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A comprehensive overview of linux system initialization, covering run levels, the systemd init system, and various unit types. It explains the concepts of run levels, their associated daemons, and the role of the /etc/inittab file. The document also delves into the systemd init system, its units, and their types, including services, sockets, devices, mounts, automounts, targets, and snapshots. It further explores the use of the telinit command for system reboot and the systemctl command for managing systemd units. Valuable for understanding the fundamental principles of linux system initialization and its evolution from sysvinit to systemd.
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daemons - answer A background service in the Linux operating system that runs as a process with the letter "d" after it (e.g., httpd, sshd, ftpd) SysVinit - answer An older system initialization method that has been largely superseded by systemd. run level 0 - answer System shutdown Runlevel 1 - answer Single user mode without network and other non-essential capabilities Runlevel 2 - answer Multiuser mode
run level 5 - answer Multiuser mode with GUI Runlevel 6 - answer system reboot /sbin/init - answer program responsible for managing run levels and associated daemons/resources syntax of the /etc/inittab file - answer id:runlevel#action:process The scripts used by init to setup each runlevel are stored in the directory - answer /etc/init.d systemd - answer is the most widely used set of tools to manage system resources and services, which are referred to as units Units - answer consists of a name, a type and a corresponding configuration file. For example, the unit for a httpd server process (like the Apache web server) will be httpd.service on Red Hat based distributions and its configuration file will also be called httpd.service (on Debian based distributions this unit is named apache2.service). name the seven distinct types of systems units - answer 1. Service
Unit type: snapshot - answer a saved state of the system manager (not available on every linux. disto) Upstart initialisation scripts are located - answer /etc/init How could the telinit command be used to reboot the system - answer The command terlinit 6 will alternate to runlevel 6, that is, reboot the system What will happen to the services related to the file /etc/rc1.d/K90network when the system enters runlevel1 - answer Due to the letter K in the beginning of the file name, the related services will be stopped Using command systemctl, how could a user verify if the unit ssd.server is running - answer with command systemctl status ssd.service or systemctl is-active ssd.service In a system based system, what command must be executed to enable activation of the unit ssd.service during system initialisation - answer command: systemctl enable ssd.service executed by root
