This is a tutorial / fan post for Slicehost’s Rescue Mode. Rescue Mode saved me from my own stupid mistakes and also a known Gentoo bug.
While fiddling around in my /etc/fstab file (added “data=writeback” to the mount options), I rendered my Gentoo VPS unbootable. Oh well, I just need to boot a LiveCD and fix my stupid fstab. Wait, this isn’t a physical Gentoo box in front of me, but a virtual server hosted miles away from me…
Ta da, Slicehost’s Rescue Mode to the, uhh, rescue. I log into SliceManager, go to the Rescue panel of my slice, and click “Enter Rescue Mode”. SliceManager gives me a temporary root password, and finishes building the Rescue Slice in a few minutes. Instant LiveCD-like rescue environment!
To fix my fstab, I SSH into my Rescue Slice with the temporary root password. The partition holding my regular slice is available as /dev/sda1 (and my swap partition is /dev/sda2 if I need that for some reason). I mount my regular slice,
mkdir /mnt/slice
mount /dev/sda1 /mnt/slice
fix my fstab file,
nano /mnt/slice/etc/fstab
and finally return to SliceManager and click “Exit Rescue Mode”. Problem solved. Slicehost’s Rescue Mode rocks!
Unfortunately, my VPS failed to boot again but with a different error. It died upon trying to mount /proc.
The "mount" command failed with error: proc already mounted
It turns out this is a known Gentoo bug when working with Xen. Apparently Gentoo Xen guests should not try to mount /proc and /sys. I don’t understand what triggered this problem or why I did not encounter it before.
So back I go into Rescue Mode to fix this by commenting out the section of /sbin/rc that attempts to mount /proc and /sys (if you only skip /proc mounting, the next bootup will die trying to mount /sys).
mkdir /mnt/slice
mount /dev/sda1 /mnt/slice
nano /mnt/slice/sbin/rc
Around line 217, comment out these chunks of code like so: (source)
# check_statedir /proc
#
# ebegin "Mounting proc at /proc"
# if [[ ${RC_USE_FSTAB} = "yes" ]] ; then
# mntcmd=$(get_mount_fstab /proc)
# else
# unset mntcmd
# fi
# try mount -n ${mntcmd:--t proc proc /proc -o noexec,nosuid,nodev}
# eend $?and a few lines later:
# if [ "$(get_KV)" -ge "$(KV_to_int '2.6.0')" ] ; then
# if [[ -d /sys ]] ; then
# ebegin "Mounting sysfs at /sys"
# if [[ ${RC_USE_FSTAB} = "yes" ]] ; then
# mntcmd=$(get_mount_fstab /sys)
# else
# unset mntcmd
# fi
# try mount -n ${mntcmd:--t sysfs sysfs /sys -o noexec,nosuid,nodev}
# eend $?
# else
# ewarn "No /sys to mount sysfs needed in 2.6 and later kernels!"
# fi
# fiThat’s it. Happy rescuing. 
