Linux Kernel

Question 1

What does the boot loader load into memory?

Answer 1

• both kernel and an initial RAM-based file system (initramfs)
• so that it can be used directly by kernel

Question 2

What does the kernel do once it is loaded into the computers memory?

Answer 2

• initializes and configures the computers memory
• configures all hardware attached to the system
• this includes all processors, I/O subsystems, storage devices, etc
• also loads some necessary user space applications

Question 3

What does the kernel do after setting up hardare and mounting the root filesystem?

Answer 3

• runs /sbin/init
• this becomes the initial process which starts other processes to get the system running
• most other processes trace their origin ultimately to init

Question 4

What processes do not trace their origin ultimately to init?

Answer 4

• kernel processes
• these are started by the kernel directly
• their job is to manage internal OS details

Question 5

For what is init responsible besides starting the system?

Answer 5

• keeping the system running
• shutting processes off cleanly
• act when necessary as a manager of all non-kernel processes
• cleans up after them after completion
• restarts user login / background system services

Question 6

What is systemd?

Answer 6

• established uniform startup process across most distros

Question 7

What are systemd features?

Answer 7

• aggressive parallelization techniques, permitting multiple services to start simultaneously
  Simpler configuration files that enumerate:
• what has to be done before a service is started
• how to execute service startup
• what conditions the service should indicate have been accomplished when startup is finished

Question 8

How does systemd influence the init process?

Answer 8

• /sbin/init now points to /lib/systemd/systemd
• takes over the init process

Question 9

What are example commands of systemd?

Answer 9

Starting, stopping, restarting a service on currently running system:
$ sudo systemctl start|stop|restart httpd.service

Enabling or disabling a system service from starting up at system boot:
$ sudo systemctl enable|disable httpd.service

Checking on the status of a service:
$ sudo systemctl status httpd.service