External disk with ext4 doesn’t auto-mount

I have an external SSD in a NVME USB enclosure, with an EXT4 file-system. When I plug it in, it doesn’t auto-mount, and haven’t done so for a while.

Most other external disks do auto-mount.

I finally figured out why, and how to fix it.

There’s a default UDEV rule in /usr/lib/udev/rules.d/64-ext4.rules:

SUBSYSTEM=="block", ENV{ID_FS_TYPE}=="ext2|ext3|ext4|ext4dev|jbd", ENV{UDISKS_AUTO}="0"

Change the final “0” to a “1” and reload the udev rules, and the disks auto-mount.

If you don’t want to overwrite a system file, save it as /etc/udev/rules.d/64-ext4.rules.

To reload udev without rebooting, use this command:

udevadm control --reload-rules && udevadm trigger

Plug in your disk, and it’ll mount automatically. Finally!