Managing Runlevels and Boot Targets with SysVinit and Systemd #

In this tutorial, we’ll cover the key aspects of changing runlevels, boot targets, shutting down, and rebooting a system for the LPIC-1 exam. We’ll explore both SysVinit and systemd, including setting default runlevels/boot targets, alerting users, and properly terminating processes.

1. Setting the Default Runlevel or Boot Target #

SysVinit #

SysVinit uses the /etc/inittab file to set the default runlevel.

1. Open /etc/inittab for editing:

   sudo nano /etc/inittab
   

2. Set the default runlevel:
   Look for the line that starts with id: and set the desired runlevel. For example, to set the default runlevel to 3:

   id:3:initdefault:
   

Systemd #

Systemd uses targets instead of runlevels. The default target is typically a symbolic link to a target file.

1. View the current default target:

   systemctl get-default
   

2. Set the default target:

   sudo systemctl set-default multi-user.target
   

2. Changing Runlevels/Boot Targets #

SysVinit #

1. Change to a different runlevel:
   Use the init or telinit command followed by the runlevel number. For example, to switch to runlevel 1 (single-user mode):

   sudo init 1
   

Systemd #

1. Change to a different target:
   Use the systemctl isolate command followed by the target name. For example, to switch to rescue mode (single-user mode):

   sudo systemctl isolate rescue.target
   

3. Shutting Down and Rebooting #

SysVinit #

1. Shutdown the system:

   sudo shutdown -h now
   

2. Reboot the system:

   sudo shutdown -r now
   

Systemd #

1. Shutdown the system:

   sudo systemctl poweroff
   

2. Reboot the system:

   sudo systemctl reboot
   

4. Alerting Users Before Switching Runlevels/Boot Targets #

1. Send a message to all logged-in users using wall:

   sudo wall "System will switch to single-user mode in 5 minutes. Please save your work."
   

5. Properly Terminating Processes #

SysVinit #

1. Gracefully terminate processes before changing runlevels:
   This is typically handled by the scripts in /etc/init.d/. For example, stopping the Apache service:

   sudo /etc/init.d/apache2 stop
   

Systemd #

1. Stop a service before changing targets:
   Use systemctl stop followed by the service name. For example, stopping the Apache service:

   sudo systemctl stop apache2
   

6. Awareness of acpid #

acpid (Advanced Configuration and Power Interface Daemon) handles power-related events, such as closing a laptop lid or pressing a power button.

1. Check if acpid is installed and running:

   systemctl status acpid
   

2. Install acpid if necessary:

   sudo apt-get install acpid
   

3. Start acpid:

   sudo systemctl start acpid
   

Key Files, Terms, and Utilities #

• /etc/inittab: Configuration file for SysVinit to set default runlevel.
• shutdown: Command to shutdown or reboot the system.
• init and telinit: Commands to change runlevels in SysVinit.
• /etc/init.d/: Directory containing init scripts for SysVinit.
• systemd and systemctl: Tools for managing systemd services and targets.
• /etc/systemd/ and /usr/lib/systemd/: Directories containing systemd configuration and service files.
• wall: Command to send messages to all logged-in users.

By mastering these concepts and commands, you’ll be well-prepared to manage runlevels and boot targets effectively, a crucial skill for passing the LPIC-1 exam.