12. Redhat Linux configuration

The DC requests to mount /tftpboot/< IP address of DC > (in Linux Kernel 2.1 and above it is - /tftpboot/< name of DC in bootptab > ) as its root directory '/' by NFS from server. You must export this from the server (rw, no_root_squash) because the DC wants to write on it (log files, etc).

The root directory / must contain /sbin, /bin, /lib, /etc, /var, /tmp, /root, /dev and /proc.

/sbin, /bin, /lib can be a copy of an existing Redhat Linux system. They can be shared between all DCs. But hard links only. By the way, don't link to server originals.

/etc, /var and /dev should be non-sharable copies. Customise /etc/sysconfig/network, /etc/sysconfig/network-scripts/ifcfg-eth0, /etc/fstab, /etc/conf.modules, and others. Turn off all network services you don't need. Remove all stuff you don't need from /var, e.g. RPM db, lpd files.

/root and /proc should just exist. /tmp should exist and be mode 1777.

You probably want to create /usr and /home mount points. /usr can be mounted ro (read-only).

About 10 MB per DC plus about 15 MB of shared files should be sufficient. By the way, if your DCs are quite similar, the kernel image can also be shared.

Here is an illustrative script to create the first root filesystem.

#!/bin/sh
if [ $# != 1 ]
then
        echo Usage: $0 client-IP-addr
        exit 1
fi

cd /

umask 022

mkdir -p /tftpboot/$1

# just make these ones
for d in home mnt proc tmp usr
do
        mkdir /tftpboot/$1/$d
        done

        chmod 1777 /tftpboot/$1/tmp

        touch /tftpboot/$1/fastboot
        chattr +i /tftpboot/$1/fastboot

        # copy these ones
        cp -a bin lib sbin dev etc root var /tftpboot/$1

cat <<EOF
Now, in /tftpboot/$1/etc, edit

                sysconfig/network
                sysconfig/network-scripts/ifcfg-eth0
                fstab
                conf.modules

and configure

                rc.d/rc3.d
EOF

Here is an illustrative script to duplicate the root filesystem

#!/bin/sh
if [ $# != 2 ]
then
        echo Usage: $0 olddir newdir
        exit 1
fi

cd /tftpboot

if [ ! -d $1 ]
then
        echo $1 is not a directory
        exit 1
fi

umask 022

mkdir -p $2

# just make these ones
for d in home mnt proc tmp usr
do
        mkdir $2/$d
done

chmod 1777 $2/tmp

touch $2/fastboot
chattr +i $2/fastboot

# link these ones
for d in bin lib sbin
do
        (cd $1; find $d -print | cpio -pl ../$2)
done

# copy these ones
for d in dev etc root var
do
        cp -a $1/$d $2
done

cat <<EOF
Now, in /tftpboot/$2/etc, edit

        sysconfig/network
        sysconfig/network-scripts/ifcfg-eth0
        fstab (maybe)
        conf.modules (maybe)

and configure

        rc.d/rc3.d
EOF

12.1 X-terminal

On the server, make sure the DC is matched by a clause in /etc/X11/xdm/Xaccess and comment out the :0 in /etc/X11/xdm/Xservers. Then make sure that xdm is run from the init scripts.

On the client, run X -query server

You will get the xdm login box and then all your X clients will run on the server.

For other applications use - you could use diskless technique for netboot routers, print servers (but should not be spooling print server), standalone apps, etc.