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1 office 1 @node Enabling Relocatability
2 @section Enabling Relocatability
3  
4 It has been a pain for many users of GNU packages for a long time that
5 packages are not relocatable. It means a user cannot copy a program,
6 installed by another user on the same machine, to his home directory,
7 and have it work correctly (including i18n). So many users need to go
8 through @code{configure; make; make install} with all its
9 dependencies, options, and hurdles.
10  
11 Red Hat, Debian, and similar package systems solve the ``ease of
12 installation'' problem, but they hardwire path names, usually to
13 @file{/usr} or @file{/usr/local}. This means that users need root
14 privileges to install a binary package, and prevents installing two
15 different versions of the same binary package.
16  
17 A relocatable program can be moved or copied to a different location
18 on the file system. It is possible to make symlinks to the installed
19 and moved programs, and invoke them through the symlink. It is
20 possible to do the same thing with a hard link @emph{only} if the hard
21 link file is in the same directory as the real program.
22  
23 To configure a program to be relocatable, add
24 @option{--enable-relocatable} to the @command{configure} command line.
25  
26 On some OSes the executables remember the location of shared libraries
27 and prefer them over any other search path. Therefore, such an
28 executable will look for its shared libraries first in the original
29 installation directory and only then in the current installation
30 directory. Thus, for reliability, it is best to also give a
31 @option{--prefix} option pointing to a directory that does not exist
32 now and which never will be created, e.g.@:
33 @option{--prefix=/nonexistent}. You may use
34 @code{DESTDIR=@var{dest-dir}} on the @command{make} command line to
35 avoid installing into that directory.
36  
37 We do not recommend using a prefix writable by unprivileged users
38 (e.g.@: @file{/tmp/inst$$}) because such a directory can be recreated
39 by an unprivileged user after the original directory has been removed.
40 We also do not recommend prefixes that might be behind an automounter
41 (e.g.@: @file{$HOME/inst$$}) because of the performance impact of
42 directory searching.
43  
44 Here's a sample installation run that takes into account all these
45 recommendations:
46  
47 @example
48 ./configure --enable-relocatable --prefix=/nonexistent
49 make
50 make install DESTDIR=/tmp/inst$$
51 @end example
52  
53 Installation with @option{--enable-relocatable} will not work for
54 setuid or setgid executables, because such executables search only
55 system library paths for security reasons. Also, installation with
56 @option{--enable-relocatable} might not work on OpenBSD, when the
57 package contains shared libraries and libtool versions 1.5.xx are used.
58  
59 The runtime penalty and size penalty are negligible on GNU/Linux (just
60 one system call more when an executable is launched), and small on
61 other systems (the wrapper program just sets an environment variable
62 and executes the real program).