mount: unknown filesystem type

This document (000020327) is provided subject to the disclaimer at the end of this document.

Environment

SUSE Linux Enterprise Server 15
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 11

Situation

When trying to mount a disk, the system reports the following error:

s12sp4:~ # mount /dev/vg01/vfatLV /mnt
mount: unknown filesystem type 'vfat'

This could apply to other filesystem types as well. vfat was taken as an example.

Resolution

To fix the issue:

Reinstall the kernel and make sure the kernel drivers are installed
Check the modprobe configuration for the driver. Reference: man modprobe.d

Cause

The problem could be caused by multiple reasons, here are two causes of such issue:

1. The kernel driver for this filesystem type is missing. In this case vfat.ko.
modinfo command can be used to check if the kernel driver is installed.
Kernel modules are normally stored in: /lib/modules/`uname -r`
2. The kernel driver exists but could not be loaded.
modprobe -v -n command could be used to test loading the kernel driver.

Additional Information

Two ways to simulate the issue:

Method 1. Move or rename the driver.

s12sp4:~ # old /lib/modules/4.12.14-95.54-default/kernel/fs/fat/vfat.ko
s12sp4:~ # ll /lib/modules/4.12.14-95.54-default/kernel/fs/fat/vfat.ko*
-rw-r--r-- 1 root root 29056 Jun  5  2020 /lib/modules/4.12.14-95.54-default/kernel/fs/fat/vfat.ko-20210709
s12sp4:~ # mount /dev/vg01/vfatLV /mnt
mount: unknown filesystem type 'vfat'

Method 2. Wrong modprobe configuration. E.g. here we tell modprobe to run /bin/true instead of inserting the module in the kernel as normal.

s12sp4:~ # lsmod | grep fat
s12sp4:~ # echo 'install vfat /bin/true' > /etc/modprobe.d/99-block-vfat.conf
s12sp4:~ # modprobe -v -n vfat
insmod /lib/modules/4.12.14-95.54-default/kernel/fs/fat/fat.ko
install /bin/true
s12sp4:~ # mount /dev/vg01/vfatLV /mnt
mount: unknown filesystem type 'vfat'
s12sp4:~ # modprobe -v -n vfat
install /bin/true
s12sp4:~ # rm /etc/modprobe.d/99-block-vfat.conf
s12sp4:~ # modprobe -v -n vfat
insmod /lib/modules/4.12.14-95.54-default/kernel/fs/fat/vfat.ko
s12sp4:~ # mount /dev/vg01/vfatLV /mnt
s12sp4:~ # df -hT /mnt
Filesystem              Type  Size  Used Avail Use% Mounted on
/dev/mapper/vg01-vfatLV vfat   52M     0   52M   0% /mnt

Disclaimer

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