1. Unix kernel Kernel refers to the core part of an operating system Historically, UNIX kernels are monolithic Newer versions of UNIX allow part of the kernel to be loaded on demand (called loadable kernel modules)

2. Booting FreeBSD on a PC Power-on self test (POST) BIOS loads the first-stage bootstrap loader from the master boot record (MBR) in the boot device to RAM and executes it The first-stage boot loader loads the subsequent boot loaders, which in term load the kernel

3. Bootstrap Steps (cont.) Load & initialize kernel Detect & configure devices Create spontaneous system processes Operator intervention Execute system startup scripts Multiuser mode

4. Booting FreeBSD 4.8 Use dmesg|more to read boot time messages (these messages are printed in brighter characters) Enter single user mode after init and other processes are created and after device configuration

5. Single User Mode Lets operator manually fix errors and control booting progress Do a “ ps ax ” right after entering single user mode to see how many processes exist in the system Exiting the single user shell resumes normal booting steps

6. Startup scripts /etc/rc is the main startup script All configurable setting are placed in /etc/rc.conf Take a look at /etc/rc and other related rc.* files to learn how to read and write shell scripts