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[emacs.git] / INSTALL

GNU Emacs Installation Guide
Copyright (c) 1992, 1994, 1996, 1997 Free software Foundation, Inc.

   Permission is granted to anyone to make or distribute verbatim copies
   of this document as received, in any medium, provided that the
   copyright notice and permission notice are preserved,
   and that the distributor grants the recipient permission
   for further redistribution as permitted by this notice.

   Permission is granted to distribute modified versions
   of this document, or of portions of it,
   under the above conditions, provided also that they
   carry prominent notices stating who last changed them,
   and that any new or changed statements about the activities
   of the Free Software Foundation are approved by the Foundation.


ADDITIONAL DISTRIBUTION FILES

* leim-M.N.tar.gz

The Emacs Lisp code for input methods for various international
character scripts is distributed in a separate tar file because of its
large size.  This file is called leim-M.N.tar.gz, with the same
version number as Emacs, and it unpacks into the directory
emacs-M.N/leim.  Thus, if you unpack it in the same directory where
you unpacked the Emacs distribution, it fills in a subdirectory
of the Emacs distribution.

If you have already unpacked the Leim tar file into a subdirectory of
the Emacs sources, building and installing Emacs automatically
installs the input method support as well.  If you unpack the Leim tar
file into the Emacs sources after building and installing Emacs, just
build Emacs again and install it again.

* intlfonts-VERSION.tar.gz

The intlfonts distribution contains X11 fonts that Emacs needs in
order to display international characters.  If you see a non-ASCII
character appear as a hollow box, that means you don't have a font for
it.  You might find a font in the intlfonts distribution.  If some
characters don't look right, or appear improperly aligned, a font
from the intlfonts distribution might look better.

The intlfonts distribution contains its own installation instructions,
in the intlfonts/README file.


BUILDING AND INSTALLATION:

(This is for a Unix or Unix-like system.  For MSDOS, see below; search
for MSDOG.  For Windows NT or Windows 95, see the file nt/INSTALL.)

1) Make sure your system has enough swapping space allocated to handle
a program whose pure code is 900k bytes and whose data area is at
least 400k and can reach 8Mb or more.  If the swapping space is
insufficient, you will get an error in the command `temacs -batch -l
loadup dump', found in `./src/Makefile.in', or possibly when
running the final dumped Emacs.
 
Building Emacs requires about 70 Mb of disk space (including the Emacs
sources).  Once installed, Emacs occupies about 35 Mb in the file
system where it is installed; this includes the executable files, Lisp
libraries, miscellaneous data files, and on-line documentation.  If
the building and installation take place in different directories,
then the installation procedure momentarily requires 70+35 Mb.

2) Consult `./etc/MACHINES' to see what configuration name you should
give to the `configure' program.  That file offers hints for
getting around some possible installation problems.

3) You can build Emacs in the top-level Emacs source directory
or in a separate directory.

3a) To build in the top-level Emacs source directory, go to that
directory and run the program `configure' as follows:

    ./configure [CONFIGURATION-NAME] [--OPTION[=VALUE]] ...

The CONFIGURATION-NAME argument should be a configuration name given
in `./etc/MACHINES', with the system version number added at the end.

You should try first omitting CONFIGURATION-NAME.  This way,
`configure' will try to guess your system type.  If it cannot guess,
or if something goes wrong in building or installing Emacs this way,
try again specifying the proper CONFIGURATION-NAME explicitly.

If you don't want X support, specify `--with-x=no'.  If you omit this
option, `configure' will try to figure out for itself whether your
system has X, and arrange to use it if present.

The `--x-includes=DIR' and `--x-libraries=DIR' options tell the build
process where the compiler should look for the include files and
object libraries used with the X Window System.  Normally, `configure'
is able to find them; these options are necessary if you have your X
Window System files installed in unusual places.  These options also
accept a list of directories, separated with colons.

To get more attractive menus, you can specify an X toolkit when you
configure Emacs; use the option `--with-x-toolkit=TOOLKIT', where
TOOLKIT is `athena' or `motif' (`yes' and `lucid' are synonyms for
`athena').  On some systems, it does not work to use a toolkit with
shared libraries.

The `--with-gcc' option specifies that the build process should
compile Emacs using GCC.  If you don't want to use GCC, specify
`--with-gcc=no'.  If you omit this option, `configure' will search
for GCC in your path, and use it if present.

