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### Variables for Installation Directories

Installation directories should always be named by variables, so it is easy to install in a nonstandard place. The standard names for these variables are described below. They are based on a standard filesystem layout; variants of it are used in SVR4, 4.4BSD, GNU/Linux, Ultrix v4, and other modern operating systems.

These two variables set the root for the installation. All the other installation directories should be subdirectories of one of these two, and nothing should be directly installed into these two directories.

`prefix`
  A prefix used in constructing the default values of the variables listed below. The default value of `prefix` should be `/usr/local`. When building the complete GNU system, the prefix will be empty and `/usr` will be a symbolic link to `/`. (If you are using Autoconf, write it as `@prefix@`.)

  Running `make install` with a different value of `prefix` from the one used to build the program should not recompile the program.

`exec_prefix`
  A prefix used in constructing the default values of some of the variables listed below. The default value of `exec_prefix` should be `$(prefix)`. (If you are using Autoconf, write it as `@exec_prefix@`.)

  Generally, `$(exec_prefix)` is used for directories that contain machine-specific files (such as executables and subroutine libraries), while `$(prefix)` is used directly for other directories.

  Running `make install` with a different value of `exec_prefix` from the one used to build the program should not recompile the program.

Executable programs are installed in one of the following directories.

`bindir`
  The directory for installing executable programs that users can run. This should normally be `/usr/local/bin`, but write it as `$(exec_prefix)/bin`. (If you are using Autoconf, write it as `@bindir@`.)
`sbindir`
  The directory for installing executable programs that can be run from the shell, but are only generally useful to system administrators. This should normally be `/usr/local/sbin`, but write it as `$(exec_prefix)/sbin`. (If you are using Autoconf, write it as `@sbindir@`.)
`libexecdir`
  The directory for installing executable programs to be run by other programs rather than by users. This directory should normally be `/usr/local/libexec`, but write it as `$(exec_prefix)/libexec`. (If you are using Autoconf, write it as `@libexecdir@`.)

Data files used by the program during its execution are divided into categories in two ways.

- Some files are normally modified by programs; others are never normally modified (though users may edit some of these).
- Some files are architecture-independent and can be shared by all machines at a site; some are architecture-dependent and can be shared only by machines of the same kind and operating system; others may never be shared between two machines.

This makes for six different possibilities. However, we want to discourage the use of architecture-dependent files, aside from object files and libraries. It is much cleaner to make other data files architecture-independent, and it is generally not hard.

Therefore, here are the variables Makefiles should use to specify directories:

`datadir`
  The directory for installing read-only architecture independent data files. This should normally be `/usr/local/share`, but write it as `$(prefix)/share`. (If you are using Autoconf, write it as `@datadir@`.) As a special exception, see `$(infodir)` and `$(includedir)` below.
`sysconfdir`
  The directory for installing read-only data files that pertain to a single machine-that is to say, files for configuring a host. Mailer and network configuration files, `/etc/passwd`, and so forth belong here. All the files in this directory should be ordinary ASCII text files. This directory should normally be `/usr/local/etc`, but write it as `$(prefix)/etc`. (If you are using Autoconf, write it as `@sysconfdir@`.)

  Do not install executables here in this directory (they probably belong in `$(libexecdir)` or `$(sbindir)`). Also do not install files that are modified in the normal course of their use (programs whose purpose is to change the configuration of the system excluded). Those probably belong in `$(localstatedir)`.

`sharedstatedir`
  The directory for installing architecture-independent data files which the programs modify while they run. This should normally be `/usr/local/com`, but write it as `$(prefix)/com`. (If you are using Autoconf, write it as `@sharedstatedir@`.)
`localstatedir`
  The directory for installing data files which the programs modify while they run, and that pertain to one specific machine. Users should never need to modify files in this directory to configure the package's operation; put such configuration information in separate files that go in `$(datadir)` or `$(sysconfdir)`. `$(localstatedir)` should normally be `/usr/local/var`, but write it as `$(prefix)/var`. (If you are using Autoconf, write it as `@localstatedir@`.)
`libdir`
  The directory for object files and libraries of object code. Do not install executables here, they probably ought to go in `$(libexecdir)` instead. The value of `libdir` should normally be `/usr/local/lib`, but write it as `$(exec_prefix)/lib`. (If you are using Autoconf, write it as `@libdir@`.)
`infodir`
  The directory for installing the Info files for this package. By default, it should be `/usr/local/info`, but it should be written as `$(prefix)/info`. (If you are using Autoconf, write it as `@infodir@`.)
`lispdir`
  The directory for installing any Emacs Lisp files in this package. By default, it should be `/usr/local/share/emacs/site-lisp`, but it should be written as `$(prefix)/share/emacs/site-lisp`.

