Bash loses all my history on occasion.  This will eventually happen to everyone who runs multiple bash sessions, eg:

  http://superuser.com/questions/20900/bash-history-loss

The problem occurs when multiple instances exit simultaneously.  One example is when you close a multi tab xterm.

It happens when bash is enforcing HISTFILESIZE.  Bash re-reads the history, then truncates the file, then the smaller fine.  If several bash instances are doing this as the same time there is a race condition.  It's possible for one bash instance to read .bash_history between when it is truncated and when it is written, and thus it sees a zero length file.  If the last version of .bash_history is this 0 length version all history is lost.

The attached patch works around the problem by writing the new version to a temporary file, then renaming it.  Since POSIX guarantees rename() is atomic the race is gone.