Linux distributions for the x86_64 platform have different approaches when it comes to the installation of 32-bit and 64-bit libraries. In a 64-bit platform, 64-bit libraries are required to run all the standard applications but 32-bit libraries need to be available to provide compatibility with 32-bit binaries. In this post, I consider 64-bit applications to be the native ones and the 32-bit to be foreign.

The two major approaches I have seen are:

• lib32 and lib64 directories, leaving lib to be just a symbolic link to the directory required by the native applications. This is the approach followed by Debian. The advantage of this layout is that the lib directory is the correct one for native applications. However, foreign applications that have built-in paths to lib, if these exist, will fail to work.
• lib and lib64 directories. This is the approach followed by Fedora. In this layout, the foreign applications which have built-in paths to lib will work just fine, but the native applications have to be configured explicitly to load libraries and plugins from within lib64.

I have found so far two instances where the Fedora approach fails because native 64-bit applications hardcode the lib name in some places, instead of using lib64. One of these were the NetworkManager configuration files, which had an incorrect setup for the OpenVPN plugin and it failed to work. This issue has already been fixed in Fedora 9. The other problem was in gnome-compiz-manager where the application tries to load plugins from the lib directory, but as it is a 64-bit binary, it failed due to a bitness mismatch. This has been reported but is not yet fixed upstream. I'm sure several other similar problems remain to be discovered.

I personally think that the Debian approach is more appropriate because it seems weird that all standard system directories, such as bin or libexec, contain 64-bit binaries but just one of them, lib, is 32-bit specific.

As a side note, NetBSD follows an slightly different approach: lib contains 64-bit libraries and lib32, if installed at all, contains the 32-bit ones.