  If you are using Autoconf, write the default as `@lispdir@`. In order to make `@lispdir@` work, you need the following lines in your `configure.in` file:

                lispdir='${datadir}/emacs/site-lisp'
                AC_SUBST(lispdir)

`includedir`
  The directory for installing header files to be included by user programs with the C `#include` preprocessor directive. This should normally be `/usr/local/include`, but write it as `$(prefix)/include`. (If you are using Autoconf, write it as `@includedir@`.)

  Most compilers other than GCC do not look for header files in directory `/usr/local/include`. So installing the header files this way is only useful with GCC. Sometimes this is not a problem because some libraries are only really intended to work with GCC. But some libraries are intended to work with other compilers. They should install their header files in two places, one specified by `includedir` and one specified by `oldincludedir`.

`oldincludedir`
  The directory for installing `#include` header files for use with compilers other than GCC. This should normally be `/usr/include`. (If you are using Autoconf, you can write it as `@oldincludedir@`.)

  The Makefile commands should check whether the value of `oldincludedir` is empty. If it is, they should not try to use it; they should cancel the second installation of the header files.

  A package should not replace an existing header in this directory unless the header came from the same package. Thus, if your Foo package provides a header file `foo.h`, then it should install the header file in the `oldincludedir` directory if either (1) there is no `foo.h` there or (2) the `foo.h` that exists came from the Foo package.

  To tell whether `foo.h` came from the Foo package, put a magic string in the file--part of a comment--and `grep` for that string.

Unix-style man pages are installed in one of the following:

`mandir`
  The top-level directory for installing the man pages (if any) for this package. It will normally be `/usr/local/man`, but you should write it as `$(prefix)/man`. (If you are using Autoconf, write it as `@mandir@`.)
`man1dir`
  The directory for installing section 1 man pages. Write it as `$(mandir)/man1`.
`man2dir`
  The directory for installing section 2 man pages. Write it as `$(mandir)/man2`
`...`
  Don't make the primary documentation for any GNU software be a man page. Write a manual in Texinfo instead. Man pages are just for the sake of people running GNU software on Unix, which is a secondary application only.
`manext`
  The file name extension for the installed man page. This should contain a period followed by the appropriate digit; it should normally be `.1`.
`man1ext`
  The file name extension for installed section 1 man pages.
`man2ext`
  The file name extension for installed section 2 man pages.
`...`
  Use these names instead of `manext` if the package needs to install man pages in more than one section of the manual.

And finally, you should set the following variable:

`srcdir`
  The directory for the sources being compiled. The value of this variable is normally inserted by the `configure` shell script. (If you are using Autconf, use `srcdir = @srcdir@`.)

For example:

         # Common prefix for installation directories.
         # NOTE: This directory must exist when you start the install.
         prefix = /usr/local
         exec_prefix = $(prefix)
         # Where to put the executable for the command `gcc'.
         bindir = $(exec_prefix)/bin
         # Where to put the directories used by the compiler.
         libexecdir = $(exec_prefix)/libexec
         # Where to put the Info files.
         infodir = $(prefix)/info

If your program installs a large number of files into one of the standard user-specified directories, it might be useful to group them into a subdirectory particular to that program. If you do this, you should write the `install` rule to create these subdirectories.

Do not expect the user to include the subdirectory name in the value of any of the variables listed above. The idea of having a uniform set of variable names for installation directories is to enable the user to specify the exact same values for several different GNU packages. In order for this to be useful, all the packages must be designed so that they will work sensibly when the user does so.