Under Gentoo, it's not possible to unmount the /usr filesystem. The reason is,
that bash always uses the following files in /usr, keeping the filesystem busy:
/usr/lib/gconv/ISO8859-15.so (or similiar)
All these files are part of glibc. While /usr/lib/gconv has a size of ~4.5M and
could easily fit in the root filesystem, locale-archive is over 18M in size.
It seems, that bash doesn't need gconv to run, since it works when I remove /usr
from fstab and reboot with the "single" option.
Steps to Reproduce:
1.You need to have /usr on a separate partition/device
2. Switch to single user mode
3. try to umount /usr
umount: /usr: device is busy
/usr should have been unmounted
Use sash ?
Another alternative might be to compile bash without nls support. I
however do not know if this is an idea that will be appreciated by all
Moving /usr/lib/gconf is not a good idea i think.