A fast and comfortable solution to use multiple Linux installations at once without permanent reboots:
/etc/fstab:
/dev/XXX / ext3 defaults ...
/dev/XXX /mnt/Testing ext3 defaults ...
/dev/XXX /mnt/Unstable ext3 defaults ...
/dev/XXX /mnt/Gentoo ext3 defaults ...
tmpfs /tmp tmpfs defaults ...
/tmp /mnt/Gentoo none bind 0 0
/tmp /mnt/Testing none bind 0 0
/tmp /mnt/Unstable none bind 0 0
proc /proc proc defaults 0 0
proc /mnt/Testing/proc proc defaults 0 0
proc /mnt/Unstable/proc proc defaults 0 0
proc /mnt/Gentoo/proc proc defaults 0 0
devfs /mnt/Testing/dev devfs defaults 0 0
devfs /mnt/Unstable/dev devfs defaults 0 0
devfs /mnt/Gentoo/dev devfs defaults 0 0
pts /dev/pts devpts defaults 0 0
pts /mnt/Testing/dev/pts devpts defaults 0 0
pts /mnt/Unstable/dev/pts devpts defaults 0 0
pts /mnt/Gentoo/dev/pts devpts defaults 0 0
Now as root user
chroot /mnt/Testing
or use
dchroot:
/etc/dchroot.conf
testing /mnt/Testing/
gentoo /mnt/Gentoo/
unstable /mnt/Unstable/
And now:
dchroot -c unstable -d