Well, this how-to for the diskless Ubuntu setup is not usual. The main point is that all our infrastructure is based on CentOS, but sometimes (like in this case) we must support different Linux distributions for our clients. That is why all server-side configuration will be related to CentOS, and client-side to Ubuntu.
In difference to the official
DisklessHowto, this one allows you to prepare a shared installation which can be used by any number of clients simultaneously. All changes to the mounted root will resist in ramfs, so no changes will be written to the NFS, and everything will be gone after restart. This feature in some (many) cases is treated as an advantage.
However, it is recommended to read
DisklessHowto from the Ubuntu site, since all basics related to network boot for Ubuntu described there much better. Also, I took some parts from their documentations to my howto. I believe they
wouldn't mind.
Requirements
- DHCP server
- TFTP server
- NFS server
All my servers uses CentOS, so I will describe server-side the configuration only for this system.
Current server setup is based on CentOS 6.2 x86_64 with IP 192.168.1.10.
Step by step
I. DHCP
I will not describe basics of DHCP configuration, you can easily google it. In order to make PXE work, you need to put just these two option to your DHCP configuration:
filename pxelinux.0;
next-server 192.168.1.10;
Where next-server provides with an address of your TFTP server. It can be put in almost any section of dhcpd.conf: global, class, subnet, pool, group or host.
II. TFTP
1. Install tftp daemon and syslinux package. Syslinux is available from
rpmforge.
# yum install tftp-server syslinux
# chkconfig tftp on
# service tftp start
2. Copy pxelinux files to tftp directory:
# cp /usr/share/syslinux/pxelinux.0 /tftpboot/
# cp /usr/share/syslinux/vesamenu.c32 /tftpboot/
3. Configure pxelinux
# mkdir /tftpboot/pxelinux.cfg
# cat << EOF > /tftpboot/pxelinux.cfg/default
DEFAULT vesamenu.c32
TIMEOUT 600
ONTIMEOUT BootLocal
PROMPT 0
MENU TITLE My PXE Server (by TORNADO)
ALLOWOPTIONS 1
menu width 80
menu rows 15
MENU TABMSGROW 24
MENU MARGIN 10
NOESCAPE 1
LABEL BootLocal
localboot 0
TEXT HELP
Boot to local hard disk
ENDTEXT
LABEL UBUNTU_1204_DISKLESS
MENU LABEL Ubuntu 12.04 (64-bit) DISKLESS
KERNEL Ubuntu/12.04/x86_64/vmlinuz-3.2.0-20-generic
APPEND root=/dev/nfs nfsroot=192.168.1.10:/srv/nfsroot/Ubuntu/12.04/x86_64,ro initrd=Ubuntu/12.04/x86_64/initrd.img-3.2.0-20-generic ip=dhcp aufs=tmpfs
TEXT HELP
Boot the Ubuntu 12.04 64-bit Diskless
ENDTEXT
EOF
III. NFS
1. Install nfs
# yum install nfs-utils
# chkconfig nfs on
# service nfs start
2. Add /srv/nfsroot to exports
# cat << EOF > /etc/exports
/srv/nfsroot *(ro,async,no_root_squash,no_subtree_check,no_all_squash)
EOF
3. Apply exports
# exportfs -r
IV. Prepare installation
1. Install Ubuntu
Generally you have two ways.
- Use debootstrap.
I used this option to prepare some tiny installations (like network boot for number of POS terminals).
- Install the Ubuntu on the real or virtual system and copy it to NFS server.
In this article I will follow this way, because I want to prepare a usual Ubuntu installation.
After system was installed and configured as you want, you need to prepare it for network boot.
2. Modify /etc/network/interfaces to set eth0 configuration type to manual:
iface eth0 inet manual
3. Configure /etc/fstab to be looking like this:
# /etc/fstab: static file system information.
#
#
proc /proc proc defaults 0 0
/dev/nfs / nfs defaults 1 1
4. Change the following options in /etc/initramfs-tools/initramfs.conf:
MODULES=netboot
BOOT=nfs
DEVICE=eth0
NOTE: If the client source installation you copied the
files from should remain bootable and usable from local hard disk,
restore the former BOOT=local and MODULES=most options you changed in
/etc/initramfs-tools/initramfs.conf. Otherwise, the first time you
update the kernel image on the originating installation, the initram
will be built for network boot, giving you "can't open
/tmp/net-eth0.conf" and "kernel panic". Skip this step if you no longer
need the source client installation.
