generic. Do not run mkfs or a repair before you know the cause and have a copy, for example an image made with dd on another disk.

Why does it fail only at boot?

A wrong line in /etc/fstab or a disk that is not ready. Add nofail for non-essential disks so the boot does not stop.