Most modern Linux distributions are using systemd as the default unit system and service manager. 1
Starting with Ubuntu 18.04 and CentOS 7 SystemD has replaced the old SysVinit script 2
system . However it’s backward compatible with the old SysVinit. 3
In this video will start diving into SystemD. Its name come from System Management Daeman and it 4
is a Linux initialization system and service manager with many components such as on demand service 5
management, logging, boot manager and many more. SystemD is the Linux initialization system 6
during its boot and startup process. 7
The Linux boot process has the following phases: 8
First the system powers up, then the bootloader, which is GRUB loads the kernel, then the kernel loads 9
an initial RAM disk that loads the system dives and looks for the root file system. 10
Once the kernel is set up, it begins the systemd 11
initialization system. systemd starts with PID 1 12
as the first process then takes over and continues to mount the hosts file systems and 13
start services. 14
Let's take a look at the processes that are running ps-ef | less 15
This is systemd. In the process 16
list is displayed as init for backward compatibility. 17
However, this is systemd. 18
So systemd is initializing the system at boot time. 19
Compared to the old init, which started the services sequentially, systemd starts the services 20
in parallel. 21
This is a more efficient and faster way of initializing the system. Let's run systemd- version. 22
This is its version and to show how long the boot process took run systemd analyze. 23
it may be used to determine system boot up performance and statistics. 24
And to print a list of all running units ordered by the time they took to initialize run systemd 25
analyze blame. 26
Good! Systemd introduces the concepts of Systemd units and there are several types, such as a service 27
unit, mount unit, socket unit and slice unit. 28
Units are defined in unit configuration files, which include information about the unit type 29
its behavior. For service management tasks, the unit file contains instructions about how to start, 30
stop or restart the service. 31
The unit has the suffix 32
.service.We will take a short break 33
and in the next lecture, I'll show you how to control systemd and its services. 34
See you in two seconds!