Jump to Emacs as shell

Emacs standing alone on a Linux Kernel

The purpose of this experiment is to see how emacs can work alone over a linux kernel.

The only external tool needed is mount .

This "root_fs_emacs" could be used as a normal partition or on live CD, but for this experiment, we'll run it with User Mode Linux.

1- Initialize a root_fs with at least 150 MB

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

2- Compile an emacs without X and statically

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

3- Install emacs as /sbin/init

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

4- Compile mount statically

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/

5- Boot linux

cd ~/uml umount /emacs linux ubd0=root_fs_emacs

Now, you can launch an emacs shell with

M-x eshell RET ls -l RET

and get:

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---------------------

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.

Another, more realistic, alternative would be to use a Common-Lisp implementation with a FFI and portable Hemlock.

Emacs as shell

Emacs can easily be used as shell:

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!