Book: LPI Linux Certification in a Nutshell Section: Chapter 10. Exam 101 Highlighter's Index
### 10.3 Boot, Initialization, Shutdown, and Runlevels (Topic 2.6) #### 10.3.1 Objective 1: Boot the System ##### 10.3.1.1 LILO, the Linux loader LILO is a utility designed to load a Linux kernel (or another operating system) into memory and launch it. It has two parts: The boot loader. A two-stage program intended to find and load a kernel. The first stage resides in the disk boot sector and is started by the system BIOS. It locates and launches a second, larger stage residing elsewhere on disk. The lilo command The map installer, used to install and configure the LILO boot loader. It reads /etc/lilo.conf and writes a corresponding map file. The /etc/lilo.conf file contains options and kernel image information. Popular directives are: boot The name of the hard disk partition that contains the boot sector. image Refers to a specific kernel file. install The file installed as the new boot sector. label Provides a label, or name, for each `image`. map Directory where the map file is located. prompt Prompts the user for input (such as kernel parameters or runlevels) before booting and without a keystroke from the user. read-only The root filesystem should initially be mounted read-only. root Used following each `image`, this specifies the device that should be mounted as root. timeout The amount of time, in tenths of a second, the system waits for user input. ##### 10.3.1.2 Kernel parameters and module configuration LILO can pass kernel parameters using name=value pairs. Linux kernels are modular, with portions of kernel functionality compiled as modules to be used as needed. Parameters to modules can be specified in /etc/conf.modules. ##### 10.3.1.3 Boot-time messages The kernel gives detailed status information as it boots. This information can also be found in system logs such as /var/log/messages and from the dmesg command. #### 10.3.2 Objective 2: Change Runlevels and Shutdownor Reboot System Runlevels specify how a system is used by controlling which services are running. Runlevels are numbered through 6, as well as with a few single characters. Runlevel 0 implies system shutdown. Runlevel 6 implies system reboot. The intermediate runlevels differ in meaning among distributions. Runlevel 1 (also s or S) is usually single-user (maintenance) mode. Runlevels 2 through 5 usually define some kind of multiuser state, including an X login screen. ##### 10.3.2.1 Single-user mode Runlevel 1 is a bare-bones operating environment intended for maintenance. Remote logins are disabled, networking is disabled, and most daemons are shut down. Single-user mode can be entered with the single, or simply 1, parameter at the LILO prompt. Switching to single-user mode is done using init 1. ##### 10.3.2.2 The /etc/rc.d directory The /etc/rc.d file contains initialization scripts and links controlling the boot process for many Linux distributions: rc.sysinit The startup script launched by init at boot time. rc.local A script for local startup customizations, started automatically after the system is running. rc A script used to change runlevels. init.d The directory containing scripts to start and stop system services. rc0.d through rc6.d Links to scripts in init.d. Names of the links are [K|S][nn][init.d_name]: K and S prefixes mean kill and start, respectively. nn is a sequence number controlling startup or shutdown order. init.d_name is the name of the script being linked. ##### 10.3.2.3 Default runlevel, determining runlevel, changing runlevels The default runlevel is located in /etc/inittab on the line containing initdefault: id:n:initdefault: n is a valid runlevel number such as 3. Runlevel is determined by the runlevel command, which displays the previous and current runlevels. An N for previous runlevel indicates that the runlevel has not changed since startup. Runlevels can be changed using init: init n Change to runlevel n. System shutdown can also be initiated using shutdown: shutdown time Bring the system down in a secure, organized fashion. time is mandatory, in the form of hh:mm, now, or +n for n minutes.