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There's a series of libs available in the Ubuntu repositories like lib32stdc++6 and lib32ncurses5. You can either install these on a 64 bit system, or go for installing libstdc++6:i386 and libncurses5:i386. I'm interested to learn what the difference is between the two types of packages.

What is the actual difference? Why are they both available? Being under the impression that libx:i386 is the new way of doing things, is this method always preferred over installing the lib32x variant? Having a couple of lib32x and a couple of libx:i386 libraries already installed also makes me wonder if it would be a good idea to switch to only one type of package by replacing them with there counterparts.

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Good question. Looks like duplicate packages in the repositories. The only reason I can find for having this is efficient support for both multi-arch enabled systems and requirements for some single-arch enabled systems. However, I think all Ubuntu versions are multi-arch now. By the way, for reference three package links: libstdc++6, lib64stdc++6, lib32stdc++6 –  gertvdijk Jul 14 '13 at 13:53

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The practical difference between these packages is where the libraries are located. With libfoo:i386, libraries end up in multiarch paths such as /usr/lib/i386-linux-gnu whereas with lib32foo:amd64 libraries end up in the "old" paths such as /usr/lib32. In a distant future we would get rid of any lib32foo packages, but we are not there yet. At least lib32stdc++6 is needed for building gcc-X.Y at the moment, because it builds gcc-X.Y-multilib which is capable of supporting switches such as -m32 to select the target architecture (i.e. the architecture of the resulting binary). Without the lib32foo packages, the build-dependencies of gcc-X.Y would cross architecture boundaries and this is not yet supported. There are a few more issues that require keeping the lib32foo packages for a while.

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If gcc-X.Y-multilib is an exception requiring a lib32foo package, what about 'general' 32bit applications? Do they care if a library is located in either /usr/lib/i386-linux-gnu or /usr/lib32? –  Forage Jul 21 '13 at 16:41
    
Both paths are tried for libraries by binaries. To verify that look at /etc/ld.so.conf (and the corresponding directory). Multiarch paths take precedence over "old" paths, since the files are considered lexicographically. –  Helmut Grohne Jul 21 '13 at 16:43

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