5. Add to /etc/initramfs-tools/modules line:
aufs
6. Copy aufs module to /etc/initramfs-tools/scripts/modules
$ sudo cp /lib/modules/$(uname -r)/kernel/ubuntu/aufs/aufs.ko /etc/initramfs-tools/scripts/modules
7. Copy the following script to /etc/initramfs-tools/scripts/init-bottom as 00_aufs_init (0755):
#!/bin/sh -e
case $1 in
prereqs)
exit 0
;;
esac
for x in $(cat /proc/cmdline); do
case $x in
root=*)
ROOTNAME=${x#root=}
;;
aufs=*)
UNION=${x#aufs=}
case $UNION in
LABEL=*)
UNION="/dev/disk/by-label/${UNION#LABEL=}"
;;
UUID=*)
UNION="/dev/disk/by-uuid/${UNION#UUID=}"
;;
esac
;;
esac
done
echo "Union=$UNION"
if [ -z "$UNION" ]; then
exit 0
fi
modprobe -b aufs && echo "OK: modprobe -b aufs" || echo "ERR: modprobe -b aufs"
# make the mount points on the init root file system
mkdir /aufs /ro /rw && echo "OK: mkdir /aufs /ro /rw" || echo "ERR: mkdir /aufs /ro /rw"
# mount read-write file system
if [ "$UNION" = "tmpfs" ]; then
mount -t tmpfs rw /rw -o noatime,mode=0755 && echo "OK: mount -t tmpfs rw /rw -o noatime,mode=0755 " || echo "ERR: mount -t tmpfs rw /rw -o noatime,mode=0755"
else
mount $UNION /rw -o noatime
fi
# move real root out of the way
mount --move ${rootmnt} /ro && echo "OK: mount --move ${rootmnt} /ro" || echo "ERR: mount --move ${rootmnt} /ro"
mount -t aufs aufs /aufs -o noatime,dirs=/rw:/ro=ro && echo "OK: mount -t aufs aufs /aufs -o noatime,dirs=/rw:/ro=ro" || echo "ERR: mount -t aufs aufs /aufs -o noatime,dirs=/rw:/ro=ro"
# test for mount points on union file system
[ -d /aufs/ro ] || mkdir /aufs/ro
[ -d /aufs/rw ] || mkdir /aufs/rw
mount --move /ro /aufs/ro && echo "OK: mount --move /ro /aufs/ro" || echo "ERR: mount --move /ro /aufs/ro"
mount --move /rw /aufs/rw && echo "OK: mount --move /rw /aufs/rw" || echo "ERR: mount --move /rw /aufs/rw"
# strip fstab off of root partition
grep -v $ROOTNAME /aufs/ro/etc/fstab > /aufs/etc/fstab
mount --move /aufs /root && echo "OK: mount --move /aufs /root" || echo "ERR: mount --move /aufs /root"
exit 0
To be honest this script isn't mine. I found it some time ago and I don't remember where. If you are the author or you know who he is, please tell me in comments so I put your name here.
8. Build a new initrd image:
$ sudo update-initramfs -k $(uname -r) -c -b /root/
9. Now you can copy this all on server by executing the following command on
client:
$ sudo rsync -a --exclude=tmp/* --exclude=proc/* --exclude=sys/* --exclude=dev/* / username@192.168.1.10:/srv/nfsroot/Ubuntu/12.04/x86_64/
Be careful with all slashes! rsync treats source or destination in different way if slash is omitted.
"username" must have write permissions to /srv/nfsroot/Ubuntu/12.04/x86_64.
10. Copy kernel and new initrd image to a proper folder on tftp. Run it
ON THE SERVER
# cp /srv/nfsroot/Ubuntu/12.04/x86_64/boot/vmlinuz-$(uname -r) username@192.168.1.10:/tftpboot/Ubuntu/12.04/x86_64/
# cp /srv/nfsroot/Ubuntu/12.04/x86_64/root/initrd.img-$(uname -r) username@192.168.1.10:/tftpboot/Ubuntu/12.04/x86_64/
Notes
Remember, that changes to the root filesystem is limited by you RAM. This means that you will not be able to copy a 4GB video to /tmp if you have only 2GB of RAM.
I have prepared this post without access to my test environment, so some small mistakes are possible. If you find any, please comment.
