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Emacs standing alone on a Linux Kernel

 1 year ago
source link: http://informatimago.free.fr/i/linux/emacs-on-user-mode-linux.html
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Emacs standing alone on a Linux Kernel

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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!

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