how to un-shoot your foot 9

Posted by peter on September 29, 2008

Recently I shot myself in the foot pretty bad. We have a ~12TB data array that was set up as a raw LVM2 device- no partition table. There were some issues with one of the cluster members, so I went to rescue boot to attempt to correct it. Redhat’s rescue boot, in the name of spreading democracy, proactively offers to put a partition table on anything that doesn’t have one already, and I fat-fingered the key that made this happen right over the top of our array. Whoops.

This isn’t impossible to recover from- the only thing that got overwritten was, for the most part, LVM data, and it so happens that the boundaries of the volumes is more or less known (25% each), so recovery should be possible just by re-writing correct (or near-correct) headers setting the boundaries in the right spot. Problem with this approach is that you get one shot, and it’s not like we have another 12TB sitting around that we can copy the data to. Here’s where dm-mapper came in to save my ass.
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apple’s dirty little python secret

Posted by peter on July 29, 2008

From man python on OS X 10.5 (and probably before):

INTERACTIVE INPUT EDITING AND HISTORY SUBSTITUTION
       The Python inteterpreter supports editing of the current input line and
       history substitution, similar to facilities found in the Korn shell and
       the  GNU  Bash shell.  However, rather than being implemented using the
       GNU Readline library, this Python interpreter  uses  the BSD  EditLine
       library editline(3) with a GNU Readline emulation layer.


       The  readline  module  provides the access to the EditLine library, but
       there are a few major differences compared to a traditional implementa-
       tion  using  the  Readline  library.   The command language used in the
       preference files is that of EditLine, as described in editrc(5) and not
       that   used  by  the  Readline  library. This  also  means that  the
       parse_and_bind() routines uses EditLine commands.  And  the preference
       file itself is ~/.editrc instead of ~/.inputrc.


       For  example,  the rlcompleter module, which defines a completion func-
       tion for the  readline  modules,  works correctly  with the  EditLine
       libraries, but needs to be initialized somewhat differently:


              import rlcompleter
              import readline
              readline.parse_and_bind ("bind ^I rl_complete")


       For vi mode, one needs:


              readline.parse_and_bind ("bind -v")

Well, that explains why Python doesn’t play nice with my readline stuff.