Linux Administration/System Architecture/Boot Sequence
This lesson covers the boot sequence.
Objectives and Skills
editObjectives and skills for the boot sequence portion of Linux+ certification include:[1]
- Boot the system
- Provide common commands to the boot loader and options to the kernel at boot time
- Demonstrate knowledge of the boot sequence from BIOS to boot completion
- Understanding of SysVinit and systemd
- Awareness of Upstart
- Check boot events in the log file
- The following is a partial list of the used files, terms and utilities:
- dmesg
- BIOS
- bootloader
- kernel
- initramfs
- init
- SysVinit
- system
Readings
editMultimedia
editActivities
edit- Complete the tutorial IBM: Learn Linux, 101: Boot the system
- Use the GRUB boot menu.
- Access the GRUB menu. Review available options and advanced options.
- Edit one of the GRUB menu items to see the configuration but do not make any changes.
- Access the command line. Use the
reboot
command to reboot the system. - Review Ubuntu: RecoveryMode. Boot into Recovery mode and review available options. Reboot the system.
- List the steps in the boot sequence from BIOS to boot completion.
- Identify which major Linux distributions use or used init, SysVInit, systemd, and Upstart.
- Compare the contents of
/var/log/kern.log
with the output fromdmesg
.
Lesson Summary
edit- The boot sequence includes ROM, Power-On Self-Test (POST), boot manager, boot loader, and user software or graphical user interface (GUI).[2]
- A master boot record (MBR) is a special type of boot sector at the very beginning of partitioned computer mass storage devices like fixed disks or removable drives intended for use with IBM PC-compatible systems and beyond.[3]
- Boot loaders interact with the BIOS to load the operating system.[4]
- System V SysVinit startup is based on runlevels. SysVinit runlevels include:[5]
- 0 - Shutdown
- 1 - Single-user mode
- 2 - Multi-user mode
- 3 - Multi-user mode with RFS
- 4 - Multi-user mode, User-definable
- 5 - Halt
- 6 - Reboot
- S - Single-user mode with terminal console
- Upstart is an event-based replacement for the traditional init daemon.[6]
- Upstart was the default init system in Ubuntu and Chrome OS.[7]
- systemd is now the default init system in most Linux distributions, [8] including RHEL and Ubuntu.
- GRUB boot options include a list of operating systems, "e" to edit the list, and "c" for a command-line.[9]
- GRUB recovery mode provides a Recovery Menu of options.[10]
- dmesg (display message or driver message) is a command on most Unix-like operating systems that prints the message buffer of the kernel.[11]
Key Terms
edit- ELILO (EFI Linux Loader
- EFI/UEFI boot loader[12]
- GRUB (GRand Unified Bootloader)
- A boot loader package from the GNU Project.[13]
- initramfs (initial RAM file system)
- A scheme for loading a temporary root file system into memory.[14]
- initrd (initial ramdisk)
- A scheme for loading a temporary root file system into memory.[15]
References
edit- ↑ CompTIA: Linux+ Certification Exam Objectives - Exam LX0-103
- ↑ Wikipedia: Booting
- ↑ Wikipedia: Master boot record
- ↑ Wikipedia: Booting
- ↑ Wikipedia: init
- ↑ Wikipedia: Upstart (software)
- ↑ Wikipedia: Upstart (software)
- ↑ Wikipedia: Upstart (software)
- ↑ [[Wikipedia: GNU GRUB]]
- ↑ Wikipedia: GNU GRUB
- ↑ Wikipedia: dmesg
- ↑ Wikipedia: LILO (boot loader)
- ↑ Wikipedia: GNU GRUB
- ↑ Wikipedia: Initial ramdisk
- ↑ Wikipedia: Initial ramdisk