Directory structure

As seen in chapter two, the make install of busybox has created some directories containing dozens of symlinks. We've only created two directories: /dev/pts and /proc.

Now, it's time to set up all the other needed directories.

$ cd /home/christian/Dreamcast
$ cd INITRD
$ ls
bin dev etc linuxrc proc sbin usr
$

The Filesystem Hierarchy Standard proposes the following directories:

• /bin Essential user command binaries (for use by all users). For example, our /bin contains cp, df, rm,...

• /boot Static files of the boot loader. We don't need this directory due to the use of a sh-specific, external bootloader.

• /dev Device files. Here, we create all device nodes, we need to communicate with the kernel.

• /etc Host-specific system configuration. This folder will contain the configuration files, such as passwd, inittab among others.

• /home User home directories (optional). We'll create this directory "on the fly", i.e. if the user plugs in the VMU.

• /lib Essential shared libraries and kernel modules. This directory will only contain the kernel modules caused by the lack of a dynamic loader for dynamic libraries.

• /mnt Mount point for a temporarily mounted filesystem. We need this folder for mounting the VMU.

• /opt Add-on application software packages. We don't need this folder.

• /root Home directory for the root user (optional). We create this directory for the super user.

• /sbin System binaries. This directory contains essential system software, such as insmod, ifconfig and others.

• /tmp Temporary files.

• /usr/bin Most user commands. This Folder contains cut, du,...

• /usr/sbin Non-essential standard system binaries. This folder will contain sshd and other service tools.

• /var/lib Variable state information. This directory will contain files about DHCP.

• /var/log Log files and directories. This folder contains logging information.

• /var/run Run-time variable data. Here, some process create some kind of "cookies", often their process id.

As you notice, we don't cover all proposed directories due to the limited amount of free inodes.

Let's go and create all needed directories and configuration files. Remember, that you've chown'ed all files to the super user, so change your user userid to the super user:

$ su
#

1. /dev

   First, we create the device nodes and set up their mode and ownership:

   # cd dev
   
   # chmod 600 console
   # chown 0.1 console
   
   # mknod gdrom0 b 250 0
   # chmod 640 gdrom0
   # chown 0.2 gdrom0
   
   # mknod mtdblock0 b 31 0
   # chmod 660 mtdblock0
   # chown 0.2 mtdblock0
   
   # mknod null c 1 3
   # chmod 666 null
   # chown 0.0 null
   
   # mknod ppp c 108 0
   # chmod 660 ppp
   # chown 0.3 ppp
   
   # mknod ptmx c 5 2
   # chmod 666 ptmx
   # chown 0.1 ptmx
   
   # mknod random c 1 8
   # chmod 666 random
   # chown 0.0 random
   
   # mknod tty c 5 0
   # chmod 600 tty
   # chown 0.0 tty
   
   # mknod tty0 c 4 0
   # chmod 600 tty0
   # chown 0.0 tty0
   
   # mknod tty1 c 4 1
   # chmod 600 tty1
   # chown 0.0 tty1
   
   # mknod tty2 c 4 2
   # chmod 600 tty2
   # chown 0.0 tty2
   
   # mknod tty3 c 4 3
   # chmod 600 tty3
   # chown 0.0 tty3
   
   # mknod tty4 c 4 4
   # chmod 600 tty4
   # chown 0.0 tty4
   
   # mknod ttySC0 c 204 8
   # chmod 600 ttySC0
   # chown 0.3 ttySC0
   
   # mknod ttySC1 c 204 9
   # chmod 600 ttySC1
   # chown 0.3 ttySC1
   
   # mknod urandom c 1 9
   # chmod 444 urandom
   # chown 0.0 urandom
   
   # mknod zero c 1 5
   # chmod 666 zero
   # chown 0.0 zero
   
   # cd ..
   

   As you notice, we've set different group ids. These ids have to correspond with our entries in /etc/group later.

2. /etc

   This directory comprises the configuration files. So, be careful with your entries and chmodes!

