Linux booting

How does it work?

First the bootloader

• The first step is for the bootloader to run

• BIOS indicates what devices to examine

• Bootstrap program looks on each of the devices indicated for a boot loader– Lilo– Grub

• Configuration files for booting in /boot

Bootloader

• Kernel image is in /boot

• Reconfiguring lilo requires running the lilo command in order to rewrite the boot info. (similarly for grub)

• Mounts file system

Mounting file system

• /etc/fstab

• Contains configuration to tell loader how to mount the file systems– What device– What directory to mount to– Type of file system

/dev/hdb8/varext3

/dev/hdb1 / ext3 defaults 1 1/dev/hdb8 /var ext3 defaults 1 2…

init (the first process)• Executed after mounting file systems

• Configures itself by /etc/inittab• Run level -> which scripts to run at startup

# 3 - Full multiuser mode# 4 - unused# 5 - X11# 6 - reboot (Do NOT set initdefault to this)# id:3:initdefault:

First rc script – rc.sysinit

• Executes some of the scripts in /etc/sysconfig including network– Defines relevant environment variables

• Lots of other scripts

• Messages seen during boot process

Next rc scripts

• /etc/rc.d/rc 3– To run at level 3

• Does things like checking for the existence of the run files for that level

• Invokes the right ones

• “rc 3” -> run scripts in /etc/rc.d/rc3.d

rc3.d scriptsK09dm@ S15gpm@ S26ypxfrd@ S56xinetd@ S85numlock@ S92lisa@K90mysql@ S16ypserv@ S31upsmon@ S60cups@ S85proftpd@ S95kheader@S08ipvsadm@ S17alsa@ S40atd@ S60nfs@ S89internet@ S99devfsd@S10network@ S18sound@ S40saslauthd@ S60rwhod@ S90crond@ S99linuxconf@S11portmap@ S20random@ S55named@ S66yppasswdd@ S90postgresql@ S99local@S12syslog@ S20xfs@ S55ntpd@ S75keytable@ S90squid@ S99mysql@S13partmon@ S25netfs@ S55sshd@ S80postfix@ S90webmin@S14nfslock@ S26apmd@ S56rawdevices@ S85httpd@ S91smb@

lrwxr-xr-x 1 root root 17 Oct 23 2002 S10network -> ../init.d/network*

•All scripts are actually in /etc/rc.d/init.d and linked to these.•K is used when killing•S is used as a startup script•Numerical value says order in which to run•Example: S10network says to run /etc/rc.d/init.d/network when starting up the system immediately after launching ipvsadm

Example script network…case “$1” in start) … restart)

… stop) …

/etc/rc.d/init.d/network

[root@testmachine] init.d% ./network restart

Runs the scripts with restart option

dmesgdmesgLinux version 2.4.19-16mdk (quintela@bi.mandrakesoft.com) (gcc version 3.2 (Mandrake Linux 9.0 3.2-1mdk)) #1 Fri Sep 20 18:15:05BIOS-provided physical RAM map: BIOS-e820: 0000000000000000 - 0000000000080000 (usable) BIOS-e820: 000000000009fc00 - 00000000000a0000 (reserved) BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved) BIOS-e820: 0000000000100000 - 0000000005fec000 (usable) BIOS-e820: 0000000005fec000 - 0000000005fef000 (ACPI data) BIOS-e820: 0000000005fef000 - 0000000005fff000 (reserved) BIOS-e820: 0000000005fff000 - 0000000006000000 (ACPI NVS) BIOS-e820: 00000000fec00000 - 00000000fec01000 (reserved) BIOS-e820: 00000000fee00000 - 00000000fee01000 (reserved) BIOS-e820: 00000000ffff0000 - 0000000100000000 (reserved)95MB LOWMEM available.Advanced speculative caching feature not presentOn node 0 totalpages: 24556zone(0): 4096 pages.zone(1): 20460 pages.zone(2): 0 pages.Kernel command line: BOOT_IMAGE=linux ro root=341 quiet devfs=mountFound and enabled local APIC!Initializing CPU#0Detected 929.225 MHz processor.Console: colour dummy device 80x25…