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Saturday, December 26, 2009

Recouping your data from a hung program

Scenario: you are typing away in your blog editor on Ubuntu doing a (somewhat) Flash-heavy post. You make the mistake of hitting "Preview" and the blogging software hangs. How can you get your post out?

  1. Find the PID of your blogging software
  2. Coredump it (gcore [PID] - this will create a file called core.[PID] in the current directory) - sidenote: interestingly, coredumping doesn't actually kill the application - this makes me wonder about thread safety... What guarantees does gcore make about the consistency of the dumped state? Probably none... This isn't important in this case, since the program is hung for good.
  3. Use a hex editor (GHex for example) and search for a part of the blogpost. You will probably find it multiple times, but you can easily identify one occurrence which has a complete copy.
  4. Copy the blogpost from the hexeditor
  5. Profit!

Hope this saves somebody from retyping their text!

PS. This can be applied to other programs too where the storage format is "human readable" (like text editors - as opposed to spreadsheet editors). An other trick you might try is to search for the string as Unicode (since more international-aware programs might store it as that). While GHex doesn't support this directly, you can manually insert the 00 bytes between the Latin characters. An other option would be to run strings on the coredump file with different --encoding options.


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