Following the advice from some people here (thanks in particular to Thierry Laronde) I have got initrd and NFS root working so that I can use the same kernel binary for hard drives, RAID, and NFS root without making the kernel excessively large. I have written a document on what I have done because there seems no other good documentation on some of these things. It is attached. Any suggestions on improving the document (or how I could have done things differently to save myself some effort) will be appreciated. -- http://www.coker.com.au/bonnie++/ Bonnie++ hard drive benchmark http://www.coker.com.au/postal/ Postal SMTP/POP benchmark http://www.coker.com.au/projects.html Projects I am working on http://www.coker.com.au/~russell/ My home pageTitle: NFS Root With INITRD, GRUB, and Devfs
Once GRUB is compiled you have to install it to a floppy. There is a script
that just writes the stage1 and stage2 files to the raw floppy
device, AFAIK it is not possible to use a menu.lst file with this so it won't
work for anything other than a recovery disk where you type every command
entirely.
So I created a minix format floppy disk and installed GRUB to it, and
then put the following in boot/grub/menu.lst:
# give me 10 seconds to interrupt the boot and change things timeout 10 # boot from the first image by default default 0 # set the title that is displayed in the menu title net # I am not using dhcp/bootp so we have an ifconfig command to set our IP address # to 10.0.0.1 and the tftp server is 10.0.0.2 # use the dhcp, bootp, or rarp directives instead for a dynamic IP ifconfig --address=10.0.0.1 --server=10.0.0.2 # the root file system is a network disk root (nd) # specify the kernel file to load (/vmlinuz), --no-mem-option means not to # pass mem= to the kernel (I trust the kernel to find it's own memory) # load the root file system from /dev/ram (the initrd) and make /linuxrc the # init program. kernel --no-mem-option /vmlinuz root=/dev/ram init=/linuxrc # load the initrd from /boot/initrd on the tftp server initrd /boot/initrd # now boot the sucker! boot # now we've got an option to boot from the old version. title net-old ifconfig --address=10.0.0.1 --server=10.0.0.2 root (nd) kernel --no-mem-option /vmlinuz.old root=/dev/ram init=/linuxrc initrd /boot/initrd.old boot
This is the script I put in /etc/mkinitrd/scripts/nfs to set the initrd options for NFS. In Debian there are scripts to automatically create an initrd in the initrd-tools package. As part of this creation process the scripts in /etc/mkinitrd/scripts are all run, and the variable $INITRDDIR specifies the temporary directory that contains the new file system image.
#!/bin/sh # make a directory for mounting the NFS root file system mkdir $INITRDDIR/new-root # Create this script to be run on the initrd after modules have been loaded SCRIPT=$INITRDDIR/scripts/nfs.sh cat > $SCRIPT << END #!/bin/sh ifconfig eth0 10.0.0.1 mount -n 10.0.0.2:/var/tftpboot /new-root -orsize=8192,wsize=8192,lock,ro,port=2049,mountport=32790 mount -n none -t devfs /new-root/dev cd /new-root pivot_root . initrd umount /initrd/dev END chmod 755 $SCRIPT # my script needs ifconfig, pivot_root, and mount which aren't installed by # default, change ifconfig to dhclient, pump, etc for dynamic IP addresses cp /sbin/ifconfig /sbin/pivot_root $INITRDDIR/sbin cp /bin/mount $INITRDDIR/bin # tell /linuxrc to run init because the kernel won't do it, have to use exec # so that init gets PID=1 echo "exec init" >> $INITRDDIR/linuxrc
#!/bin/sh # assign a static IP address to the interface, replace it with a call to # dhclient, pump, etc for dynamic IP addresses ifconfig eth0 10.0.0.1 # mount the new root file system, specify the rsize and wsize options for # performance, specify the port numbers for NFS3 so that we don't need portmap # running mount -n 10.0.0.2:/var/tftpboot /new-root -orsize=8192,wsize=8192,lock,ro,port=2049,mountport=32790 # mount devfs under the new root. If the kernel was doing the pivot it would # manage this, but it's not so we have to do it. mount -n none -t devfs /new-root/dev # change to the new root (remove one reference to the old root) cd /new-root # make the current directory the new root, and remount the old root directory # under /initrd on the new root pivot_root . initrd # I'd like to do this but actually it'll fail. :( umount /initrd/dev
Debian has a file named /etc/mkinitrd/mkinitrd.conf to configure the process of making an initrd, for all my initrd systems I use the directive MODULES=none as I specify exactly the modules I need. Also for NFS we need ROOT= (IE we set it to an empty string). This means that the scripts to create the initrd don't try and figure out where the root file system is to load modules etc. This is necessary because we aren't following the regular initrd proceedure, and because I usually run the creation script on the NFS server machine (not on the diskless workstation).
Debian has the file /etc/mkinitrd/modules to specify which modules are to be loaded via modprobe during the start of the initrd process, I use nfs and tulip to load the network driver and the NFS client code. I also load usbcore, usb-uhci, input, keybdev, usbkbd, and hid so that I can use my USB keyboard before the real root file system is mounted.
I use the following in /etc/mkinitrd/scripts/devfs to remove un-needed (for devfs) entries in /dev:
#!/bin/sh rm -rf $INITRDDIR/dev/*
I use the following in /etc/mkinitrd/scripts/copy-needed-modules to parse the modules.dep file and install all modules that are needed by the modules I have specified into the lib/modules directory in the initrd:
#!/usr/bin/perl
open(DEP, "$ENV{MODULEDIR}/modules.dep") or die "Can't open modules.dep";
$/ = "\n\n";
# map of name to full path
my %names;
# map of path to dependencies
my %deps;
while(<DEP>)
{
$_ =~ s/\\\n/ /;
chomp;
my @line = split(':', $_);
my $name = $line[0];
$name =~ s/^.*\///;
$name =~ s/\..*$//;
$names{$name} = $line[0];
$deps{$line[0]} = $line[1];
}
close(DEP);
$/ = "\n";
open(MODULES, "grep -v ^# /etc/mkinitrd/modules | grep .|") or die "Can't open modules";
while(<MODULES>)
{
chomp;
foreach my $n ($names{$_}, split('\t', $deps{$names{$_}}) )
{
if(length($n) > 0)
{
$n =~ s/[ \t]*//g;
my $dir = $n;
$dir =~ s/[a-z0-9\-\.]*$//;
system("mkdir -p $ENV{INITRDDIR}$dir");
system("cp $n $ENV{INITRDDIR}$n");
}
}
}
To run the TFTP server I used the tftpd-hpa server. This is because it supports PXE network boots (which I plan to use at some future time). For what I am doing so far any TFTP server should work. Here is the configuration file for RLINETD (my favourite inetd), any inetd should work just as well:
service "tftp" {
protocol udp;
port "tftp";
user "root";
exec "/usr/sbin/in.tftpd -s /var/tftpboot";
nice 5;
instances 1;
}
The -s /var/tftpboot says that I want the /var/tftpboot to be
the root of the TFTP server.Then I put the following in /etc/exports:
/var/tftpboot 10.0.0.0/255.255.0.0(rw,no_root_squash)After running exportfs -r to export that everything was working.