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1. Enabling Relocatability

It has been a pain for many users of GNU packages for a long time that packages are not relocatable. It means a user cannot copy a program, installed by another user on the same machine, to his home directory, and have it work correctly (including i18n). So many users need to go through configure; make; make install with all its dependencies, options, and hurdles.

Red Hat, Debian, and similar package systems solve the “ease of installation” problem, but they hardwire path names, usually to ‘/usr’ or ‘/usr/local’. This means that users need root privileges to install a binary package, and prevents installing two different versions of the same binary package.

A relocatable program can be moved or copied to a different location on the filesystem. It is possible to make symlinks to the installed and moved programs, and invoke them through the symlink. It is possible to do the same thing with a hard link only if the hard link file is in the same directory as the real program.

To configure a program to be relocatable, add ‘--enable-relocatable’ to the configure command line.

On some OSes the executables remember the location of shared libraries and prefer them over any other search path. Therefore, such an executable will look for its shared libraries first in the original installation directory and only then in the current installation directory. Thus, for reliability, it is best to also give a ‘--prefix’ option pointing to a directory that does not exist now and which never will be created, e.g. ‘--prefix=/nonexistent’. You may use DESTDIR=dest-dir on the make command line to avoid installing into that directory.

We do not recommend using a prefix writable by unprivileged users (e.g. ‘/tmp/inst$$’) because such a directory can be recreated by an unprivileged user after the original directory has been removed. We also do not recommend prefixes that might be behind an automounter (e.g. ‘$HOME/inst$$’) because of the performance impact of directory searching.

Here's a sample installation run that takes into account all these recommendations:

 
./configure --enable-relocatable --prefix=/nonexistent
make
make install DESTDIR=/tmp/inst$$

Installation with ‘--enable-relocatable’ will not work for setuid or setgid executables, because such executables search only system library paths for security reasons. Also, installation with ‘--enable-relocatable’ might not work on OpenBSD, when the package contains shared libraries and libtool versions 1.5.xx are used.

The runtime penalty and size penalty are negligible on GNU/Linux (just one system call more when an executable is launched), and small on other systems (the wrapper program just sets an environment variable and executes the real program).


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