I feel awful...
I was trying to install picasa, but my /opt wasn't large enough. There was no logical volume for it like most of my other partitions (default debian etch lvm non-encrypted scheme w/ home, var, and others on lvm).
First I did
lvreduce -L1G /dev/<lvgname>/var
to reduce the var by 500 megs since it was not using anywhere near that much.
Next I did
lvcreate -L500M /dev/<lvgname>/opt
to make a logical volume for opt.
After that I put
/dev/mapper/<lvname>-opt /opt ext3 defaults 0 2
in /etc/fstab to follow the forms of the similar lvm entries.
So now I can boot, but everything's borked. I can ping google, for instance, but I can't use apt-get install. X11 won't start up, but I can use vim. If I comment out the line for opt in fstab, it still doesn't work. I noticed a lot of errors at boot about read-only directories, so I think my lvm's were mounted read-only. I'm pretty ignorant about this obviously...
Also, at boot, when it tries to do fsck.ext3 on var, it fails. I think /var is the only thing that ends up being read-only during boot. Of course this botches a lot of things since syslog hangs and other things don't work. But all the data seems to be there just fine, I just don't know how to get my system back to where it was.
Is there anything I can do?