BtrFS

ZFS

Utilities

mount – mount a filesystem

mount -t type device dir

mount --bind olddir newdir

chroot – run command or interactive shell with special root directory

Run COMMAND with root directory set to NEWROOT.

Tasks

use chroot

Mount your drives

mount -t ext4 UUID=ABCD-1234 /my/mount/point
mount -t vfat UUID=ABCD-1235 /my/mount/point/boot

Mount other stuff

mount -t proc /proc /my/mount/point/proc
mount -t sysfs /sys /my/mount/point/sys
mount --bind /dev /my/mount/point/dev
mount --bind /dev/pts /my/mount/point/dev/pts

Dive in

chroot /my/mount/point

umount problems

shit is in use

lsof +D /path

fuser -km /mnt/share

Also, check that the filesystem is not shared (NFS,SMB…)