If you want the Emacs mail reader RMAIL to read mail from a POP
server, you must specify `--with-pop'.  This provides support for the
POP3 protocol; older versions are not supported.  For
Kerberos-authenticated POP add `--with-kerberos', for Hesiod support
add `--with-hesiod'.  These options enable Emacs to use POP; whether
Emacs uses POP is controlled by individual users--see the Rmail
chapter of the Emacs manual.

The `--prefix=PREFIXDIR' option specifies where the installation process
should put emacs and its data files.  This defaults to `/usr/local'.
- Emacs (and the other utilities users run) go in PREFIXDIR/bin
  (unless the `--exec-prefix' option says otherwise).
- The architecture-independent files go in PREFIXDIR/share/emacs/VERSION
  (where VERSION is the version number of Emacs, like `19.27').
- The architecture-dependent files go in
  PREFIXDIR/libexec/emacs/VERSION/CONFIGURATION
  (where CONFIGURATION is the configuration name, like mips-dec-ultrix4.2),
  unless the `--exec-prefix' option says otherwise.

The `--exec-prefix=EXECDIR' option allows you to specify a separate
portion of the directory tree for installing architecture-specific
files, like executables and utility programs.  If specified,
- Emacs (and the other utilities users run) go in EXECDIR/bin, and
- The architecture-dependent files go in
  EXECDIR/libexec/emacs/VERSION/CONFIGURATION.
EXECDIR/bin should be a directory that is normally in users' PATHs.

For example, the command

    ./configure mips-dec-ultrix --with-x11

configures Emacs to build for a DECstation running Ultrix, with
support for the X11 window system.

`configure' doesn't do any compilation or installation
itself.  It just creates the files that influence those things:
`./Makefile', `lib-src/Makefile', `oldXMenu/Makefile',
`lwlib/Makefile', `src/Makefile', and `./src/config.h'.  For details
on exactly what it does, see the section called `CONFIGURATION BY
HAND', below.

When it is done, `configure' prints a description of what it did and
creates a shell script `config.status' which, when run, recreates the
same configuration.  If `configure' exits with an error after
disturbing the status quo, it removes `config.status'.  `configure'
also creates a file `config.cache' that saves the results of its tests
to make reconfiguring faster, and a file `config.log' containing compiler
output (useful mainly for debugging `configure').  You can give
`configure' the option `--cache-file=FILE' to use the results of the
tests in FILE instead of `config.cache'.  Set FILE to `/dev/null' to
disable caching, for debugging `configure'.

The work of `configure' can be done by editing various files in the
distribution, but using `configure' is easier.  See the section called
"CONFIGURATION BY HAND" below if you want to do the configuration
yourself.

3b) To build in a separate directory, go to that directory
and run the program `configure' as follows:

    SOURCE-DIR/configure CONFIGURATION-NAME [--OPTION[=VALUE]] ...

SOURCE-DIR refers to the top-level Emacs source directory which is
where Emacs's configure script is located.  `configure' looks for the
Emacs source code in the directory that `configure' is in.

To build in a separate directory, you must use a version of `make'
that supports the `VPATH' variable, such as GNU `make'.

3c) Some people try to build in a separate directory by filling
it full of symlinks to the files in the real source directory.
If you do that, `make all' does work, but `make install' fails:
it copies the symbolic links rather than the actual files.

As far as is known, there is no particular reason to use
a directory full of links rather than use the standard GNU
facilities to build in a separate directory (see 3b above).

4) Look at `./lisp/paths.el'; if some of those values are not right
for your system, set up the file `./lisp/site-init.el' with Emacs
Lisp code to override them; it is not a good idea to edit paths.el
itself.  YOU MUST USE THE LISP FUNCTION `setq' TO ASSIGN VALUES,
rather than `defvar', as used by `./lisp/paths.el'.  For example,

     (setq news-inews-program "/usr/bin/inews")

is how you would override the default value of the variable
news-inews-program (which is "/usr/local/inews").

Before you override a variable this way, *look at the value* that the
variable gets by default!  Make sure you know what kind of value the
variable should have.  If you don't pay attention to what you are
doing, you'll make a mistake.

5) Put into `./lisp/site-init.el' or `./lisp/site-load.el' any Emacs
Lisp code you want Emacs to load before it is dumped out.  Use
site-load.el for additional libraries if you arrange for their
documentation strings to be in the etc/DOC file (see
src/Makefile.in if you wish to figure out how to do that).  For all
else, use site-init.el.

