mount: wrong fs type, bad option, bad superblock on /dev/sdb1
mount gives this one generic message for several unrelated failures, and the real reason is only in the kernel log. For NFS or CIFS it nearly always means the helper package (nfs-common or cifs-utils) is not installed. For a block device it is usually a disk that was never formatted, the wrong -t type, or a mount option the filesystem does not support.
Quick fix
Read the commands before running them. Anything that restarts a service, deletes data or changes permissions should be tried on a non-production system first.
# The kernel says what actually went wrong
sudo dmesg | tail -20
# What filesystem, if any, is on the device?
lsblk -f /dev/sdb
sudo blkid /dev/sdb1
# Network shares need their helpers
sudo apt install nfs-common cifs-utils
ls /sbin/mount.*
# Brand new disk with no filesystem (this ERASES the partition)
# sudo mkfs.ext4 /dev/sdb1
# Check a damaged ext4 filesystem, unmounted
sudo fsck -n /dev/sdb1How to diagnose Storage errors
Storage errors are dominated by permissions and locality. S3 access denials can come from an IAM policy, a bucket policy, a Block Public Access setting, an ACL or a KMS key policy: five independent layers, all of which must allow the call. Block storage errors are usually about availability zones: a volume can only attach to an instance in the same AZ.
If the quick fix above does not resolve it, work through these steps. They apply to this whole class of error, not just to this one message, which is usually what saves the time.
- For S3 denials, check all five layers: IAM policy, bucket policy, Block Public Access, object ACL and the KMS key policy if the object is encrypted with a customer-managed key.
- Confirm the region and the exact bucket name. A bucket in another region returns a redirect or a permanent error that reads like a permission problem.
- For signed URLs, check the expiry and that the clock on the signing machine is correct. A skewed clock produces URLs that are already expired.
- For NFS stale file handles, remount rather than retrying; the file the handle referred to no longer exists on the server.
- For volume attachment failures, verify the availability zone matches and that the volume is in the
availablestate, not still attached elsewhere.
Tools worth reaching for
aws s3api get-bucket-policyIAM Policy Simulatormount -v / showmount -edf -h / du -shaws ec2 describe-volumes
Authoritative references
Primary documentation for this error, worth reading before applying any fix in production.
Related Storage errors
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Something missing or wrong?
This entry is maintained by hand. If the fix is out of date, incomplete, or you have a better one, email a correction and it will be reviewed.