Fix "mount: unknown filesystem type" (ntfs, exfat, LVM2_member, crypto_LUKS)

lsblk -f

What the error means

$ sudo mount /dev/sdb1 /mnt
mount: /mnt: unknown filesystem type 'LVM2_member'.

mount identified the content of the partition (via blkid) or you passed -t, and the kernel has no driver registered under that name. That happens for two different reasons:

• The type is a real file system whose driver is missing or cannot load (ntfs, exfat, apfs, zfs).
• The type is not a file system at all but a container layer (LVM2_member, crypto_LUKS, linux_raid_member, zfs_member, bcache). You open the layer first and mount what is inside.

Check what you are dealing with:

lsblk -f
sudo blkid /dev/sdb1

Example output:

NAME          FSTYPE      FSVER    LABEL UUID
sdb
├─sdb1        vfat        FAT32          8A1C-3F02
└─sdb2        crypto_LUKS 2              b7e4...
  └─luks-b7e4 LVM2_member LVM2 001       Qx2P...
    ├─vg-root ext4        1.0            51ad...
    └─vg-swap swap        1              9c0e...

This layout (LUKS containing LVM containing ext4) is exactly what Ubuntu's and Fedora's "encrypt the disk" install options create.

Cause 1: the kernel was updated and you have not rebooted

If mounting this type worked before, check this first. Package managers remove the old kernel's modules directory during an upgrade. The running kernel then cannot load drivers that were not already loaded, such as exfat, ntfs3 or vfat.

uname -r
ls /lib/modules/

If the version from uname -r is not listed in /lib/modules/, reboot. This is especially common on Arch and openSUSE Tumbleweed.

Cause 2: NTFS

Linux 5.15 and later include the ntfs3 read-write driver. Ask for it by name:

sudo mount -t ntfs3 /dev/sdb1 /mnt

If you prefer -t ntfs or want the repair tool ntfsfix, install ntfs-3g, which provides the mount.ntfs helper:

If NTFS then fails with "wrong fs type" and "volume is dirty", Windows Fast Startup left it unclean: see the NTFS and exFAT mounting guide.

Cause 3: exFAT

exFAT support has been in the kernel since 5.7, so on current distros this error almost always means the module is missing from your kernel package (cause 1, or a minimal kernel; see the notes below). exfatprogs provides mkfs.exfat and fsck.exfat. The old FUSE package exfat-fuse is no longer needed. Check the module:

sudo modprobe exfat && echo loaded

Cause 4: LVM2_member

The partition is an LVM physical volume. Typical when you plug in a disk from another Linux machine or mount from a live USB.

sudo apt install lvm2        # or dnf / pacman / zypper install lvm2, if missing
sudo vgscan
sudo vgchange -ay
sudo lvs

Example output:

  LV   VG        Attr       LSize
  root ubuntu-vg -wi-a----- 100.00g

sudo mount /dev/ubuntu-vg/root /mnt

If both your running system and the plugged-in disk use the same volume group name (two Ubuntu installs both called ubuntu-vg), LVM shows a duplicate. Rename the foreign one by its UUID from sudo vgs -o vg_name,vg_uuid: sudo vgrename <UUID> oldvg. Renaming a volume group that a system boots from requires updating its fstab and GRUB, so only rename the disk you are rescuing data from, and rename it back before booting it again.

When you are done: sudo umount /mnt and sudo vgchange -an ubuntu-vg before unplugging.

Cause 5: crypto_LUKS

The partition is encrypted with LUKS. Unlock it to get a decrypted device under /dev/mapper:

sudo cryptsetup open /dev/sdb2 data
lsblk -f /dev/mapper/data
sudo mount /dev/mapper/data /mnt

If lsblk shows the unlocked device as LVM2_member, continue with cause 4. Close it afterwards with sudo umount /mnt then sudo cryptsetup close data. Desktop file managers do the same thing when you click the drive and enter the passphrase. Install cryptsetup if the command is missing.

Cause 6: RAID, ZFS and other layers or formats

Distro-specific notes

• Ubuntu: cloud, virtual and some minimal installs use a kernel flavour with fewer modules. Install the extras for the running kernel: sudo apt install linux-modules-extra-$(uname -r).
• Debian, Mint: install lvm2 and cryptsetup on a live system if they are missing; the official live images include them.
• Fedora: some rarely used file system modules are packaged separately in kernel-modules-extra: sudo dnf install kernel-modules-extra, then reboot if the kernel was updated at the same time.
• Arch: after pacman -Syu upgrades linux, reboot before mounting new types (cause 1).
• openSUSE: rarely used modules may live in kernel-default-extra; Tumbleweed has the same reboot-after-update issue as Arch.

How to prevent it

• Reboot soon after kernel updates.
• Keep ntfs-3g, exfatprogs, lvm2 and cryptsetup installed on rescue USBs.
• Write down the layout (lsblk -f) of encrypted/LVM disks so you know which layers to open. The disk management guide explains partitions, LVM and fstab.
• If the type is a normal file system but mounting fails with "bad superblock", see wrong fs type, bad superblock.

Frequently asked questions