Chapter 9 Device Busy

While trying to unmount the lfs partition, using: umount -v $LFS, I get device busy warnings.
Here is an example of how I debugged this, thanks to Holy Scmoly
Note that I have already logged out of the chroot environment.

[root~]# fuser -m /dev/sdb6

/dev/sdb6:            3184c

[root~]# ps auxw | grep  3184

root      3184  0.0  0.1   4024  1820 pts/0    S+   08:25   0:00 bash

root     32081  0.0  0.0   3224   744 pts/1    S+   10:36   0:00 grep --color 3184

[root@samwise ~]# kill -9 3184

Clearly, that bash is from the exec command I used and am not sure was necessary. Re-run the fuser command and it should be ok.
[root@ ~]# umount -v $LFS
/dev/sdb6 umounted