Chapter 8. The LRP Boot Process

Table of Contents

Linux Kernel

Booting LRP is where many of the differences of the different LRP variants appear. The basics are the same, however. The following steps take place:


  1. The master boot record of the floppy is loaded by the computer's BIOS. This is part of syslinux.

  2. The configuration file syslinux.cfg is read and acted upon. This includes differing kernel options and images, text screen displays, help screens, and so on.

  3. The filesystem image is loaded — in the case of LRP, this is root.lrp.

  4. The appropriate kernel image is loaded — for LRP, this is the file linux.

Linux Kernel [15]

  1. The Linux kernel is decompressed and executed.

  2. The filesystem image (root.lrp) is decompressed and loaded. A kernel patch allows a compressed filesystem here. The kernel parameter ROOT is refered to here; if it is not set right, Linux will stop with a Kernel panic: VFS: Unable to mount root fs message, since it can't find the appropriate filesystem on that disk if ROOT is specified wrong (or if the internal value of ROOT is wrong).

  3. The shell script /linuxrc is run. In most versions of LRP, this is a symbolic link to /var/lib/lrpkg/root.linuxrc The kernel patch linuxrc-always makes /linuxrc always run, instead of only when the boot-time root volume is /dev/ram0 and the true root device is different... [16]


  1. From here, the differing versions vary widely — typical tasks performed by /linuxrc include:

    • Load packages from disk or TFTP or other method

    • Load kernel modules

    • Bring up network interfaces using DHCP or other method

    • Create device special files in /dev

    • Create links to busybox and POSIXness (for various commands)

    • Create RAM disks (such as for /var/log or /tmp)


  1. Finally, /sbin/init is run by the Linux kernel, once /linuxrc is complete. /sbin/init scans through the /etc/inittab , performing actions as necessary...

  2. The /etc/init.d/rcS file is run by init, and loads the startup elements for LRP. The rcS file is specified in /etc/inittab in a line like: si::sysinit:/etc/init.d/rcS

  3. The /etc/init.d/rc file is run for the appropriate run level (given as argument 1). The rc file is specified in /etc/inittab in lines like:

    l0:0:wait:/etc/init.d/rc 0
    l1:1:wait:/etc/init.d/rc 1
    l2:2:wait:/etc/init.d/rc 2
    l3:3:wait:/etc/init.d/rc 3
    l4:4:wait:/etc/init.d/rc 4
    l5:5:wait:/etc/init.d/rc 5
    l6:6:wait:/etc/init.d/rc 6
  4. /sbin/getty is normally run as part of the processing of init, providing a way to log into the system. getty takes care of both serial consoles and virtual consoles (though these could be two different kinds of gettys). getty is usually specified in lines like:

    1:2345:respawn:/sbin/getty 38400 tty1
    1:23:respawn:/sbin/getty 38400 tty2
    1:23:respawn:/sbin/getty 38400 tty3
    1:23:respawn:/sbin/getty 38400 tty4
    1:23:respawn:/sbin/getty 38400 tty5


  1. The rc (or rcS) file is run as an important part of the init startup procedure. These files read everything in /etc/rc*.d and /etc/rcS.d, and run the programs linked to in order. These programs start system daemons such as portsentry, cron, httpd, ftpd, and others.


  1. The getty program is run from init. It normally runs login, which verifies the password and username from the user, then runs whatever shell is specified in /etc/passwd.

[15] Booting the kernel is more complicated than this; in trying to use the standard boot sequence (without LRP patches) one needs to understand the Linux kernel boot process more fully. This is covered in a later section.

[16] See the later section on using a kernel without LRP patches for more details.