This system is based on RedHat version 5.2 as the .rpm files are readily available on ftp.netwinder.org. I'm sure that other distributions will work just as well but I am more familiar with RedHat. I've found that I've learnt a bit about how Linux works by doing this and I hope other people can derive something useful out of it.
Thanks to Mike Montour for his NFS Rescue Package for lots of tips on getting started and having a working system to play with.
| std | Creates "standard" devices including core, full, mem, null, port, ram, tty, and zero |
| pty | Creates master and slave pty devices |
| console | Creates virtual console devices |
| fd | Symbolic links for fd and stdio devices (not to be confused with floppy disk device files) |
Other devices which may be of use, but not in my particular application are as follows.
| ttyS0, ttyS1 | Serial port devices |
| hda | First IDE hard disk device files |
| audio | Sound driver devices |
Note that due to the way MAKEDEV calculates the major numbers
for devices, the kernel running the script needs to have those options
compiled in to it. For example, you can't create the device files for
the loopback or audio devices without having loopback or audio support
compiled in to the currently running kernel, respectively.
A Bourne shell
Extract a version of your favourite shell into the /bin
directory. If you're feeling lucky (punk) then extract a dynamically
linked version. If you just want to muck around before getting the
dynamic linker working then use a statically linked version. I
recommend /bin/ash.static from the ash rpm package.
Writing /sbin/init
Now, the very last thing the Linux kernel does is try and execute
/sbin/init which is the very first process run in user-land.
From init/main.c from the kernel source code:
/*
* We try each of these until one succeeds.
*
* The Bourne shell can be used instead of init if we are
* trying to recover a really broken machine.
*/
if (execute_command)
execve(execute_command,argv_init,envp_init);
execve("/sbin/init",argv_init,envp_init);
execve("/etc/init",argv_init,envp_init);
execve("/bin/init",argv_init,envp_init);
execve("/bin/sh",argv_init,envp_init);
panic("No init found. Try passing init= option to kernel.");
Normally the version of init installed on a Linux system, in
the case of the RedHat distribution, is the SysVinit
package. This is a fairly complicated series of shell scripts in
/etc/init.d involving runlevels and such. For a minimal
Linux system I consider this overkill and the whole arrangement can
consist of a simple shell script.An simple example of an init script is below.
#!/bin/ash echo Welcome to nano-linux /bin/ashThis will present you with a (single) console shell logged in as root. Note that if you log out of it your system basically hangs. I think the kernel is still runing and scheduling processes but you may have no way of logging in. What is needed is to run ash as a login shell. According to the manual page for ash,
If the first character of argument zero to the shell is
``-'', the shell is assumed to be a login shell, and the
files /etc/profile and .profile are read if they exist.
I'm not sure how you do this from a shell script. A C program may be
able to do this by fiddling with the arguments to execv().
# ln -s /lib/ld-2.0.*.so /lib/ld-linux.so.2
# ln -s /lib/libc-2.0.*.so /lib/libc.so.6
# ln -s /lib/ld-linux.so.2 /usr/lib/ld.so.1
The glibc RPM also contains the math library, /libm
and many others which may be needed by other applications.
echo >/etc/mtab
mount /proc /proc -t proc
To get some more useful network things happening, the following binaries may be needed. This information can probably be retrieved or set from the /proc directory.