Linux startup sequence

BIOS

• System startup

Stage 1 boot loader

• MBR

Stage 2 boot loader

• GRUB - /boot/grub
• Loads kernel - /boot/vmlinuz
• Runs kernel - startup_32()

Kernel

• Runs non-architecture kernel - start_kernel()
• Loads initial ramdisk - /boot/initrd.img
• Loads driver modules - /lib/modules
• Loads root filesystem
• Runs /sbin/init

Init

• Reads /etc/inittab
• Reads /etc/event.d
• Runs default run level

Run levels

• /etc/rc0.d System halt
• /etc/rc1.d Single user
• /etc/rc2.d Full multi-user (default)
• /etc/rc3.d Full multi-user
• /etc/rc4.d Full multi-user
• /etc/rc5.d Full multi-user
• /etc/rc6.d System reboot

Mount filesystems

• /proc
• /sys