Linux Administration/System Architecture/Boot Configuration

This lesson covers boot configuration.

Objectives and Skills

Objectives and skills for the boot sequence portion of Linux+ certification include:

• Change runlevels/boot targets and shutdown or reboot system.
  • Set the default runlevel or boot target
  • Change between runlevels/boot targets including single user mode
  • Shut down and reboot from the command line
  • Alert users before switching runlevels/ boot targets or other major system events
  • Properly terminate processes
  • The following is a partial list of the used files, terms and utilities:
    • /etc/inittab
    • shutdown
    • init
    • /etc/init.d
    • telinit
    • system
    • systemctl
    • /etc/systemd/
    • /usr/lib/system/
    • wall

Readings

1. Wikipedia: Runlevel
2. Wikipedia: Shutdown (computing)
3. Wikipedia: init
4. systemd
5. Wikipedia: Upstart (software)
6. Wikipedia: wall (Unix)

Multimedia

1. YouTube: Working with Linux Runlevels
2. YouTube: Properly Terminating Linux Processes
3. YouTube: Init, Systemd, and Upstart

Activities

1. Complete the tutorial IBM: Learn Linux, 101: Runlevels, boot targets, shutdown, and reboot
2. Shutdown
   • Use shutdown to shutdown the system.
   • Use telinit 0 to shutdown the system.
   • Use systemctl isolate poweroff.target to shutdown the system.
3. Reboot
   • Use reboot to reboot the system.
   • Use telinit 6 to reboot the system.
   • Use systemctl isolate reboot.target to reboot the system.
   • Use telinit 1 to reboot the system in single-user mode.
   • Use systemctl isolate rescue.target to reboot the system in single-user mode.
4. Test the difference between halt and halt -p.
5. Set default runlevels.
   • Use systemctl set-default multi-user.target to configure multi-user mode. Reboot.
   • Use systemctl set-default graphical.target to configure graphical user mode. Reboot.
6. Review HowToForge: Linux wall Command Tutorial. Use wall to alert users of an impending reboot.
7. Use kill to stop processes.
   • Review Benjamin Cane: Understanding the kill command, and how to terminate processes in Linux.
   • Run a user program, such as the calculator or an editor. Use ps -A to find the program's process ID. Use kill and the process ID to ask the program to terminate itself.
   • Run the program. Use ps -A to find the program's process ID. Use kill -15 and the process ID to ask the program to terminate itself.
   • Run the program. Use ps -A to find the program's process ID. Use kill -SIGTERM and the process ID to ask the program to terminate itself.
   • Run the program. Use ps -A to find the program's process ID. Use kill -9 and the process ID to kill the process.
   • Run the program. Use ps -A to find the program's process ID. Use kill -SIGKILL and the process ID to kill the process.
8. Stop and restart services.
9. Review CyberCiti.biz: Service command.
   • Use service --status-all to list service status.
   • Use service cups stop to stop the printing service.
   • Use service cups start to start the printing service.
   • Use service cups restart to restart the printing service.

Lesson Summary

• The halt command will halt, poweroff, or reboot the system:
  • halt command stops CPU processing
  • halt -p stops CPU processing and powers off a system
  • halt --reboot reboots a system
• The kill command is used to terminate processes without having to log out or reboot the computer.
  • kill <pid> (SIGTERM, option 15) and signals the process to terminate itself
  • kill -9 <pid> or kill -SIGKILL <pid> kills the process
• The service command is used to start, stop, and restart services.
• The shutdown command turns off or reboots a computer.
  • shutdown -h now shuts down a system immediately
  • shutdown -r now reboots a system
• The systemctl command is used to examine and control the state of "systemd".
  • systemctl isolate <target> changes the runlevel
  • systemctl set-default <target> sets the default runlevel
• systemctl runlevels include:
  • 0 - poweroff.target
  • 1 - rescue.target
  • 3 - multi-user.target
  • 5 - graphical.target
  • 6 - reboot.target
• The telinit command signals init to change runlevels. Runlevels include:
  • 0 - halt
  • 1 - single-user mode
  • 6 - reboot
• The wall command (write to all) displays the contents of a file or standard input to all logged-in users.
• /etc/init.d contains start/stop scripts for system services.
• /etc/inittab is the top-level configuration file for init.
• /etc/systemd/ contains local systemd configuration files.

See Also

• Linux.com: Understanding and Using Systemd

References

← Boot Sequence

Linux Administration/System Architecture