Understanding and Maintaining system indices

The two main parts of GoboLinux are /Programs and /System. If you stick to using InstallPackage and Compile, these two parts will be implicitly kept in sync by SymlinkProgram. But a lot of power lies in the fact that you can tune how these two worlds interact.

Program entries under /Programs feature a Current symlink pointing to a specific version that is “active” in the system. This Current version is taken as the default version when you don’t specify a version in scripts, and the link is updated when you install a new version with InstallPackage or Compile.

That doesn’t mean that you can only have one version linked into the system: you can have files of multiple versions show up in /Programs. In fact, when you install a new version with InstallPackage but keep the old version in /Programs, files for which there’s no version with the same name in the new package are still linked – this is especially useful for libraries.

For example, say program Foo 1.0 looks like this:

/Programs/Foo/1.0/lib/libfoo.so -> libfoo.so.1

Now, say, you install a new version, 2.0, which looks like this:

/Programs/Foo/2.0/lib/libfoo.so -> libfoo.so.2

The default behavior of SymlinkProgram is to replace symlinks under /Programs that belong to a different version of the same program. So, now, we’ll have the following links related to Foo under system:

/System/Index/bin/foo -> /Programs/Foo/2.0/bin/foo
/System/Index/include/foo.h -> /Programs/Foo/2.0/include/foo.h
/System/Index/lib/libfoo.so.2 -> /Programs/Foo/2.0/lib/libfoo.so.2
/System/Index/lib/libfoo.so -> /Programs/Foo/2.0/lib/libfoo.so.2
/System/Index/lib/libfoo.so.1 -> /Programs/Foo/1.0/lib/libfoo.so.1

So, now, when you run foo, it will fetch version 2.0 of the program through your system $PATH (which looks at /System/Index/bin). But, as you can see, libfoo.so.1 is still there. This way, if you have other programs installed in the system that are linked specifically to version 1 of the libfoo library will continue working.

This means you won’t have the old problem “I upgraded package Foo and now my other apps are broken”. Of course, you can still break things when you remove a version which other programs depend in (or if buggy programs link to a version independent name of a library (libfoo.so) but depend on features of a specific version).

Besides SymlinkProgram (see section “Compiling manually” and its reference entry for details on it), there are other scripts that give you more control over what is linked in the system and what is not.

With DisableProgram, you can remove from /System all links that refer to a specific version of a program, effectively “turning it off” – it is as if it were not present in the system.

With RemoveProgram, you can remove a program from /Programs and its references from /System in a single step.

See Removing programs for more details.