why do we use systemd?

[Glenn Holmer]

On 07/05/2014 06:21 PM, Tim wrote:
> Allegedly, on or about 05 July 2014, Patrick O'Callaghan sent:
>> More to the point, to understand "target" I now have to understand
>> "unit". According to systemd(1), under the heading "Concepts", we find
>> that "systemd provides a dependency system between various entities
>> called "units" of 12 different types". 12 different types! I'm getting
>> a sinking feeling already ... 
> 
> The old system was considered bad, because it had 6 run levels, of which
> a few of them were never used.  Now we have 12?

Twelve different types of *units*, of which service and target are two.
A target is like a runlevel (it groups units together), except that more
than one can be active at a time. A target can be marked
"AllowIsolate=yes", which means that it can be treated like a sysvinit
runlevel (start everything listed in it and stop everything else).

Note also that backward-compatible symlinks are provided in
/usr/lib/systemd/system for the targets that correspond to the
"classical" sysvinit runlevels:

runlevel0.target -> poweroff.target
runlevel1.target -> rescue.target
runlevel2.target -> multi-user.target
runlevel3.target -> multi-user.target
runlevel4.target -> multi-user.target
runlevel5.target -> graphical.target
runlevel6.target -> reboot.target

https://fedoraproject.org/wiki/Systemd#How_do_I_change_the_target_.28runlevel.29_.3F

https://fedoraproject.org/wiki/SysVinit_to_Systemd_Cheatsheet

-- 
Glenn Holmer (Linux registered user #16682)
"After the vintage season came the aftermath -- and Cenbe."