hn-classics/_stories/2004/12854336.md

---
created_at: '2016-11-02T13:17:42.000Z'
title: Emacs standing alone on a Linux Kernel (2004)
url: http://www.informatimago.com/linux/emacs-on-user-mode-linux.html
author: Ivoah
points: 178
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comment_text: 
num_comments: 62
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created_at_i: 1478092662
_tags:
- story
- author_Ivoah
- story_12854336
objectID: '12854336'
year: 2004

---
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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][7]. 

## 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-xC-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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