   # cd etc
   
   # cat <<. >group
   root:x:0:
   tty:x:1:
   disk:x:2:
   dip:x:3:
   shadow:x:4:
   .
   # chmod 644 group
   
   # cat <<. >gshadow
   root:*::
   tty:!::
   disk:!::
   dip:!::
   shadow:!::
   .
   # chmod 640 gshadow
   # chown 0.4 gshadow
   
   # cat <<. >hosts
   127.0.0.1       localhost
   192.168.1.1     dreamcast.localdomain  dreamcast
   .
   # chmod 640 hosts
   
   # mkdir init.d
   # cd init.d
   cat <<. > rcS
   #!/bin/sh
   
   PATH=/bin:/sbin:/usr/bin:/usr/sbin
   
   echo "Mounting /proc filesystem..."
   mount -t proc none /proc
   
   echo "Mounting /dev/pts filesystem..."
   mount -t devpts none /dev/pts
   
   echo "Loading eth0 module..."
   modprobe lan_adapter
   modprobe mii
   modprobe 8139too
   
   echo "Loading mtd modules..."
   modprobe mtdcore          2>&1 > /dev/null
   modprobe mtdblock         2>&1 > /dev/null
   modprobe chipreg          2>&1 > /dev/null
   modprobe vmu-flash        2>&1 > /dev/null
   
   echo "Loading netfilter modules..."
   for mod in ip_conntrack ip_conntrack_ftp \
    ip_conntrack_irc ip_tables iptable_filter \
    iptable_nat ipt_limit ipt_state ip_nat_ftp \
    ip_nat_irc ipt_LOG ipt_MASQUERADE;
   do
      modprobe $mod 2>&1 > /dev/null
   done
   
   echo "Setting up routing..."
   iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
   echo 1 > /proc/sys/net/ipv4/ip_forward
   
   echo "Setting hostname..."
   hostname dreamcast
   
   echo "Configuring lo..."
   ifconfig lo 127.0.0.1 up
   
   echo "Configuring eth0..."
   ifconfig eth0 192.168.1.1 up
   
   echo "Starting klogd..."
   klogd
   
   echo "Starting syslogd..."
   syslogd
   
   #echo "Starting udhcpd..."
   #udhcpd
   
   #echo "Starting yaku-ns..."
   #/usr/yaku-ns/yaku-ns -c \
   # /usr/yaku-ns/yaku-ns.conf -l \
   # /usr/yaku-ns/yaku-ns.log -u yaku -d
   
   #echo "Starting sshd..."
   #sshd -f /etc/ssh/sshd_config
   
   /bin/sleep 1
   
   echo "Everything's done. Have fun."
   .
   # chmod 744 rcS
   

   The file /etc/init.d/rcS starts all initial services. As you notice, some services are disabled by # because we haven't compiled them yet.

   # cd ..
   # cat <<. >inittab
   # Initial startup file
   
   ::once:/etc/init.d/rcS
   
   # Start four ask first login prompts
   tty1::askfirst:/bin/login
   tty2::askfirst:/bin/login
   tty3::askfirst:/bin/login
   tty4::askfirst:/bin/login
   
   ::ctrlaltdel:/sbin/reboot
   
   .
   # chmod 644 inittab
   
   # cat <<. >passwd
   root:x:0:0:root:/root:/bin/sh
   .
   # chmod 644 passwd
   
   # cat <<. >shadow
   root:*:12091:0:99999:7:::
   nobody:*:12091:0:99999:7:::
   .
   # chmod 640 shadow
   # chown 0.4 shadow
   

   The shadow and passwd contain the usernames and passwords. If you need the same usernames and passwords like your host, just copy the files /etc/passwd, /etc/shadow, /etc/gshadow and /etc/group to your initial ramdisk.

   # mkdir ppp
   
   # touch resolv.conf
   # chmod 644 resolv.conf
   
   # cat <<. >services
   tcpmux      1/tcp              # TCP port service multiplexer
   echo        7/tcp
   echo        7/udp
   ftp-data    20/tcp
   ftp         21/tcp
   fsp         21/udp  fspd
   ssh         22/tcp             # SSH Remote Login Protocol
   ssh         22/udp             # SSH Remote Login Protocol
   telnet      23/tcp
   smtp        25/tcp  mail
   domain      53/tcp  nameserver # name-domain server
   domain      53/udp  nameserver
   www         80/tcp  http       # WorldWideWeb HTTP
   www         80/udp             # HyperText Transfer Protocol
   pop3        110/tcp pop-3      # POP version 3
   pop3        110/udp pop-3
   ntp         123/tcp
   ntp         123/udp            # Network Time Protocol
   
   .
   # chmod 644 services
   
   # mkdir ssh
   
   # cd ..
   

   Now, you have a correct configure /etc - directory.

3. /home

   # mkdir /home

4. /mnt

   # mkdir /mnt

5. /root

   # mkdir root
   # chmod 700 root
   

6. /tmp

   # mkdir /tmp

7. /var/lib

   # mkdir -p /var/lib

8. /var/log

   # mkdir /var/log

9. /var/run

   # mkdir /var/run

Now, you've got a proper set up initial ramdisk directory layout.