Question

Most packages using Autotools are user-level utilities or at least high-enough level to be completely under /usr, or low enough to be entirely below /usr.

I’m writing a package that would need to install some files into /bin, some into /sbin, /usr/bin and /usr/sbin. It’s replacing several existing binaries that are traditionally placed under those locations.

It also needs to install a PAM module in /lib/security (and obviously /usr/lib/security wouldn’t work).

Now the problem is: default configure’s prefix seems to be /usr/local. I can control that default in my configure.ac. And at least Gentoo Linux’s default is --prefix=/usr. That’s a problem because it overrides any defaults I put in my configure.ac.

I took a brief look at how other, similar packages are dealing with this issue. Here are my findings:

• bash-4.1 seems to install into /usr/bin, and distro build scripts move the bash binary to /bin
• Linux-PAM has hacks in configure.ac so that if prefix is /usr, it’s going to use /sbin and /lib for some of its files. It also sets the default prefix to /usr. I’m not sure what happens if the user passes a different --prefix.
• shadow-utils set exec_prefix to "" if prefix is /usr. Then bin_PROGRAMS refers to /bin, and ubindir is declared to point to ${prefix}/bin so that ubin_PROGRAMS refers to /usr/bin.

My questions are:

• What are other distros’ defaults for --prefix? Can I reasonably assume it’s always /usr? I’m only concerned about Linux at this point, not BSDs.
• Which of the above solutions seems the cleanest? Do you see some better solutions?
• What are potential problems with the above solutions? Are there some solutions to those problems?
• I’m fine with installing everything into /bin and creating compatibility symlinks. Does it make the problem simpler?
• Is there some other common build system that is acceptable for low-level system utilities that would better handle my requirements?

Feel free to ask for clarification of what I’m trying to do. Note that if I want to retain compatibility with what I’m replacing, if it used to ship binaries A and B, one in /sbin and one in /usr/bin, I think I just have to put replacements in those places or at least have symlinks. PAM modules also have a fixed install location.

I’m obviously going to upvote any useful answer. I an “accepted answer” I’m mostly looking for advice “what should I do”, what’s the cleanest solution to the problem and if applicable a discussion of options and drawbacks, pros and cons.

Answer 1

Essentially, the distinction between the / and the /usr hierarchies is not and should not lie in the hands of the packages’ upstream maintainer (read: Is not your responsibility). Since / should only contain files necessary for booting and making /usr available, it is an administrative decision what goes to /. For installations from source, this decision is made by the installer, and for distributions, by the package maintainer.

For a rationale, suppose someone is trying to build a chroot environment. The distinction between /usr and / is meaningless in the environment, and will not be made. All prefixes are set to /foo/bar/chroot, and any configure script messing with $prefix is likely to induce strange behaviour. The same arguments goes for scripts like the Debian packaging helpers, which rely on the usual $prefix semantics to work.

The cleanest solution is therefore the bash-4.1 solution. You have basically two clean options: Split your package into boot-critical and non-boot-critical parts, or let your configure script offer an alternative prefix for the boot-critical parts, which is set by default to /, leaving $prefix as /usr.