If you set load-path to a different value in site-init.el or
site-load.el, Emacs will use *precisely* that value when it starts up
again.  If you do this, you are on your own!

Note that, on some systems, the code you place in site-init.el must
not use expand-file-name or any other function which may look
something up in the system's password and user information database.
See `./etc/PROBLEMS' for more details on which systems this affects.

The `site-*.el' files are nonexistent in the distribution.  You do not
need to create them if you have nothing to put in them.

6) Refer to the file `./etc/TERMS' for information on fields you may
wish to add to various termcap entries.  The files `./etc/termcap.ucb'
and `./etc/termcap.dat' may already contain appropriately-modified
entries.

7) Run `make' in the top directory of the Emacs distribution to finish
building Emacs in the standard way.  The final executable file is
named `src/emacs'.  You can execute this file "in place" without
copying it, if you wish; then it automatically uses the sibling
directories ../lisp, ../lib-src, ../info.

Or you can "install" the executable and the other Emacs into their
installed locations, with `make install'.  By default, Emacs's files
are installed in the following directories:

`/usr/local/bin' holds the executable programs users normally run -
                `emacs', `etags', `ctags', `b2m', `emacsclient',
                and `rcs-checkin'.

`/usr/local/share/emacs/VERSION/lisp' holds the Emacs Lisp library;
                `VERSION' stands for the number of the Emacs version
                you are installing, like `18.59' or `19.27'.  Since the
                Lisp library changes from one version of Emacs to
                another, including the version number in the path
                allows you to have several versions of Emacs installed
                at the same time; in particular, you don't have to
                make Emacs unavailable while installing a new version.

`/usr/local/share/emacs/VERSION/site-lisp' holds the local Emacs Lisp
                files installed for Emacs version VERSION only.

`/usr/local/share/emacs/site-lisp' holds the local Emacs Lisp
                files installed for all Emacs versions.

                When Emacs is installed, it searches for its Lisp files
                in `/usr/local/share/emacs/VERSION/site-lisp', then in
                `/usr/local/share/emacs/site-lisp', and finally in
                `/usr/local/share/emacs/VERSION/lisp'.

`/usr/local/share/emacs/VERSION/etc' holds the Emacs tutorial, the DOC
                file, the `yow' database, and other
                architecture-independent files Emacs might need while
                running.  VERSION is as specified for `.../lisp'.

`/usr/local/com/emacs/lock' contains files indicating who is editing
                what, so Emacs can detect editing clashes between
                users.

`/usr/local/libexec/emacs/VERSION/CONFIGURATION-NAME' contains executable
                programs used by Emacs that users are not expected to
                run themselves.
                `VERSION' is the number of the Emacs version you are
                installing, and `CONFIGURATION-NAME' is the argument
                you gave to the `configure' program to identify the
                architecture and operating system of your machine,
                like `mips-dec-ultrix' or `sparc-sun-sunos'.  Since
                these files are specific to the version of Emacs,
                operating system, and architecture in use, including
                the configuration name in the path allows you to have
                several versions of Emacs for any mix of machines and
                operating systems installed at the same time; this is
                useful for sites at which different kinds of machines
                share the file system Emacs is installed on.

`/usr/local/info' holds the on-line documentation for Emacs, known as
                "info files".  Many other GNU programs are documented
                using info files as well, so this directory stands
                apart from the other, Emacs-specific directories.

`/usr/local/man/man1' holds the man pages for the programs installed
                in `/usr/local/bin'.

If these directories are not what you want, you can specify where to
install Emacs's libraries and data files or where Emacs should search
for its Lisp files by giving values for `make' variables as part of
the command.  See the section below called `MAKE VARIABLES' for more
information on this.

8) Check the file `dir' in your site's info directory (usually
/usr/local/info) to make sure that it has a menu entry for the Emacs
info files.

9) If your system uses lock files to interlock access to mailer inbox files,
then you might need to make the movemail program setuid or setgid
to enable it to write the lock files.  We believe this is safe.

10) You are done!  You can remove executables and object files from
the build directory by typing `make clean'.  To also remove the files
that `configure' created (so you can compile Emacs for a different
configuration), type `make distclean'.



