[RndTbl] boot / fsck debug shells

Trevor Cordes trevor at tecnopolis.ca
Wed Dec 14 02:34:41 CST 2011

Further to Gilbert's debug shell keyboard issues:

I've been dealing with lots of md upgrade problems lately and non-boot 
scenarios.  Not sure if you're seeing the same thing, but what's worked 
great for me is boot with kernel args: rdshell rddebug.  Don't use the 
sushell or whatever it was you were mentioning as that forces your login.

When the system can't boot due to md / fsck it will drop you in a rdshell 
(real crap shell) without any pw prompt.  From there you can run mdadm 
commands, and probably fsck, to get your system bootable.  In fact, once 
you get your / fs alive you can mount it to /sysroot and type "exit" and 
the system will boot as normal!

Once in the live system you can run "dracut" (possibly with --force) to 
create a fixed/bootable rd.  Assuming that's your problem.

I've used this TONS lately when upgrading linux boxes from non-raid to md 
raid or small disks (raid) to bigger disks (raid).  Any situation where 
your drive labels/uuids/majors/minors change can fark up your booting.  
This lets you fix it (without OS reinstall).

Had a horrible time just this last week where I had booting md complain 
that sda3 and sda shared a md superblock and it wouldn't boot.  Even with 
the above tools, I couldn't get it to boot without manual rdshell 
intervention until I revamped the whole disk so that there was a tiny bit 
of space at the very end of the disk, so sda had its own tiny area at the 
end (and I zeroed its superblock).

Anyhow, just thought perhaps there may be some overlap in problems and I 
could save you some headache.

Linux: the (nearly) only OS you can always fix and never need to reinstall 
(upgrade or wipe/install).  Love it!

(Note to others, this stuff may be RH/Fedora specific as I have no idea if 
other distros use dracut or provide rdshell.)

More information about the Roundtable mailing list