What does this do?

`man chattr` says:

"A file with the `a' attribute set can only be open in append mode for writing. Only the superuser or a process possessing the CAP_LINUX_IMMUTABLE capability can set or clear this attribute."

After some experimentation, it makes a file impossible to delete.

Very clever, +1.

I wonder if this solves the issue of multiple bash instances clobbering history.

From the bash manpage:

    If the histappend shell option  is  enabled (see  the description of shopt
    under SHELL BUILTIN COMMANDS below), the lines are appended to the history
    file, otherwise the history  file  is overwritten.


    histappend
        If  set,  the history list is appended to the file named
        by the value of the HISTFILE  variable  when  the  shell
        exits, rather than overwriting the file.

http://askubuntu.com/a/80380/288724 looks like it might be my issue, specifically

> The bash session that is saved is the one for the terminal that is closed the latest.

I always seem to get this wrong or forget to set it up in my bashrc. I'll add it to my dotfiles repo, thanks.

unset HISTFILE