MAKE VARIABLES

You can change where the build process installs Emacs and its data
files by specifying values for `make' variables as part of the `make'
command line.  For example, if you type

    make install bindir=/usr/local/gnubin

the `bindir=/usr/local/gnubin' argument indicates that the Emacs
executable files should go in `/usr/local/gnubin', not
`/usr/local/bin'.

Here is a complete list of the variables you may want to set.

`bindir' indicates where to put executable programs that users can
        run.  This defaults to /usr/local/bin.

`datadir' indicates where to put the architecture-independent
        read-only data files that Emacs refers to while it runs; it
        defaults to /usr/local/share.  We create the following
        subdirectories under `datadir':
        - `emacs/VERSION/lisp', containing the Emacs Lisp library, and
        - `emacs/VERSION/etc', containing the Emacs tutorial, the DOC
                file, and the `yow' database.
        `VERSION' is the number of the Emacs version you are installing,
        like `18.59' or `19.0'.  Since these files vary from one version
        of Emacs to another, including the version number in the path
        allows you to have several versions of Emacs installed at the
        same time; this means that you don't have to make Emacs
        unavailable while installing a new version.

`sharedstatedir' indicates where to put architecture-independent data files
        that Emacs modifies while it runs; it defaults to
        /usr/local/com.  We create the following
        subdirectories under `sharedstatedir':
        - `emacs/lock', containing files indicating who is editing
                what, so Emacs can detect editing clashes between
                users.

`libexecdir' indicates where to put architecture-specific data files that
        Emacs refers to as it runs; it defaults to `/usr/local/libexec'.
        We create the following subdirectories under `libexecdir':
        - `emacs/VERSION/CONFIGURATION-NAME', containing executable
                programs used by Emacs that users are not expected to run
                themselves.  
        `VERSION' is the number of the Emacs version you are installing,
        and `CONFIGURATION-NAME' is the argument you gave to the
        `configure' program to identify the architecture and operating
        system of your machine, like `mips-dec-ultrix' or
        `sparc-sun-sunos'.  Since these files are specific to the version
        of Emacs, operating system, and architecture in use, including
        the configuration name in the path allows you to have several
        versions of Emacs for any mix of machines and operating systems
        installed at the same time; this is useful for sites at which
        different kinds of machines share the file system Emacs is
        installed on.

`infodir' indicates where to put the info files distributed with
        Emacs; it defaults to `/usr/local/info'.

`mandir' indicates where to put the man pages for Emacs and its
        utilities (like `etags'); it defaults to
        `/usr/local/man/man1'.

`manext' gives the extension the man pages should be installed with.
        It should contain a period, followed by the appropriate
        digit.  It defaults to `.1'.  For example given the default
        values for `mandir' and `manext', the Emacs man page would be
        installed as `/usr/local/man/man1/emacs.1'.

`prefix' doesn't give a path for any specific part of Emacs; instead,
        its value is used to determine the defaults for all the
        architecture-independent path variables - `datadir',
        `sharedstatedir', `infodir', and `mandir'.  Its default value is
        `/usr/local'; the other variables add on `lib' or `man' to it
        by default.

        For example, suppose your site generally places GNU software
        under `/usr/users/software/gnusoft' instead of `/usr/local'.
        By including
            `prefix=/usr/users/software/gnusoft'
        in the arguments to `make', you can instruct the build process
        to place all of the Emacs data files in the appropriate
        directories under that path.

`exec_prefix' serves the same purpose as `prefix', but instead
        determines the default values for the architecture-dependent
        path variables - `bindir' and `libexecdir'.

The above variables serve analogous purposes in the makefiles for all
GNU software; this variable is specific to Emacs.

`archlibdir' indicates where Emacs installs and expects the executable
        files and other architecture-dependent data it uses while
        running.  Its default value, based on `libexecdir' (which
        see), is `/usr/local/libexec/emacs/VERSION/CONFIGURATION-NAME'
        (where VERSION and CONFIGURATION-NAME are as described above).

Remember that you must specify any variable values you need each time
you run `make' in the top directory.  If you run `make' once to build
emacs, test it, and then run `make' again to install the files, you
must provide the same variable settings each time.  To make the
settings persist, you can edit them into the `Makefile' in the top
directory, but be aware that running the `configure' program erases
`Makefile' and rebuilds it from `Makefile.in'.

The path for finding Lisp files is specified in src/paths.h,
a file which is generated by running configure.  To change the path,
you can edit the definition of PATH_LOADSEARCH in that file
before you run `make'.

