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<p><a href="#shell">Jump to Emacs as shell</a>
<h1>Emacs standing alone on a Linux Kernel</h1>
<p>The purpose of this experiment is to see how emacs can work alone
over a linux kernel.
<p>The only external tool needed is <code>mount</code>.
<p>This "root_fs_emacs" could be used as a normal partition or on live CD,
but for this experiment, we'll run it with
<a href="http://user-mode-linux.sourceforge.net">User Mode Linux</a>.
<h2>1- Initialize a root_fs with at least 150 MB</h2>
<pre>
cd ~/uml
dd if=/dev/zero of=root_fs_emacs bs=1k count=200k
yes y|mke2fs root_fs_emacs
mkdir /emacs
mount -o loop root_fs_emacs /emacs
cd /emacs
ln -s . emacs # we create this link to simplify config --prefix of emacs
cp -a /dev dev # we boldly copy the whole /dev
mkdir etc sbin tmp # some other directories not installed by emacs
cat >etc/fstab <<EOF
/dev/ubd0 / ext2 defaults 0 1
EOF
</pre>
<h2>2- Compile an emacs without X and statically</h2>
<pre>
cd ~/src
tar jxvf emacs-21.3.tar.bz2
cd emacs-21.3
CFLAGS=-static LDFLAGS=-static ./configure --without-x --prefix=/emacs
make && make install
</pre>
<h2>3- Install emacs as /sbin/init</h2>
<pre>
cd /emacs
ln bin/emacs sbin/init
cat >.emacs <<EOF
(message "init starting")
(setq auto-save-interval 0)
(defun shutdown ()
(interactive)
(when (yes-or-no-p "Really shut down the system? ")
;; actually, kill-emacs signals emacs ie. init, which makes linux panic.
(kill-emacs)))
(global-set-key "\C-x\C-c" 'shutdown)
(global-set-key "^\" 'keyboard-quit) ;; strangely, C-g does not work.
(call-process "/bin/mount" nil "*log*" t "-n" "-o" "rw,remount" "/")
(if (file-exists-p "/etc/mtab") (delete-file "/etc/mtab"))
(call-process "/bin/mount" nil "*log*" t "-f" "/dev/ubd0" "/")
(message "init done")
EOF
</pre>
<h2>4- Compile mount statically</h2>
<pre>
cd ~/src
tar jxvf util-linux-2.12a.tar.bz2
cd util-linux-2.12a
CFLAGS=-static LDFLAGS=-static ./configure
make && install -m 755 mount/umount mount/mount /emacs/bin/
</pre>
<h2>5- Boot linux</h2>
<pre>
cd ~/uml
umount /emacs
linux ubd0=root_fs_emacs
</pre>
<p>Now, you can launch an emacs shell with <pre> M-x eshell RET
ls -l RET
</pre>
<p>and get: <pre>
File Edit Options Buffers Tools Help
Welcome to the Emacs shell
/ # ls -l
total 21
drwxr-xr-x 2 0 0 1024 Jul 26 08:42 bin
drwxr-xr-x 1 0 0 0 Jan 1 1970 dev
lrwxrwxrwx 1 0 0 1 Jul 26 08:11 emacs -> .
drwxr-xr-x 2 0 0 1024 Jul 26 09:20 etc
drwxr-xr-x 2 0 0 2048 Jul 26 08:11 info
drwxr-xr-x 3 0 0 1024 Jul 26 08:11 libexec
drwx------ 2 0 0 12288 Jul 26 08:10 lost+found
drwxr-xr-x 3 0 0 1024 Jul 26 08:10 man
drwxr-xr-x 2 0 0 1024 Jul 26 08:11 sbin
drwxr-xr-x 3 0 0 1024 Jul 26 08:10 share
drwxr-xr-x 2 0 0 1024 Jul 26 09:15 tmp
/ #
--1-:---F1 *eshell* (EShell)--L20--All---------------------
</pre>
<p>Of course, quite a number of syscalls are missing from emacs (not
available as elisp primitives), so as it is, it would be hard enough to
do EVERYTHING with emacs, but this is a starting point.
<p>Another, more realistic, alternative would be to use a Common-Lisp
implementation with a FFI and portable Hemlock.
<h1><a name="shell"></a>Emacs as shell</h1>
<p>Emacs can easily be used as shell:
<pre>
echo /usr/bin/emacs >> /etc/shells
chsh -s /usr/bin/emacs GOODUSER
echo '(setenv "SHELL" "/bin/bash")' >> ~GOODUSER/.emacs
# in case the user wants to use M-x shell
# [ I use rather: (setenv "SHELL" "/usr/bin/clisp") ]
echo '(eshell)' >> ~GOODUSER/.emacs
# to launch eshell automatically.
# One could use: (dired default-directory) instead...
su - GOODUSER
# Hosanna!
</pre>
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