Implications of nix on challenge images

[ConnorNelson]

Here I will document interesting non-immediately-obvious effects of nix as they are discovered.

• GDB symbols (Fix GDB Symbols #467). The default nix version of gdb does not check /lib/debug for symbols (e.g. what is the return type of __libc_start_main?). This can be resolved in gdb with set debug-file-directory /lib/debug. Issue still open to make this non-manual.

• Man page indexes (pwncollege/linux-luminarium@dcaec9f). Ubuntu uses GNU gdbm (index.db) while nix uses Berkeley db (index.bt). This means that the index for /usr/share/man present in /var/cache/man/index.db will not be searched by the nix man -k.