The top-level Makefile stores the variable settings it used in the
Makefiles for the subdirectories, so you don't have to specify them
when running make in the subdirectories.


CONFIGURATION BY HAND

Instead of running the `configure' program, you have to perform the
following steps.

1) Copy `./src/config.in' to `./src/config.h'.

2) Consult `./etc/MACHINES' to see what configuration name you should
use for your system.  Look at the code of the `configure' script to
see which operating system and architecture description files from
`src/s' and `src/m' should be used for that configuration name.  Edit
`src/config.h', and change the two `#include' directives to include
the appropriate system and architecture description files.

2) Edit `./src/config.h' to set the right options for your system.  If
you need to override any of the definitions in the s/*.h and m/*.h
files for your system and machine, do so by editing config.h, not by
changing the s/*.h and m/*.h files.  Occasionally you may need to
redefine parameters used in `./lib-src/movemail.c'.

3) Create src/Makefile and lib-src/Makefile from the corresponding
`Makefile.in' files.  First copy `Makefile.in' to `Makefile.c',
then edit in appropriate substitutions for the @...@ constructs,
and then copy the shell commands near the end of `configure'
that run cpp to construct `Makefile'.

4) Create `Makefile' files in various other directories
from the corresponding `Makefile.in' files.  This isn't so hard,
just a matter of substitution.

The `configure' script is built from `configure.in' by the `autoconf'
program.  You need version 2.0 or newer of `autoconf' to rebuild `configure'.

BUILDING GNU EMACS BY HAND

Once Emacs is configured, running `make' in the top directory performs
the following steps.

1) Run `make src/paths.h' in the top directory.  This produces
`./src/paths.h' from the template file `./src/paths.in', changing
the paths to the values specified in `./Makefile'.

2) Go to directory `./lib-src' and run `make'.  This creates
executables named `ctags' and `etags' and `wakeup' and `make-docfile'
and `digest-doc' and `test-distrib'.  And others.

3) Go to directory `./src' and Run `make'.  This refers to files in
the `./lisp' and `./lib-src' subdirectories using names `../lisp' and
`../lib-src'.

This creates a file `./src/emacs' which is the runnable Emacs,
which has another name that contains a version number.
Each time you do this, that version number increments in the last place.

It also creates a file in `./etc' whose name is `DOC' followed by the
current Emacs version.  This file contains documentation strings for
all the functions in Emacs.  Each time you run make to make a new
emacs, a new DOC file with a new name is made.  You must keep the DOC
file for an Emacs version as long as you keep using that Emacs
version.


INSTALLATION BY HAND

The steps below are done by running `make install' in the main
directory of the Emacs distribution.

1) Copy `./lisp' and its subdirectories, `./etc', and the executables
in `./lib-src' to their final destinations, as selected in `./src/paths.h'.

Strictly speaking, not all of the executables in `./lib-src' need be copied.
- The programs `cvtmail', `emacsserver', `fakemail', `hexl',
    `movemail', `profile', `rcs2log', `timer', `vcdiff', `wakeup',
    and `yow' are used by Emacs; they do need to be copied.
- The programs `etags', `ctags', `emacsclient', `b2m', and `rcs-checkin'
    are intended to be run by users; they are handled below.
- The programs `make-docfile' and `test-distrib' were
    used in building Emacs, and are not needed any more.
- The programs `digest-doc' and `sorted-doc' convert a `DOC' file into
    a file for users to read.  There is no important reason to move them.

2) Copy the files in `./info' to the place specified in
`./lisp/site-init.el' or `./lisp/paths.el'.  Note that if the
destination directory already contains a file named `dir', you
probably don't want to replace it with the `dir' file in the Emacs
distribution.  Instead, you should make sure that the existing `dir'
file contains an appropriate menu entry for the Emacs info.

3) Create a directory for Emacs to use for clash detection, named as
indicated by the PATH_LOCK macro in `./src/paths.h'.

4) Copy `./src/emacs' to `/usr/local/bin', or to some other directory
in users' search paths.  `./src/emacs' has an alternate name
`./src/emacs-EMACSVERSION'; you may wish to make a symbolic link named
`/usr/local/bin/emacs' pointing to that alternate name, as an easy way
of installing different versions.

You can delete `./src/temacs'.

5) Copy the programs `b2m', `emacsclient', `ctags', `etags', and
`rcs-checkin' from `./lib-src' to `/usr/local/bin'.  These programs are
intended for users to run.

6) Copy the man pages in `./etc' for emacs, ctags, and etags into the
appropriate man directories.

7) The files in the `./src' subdirectory, except for `emacs', are not
used by Emacs once it is built.  However, it is very desirable to keep
the source on line for debugging.


PROBLEMS

See the file PROBLEMS in etc subdirectory for a list of various
problems sometimes encountered, and what to do about them.


Installation on MSDOG (a.k.a. MSDOS)

To install on MSDOG, you need to have the GNU C compiler for MSDOG
(also known as djgpp), GNU Make, rm, mv, and sed.  See the remarks in
config.bat for more information about locations and versions.  The
file etc/FAQ includes pointers to Internet sites where you can find
the necessary utilities; search for "MS-DOS".  The configuration step
(see below) will test for these utilities and will refuse to continue
if any of them isn't found.

If you are building the MSDOG version of Emacs on an MSDOG-like system
which supports long file names (e.g. Windows 95), you need to make
sure that long file names are handled consistently both when you
unpack the distribution and compile it.  If you intend to compile with
DJGPP v2.0 or later, and long file names support is enabled (LFN=y in
the environment), you need to unpack Emacs distribution in a way that
doesn't truncate the original long filenames to the DOS 8.3 namespace;
the easiest way to do this is to use djtar program which comes with
DJGPP, since it will note the LFN setting and behave accordingly.
DJGPP v1 doesn't support long filenames, so you must unpack Emacs with
a program that truncates the filenames to 8.3 naming as it extracts
files; again, using djtar after setting LFN=n is the recommended way.
You can build Emacs with LFN=n even if you use DJGPP v2, if some of
your tools don't support long file names: just ensure that LFN is set
to `n' during both unpacking and compiling.

(By the time you read this, you have already unpacked the Emacs
distribution, but if the explanations above imply that you should have
done it differently, it's safer to delete the directory tree created
by the unpacking program and unpack Emacs again, than to risk running
into problems during the build process.)

It is important to understand that the runtime support of long file
names by the Emacs binary is NOT affected by the LFN setting during
compilation; Emacs compiled with DJGPP v2.0 or later will always
support long file names on Windows 95 no matter what was the setting
of LFN at compile time.  However, if you compiled with LFN disabled
and want to enable LFN support after Emacs was already built, you need
to make sure that the support files in the lisp, etc and info
directories are called by their original long names as found in the
distribution.  You can do this either by renaming the files manually,
or by extracting them from the original distribution archive with
djtar after you set LFN=y in the environment.

To unpack Emacs with djtar, type this command:

    djtar -x emacs.tgz

(This assumes that the Emacs distribution is called `emacs.tgz' on
your system.)

When unpacking is done, a directory called `emacs-XX.YY' will be
created, where XX.YY is the Emacs version.  To build and install
Emacs, chdir to that directory and type these commands:

    config msdos
    make install

Building Emacs creates executable files in the src and lib-src
directories.  Installing Emacs on MSDOS moves these executables to a
sibling directory called bin.  For example, if you build in directory
/emacs, installing moves the executables from /emacs/src and
/emacs/lib-src to the directory /emacs/bin, so you can then delete the
subdirectories /emacs/src and /emacs/lib-src if you wish.  The only
subdirectories you need to keep are bin, lisp, etc and info.  The bin
subdirectory should be added to your PATH.  The msdos subdirectory
includes a PIF and an icon file for Emacs which you might find useful
if you run Emacs under MS Windows.

Emacs on MSDOS finds the lisp, etc and info directories by looking in
../lisp, ../etc and ../info, starting from the directory where the
Emacs executable was run from.  You can override this by setting the
environment variables EMACSDATA (for the location of `etc' directory),
EMACSLOADPATH (for the location of `lisp' directory) and INFOPATH (for
the location of the `info' directory).

MSDOG is a not a multitasking operating system, so Emacs features such
as asynchronous subprocesses that depend on multitasking will not
work.  Synchronous subprocesses do work.

Version 2.0 of djgpp has two bugs that affect Emacs.  We've included
corrected versions of two files from djgpp in the msdos subdirectory:
is_exec.c and sigaction.c.  To work around the bugs, compile these
files and link them into temacs.  Djgpp version 2.01 have these bugs
fixed, so upgrade if you can before building Emacs.