On 10/01/2014 11:41 AM, Andreas Mahel wrote:
One more word to units: I've got the impression that you, like some other people on this list, view units like some reimplementation of the service by systemd, which would make systemd a big, monolithic something. However, after looking at some of these units, I see that they are merely configuration files providing the information needed to start,stop, etc. the service. Here you can find the executable that will be run (i. e. /usr/bin/cron), command line parameters, PID file location, etc. This information is used to run a general service control flow, whose logic probably very much resembles what you also find in the init.d scripts (if you compare them, you'll find that most of them are very similar, at least the service control scripts). On top, the unit config file provides dependency information to allow parallel start of independent services.
All in all it's mainly "only" a different way to start/stop the same service executables.
An analogy here is the old favourite Xinetd. It uses similar "unit" files for the services it dispatches and each one has the name of the executable that applies. As for the "only", the real fundamental difference between sysvinit and systemd is simply this: Sysvinit is procedural whereas systemd is declarative[1]. There are many examples of declarative mode constructs in the IT world. Sometimes its termed "table driven'. Sometimes the 'units' are in a database .... that is a SQL-like database :-) I suppose any file system _could_ be called a 'database' :-) Sometimes the tables are individual files as with systemd, sometimes bracketed stanzas as is common with AIX. Sometimes they are single lines in a file. You might compare the 'single line' of the user account in /etc/passwd with the database entry in a LDAP database used by a RAS or RADIUS server. [1] One might conjecture that people brought up solely on proecedural languages might have a systemic shock when faced with declarative ones. Perhaps this sheer alien-ness accounts for the antimpathy by some towards systemd. -- Tortoise: 'How many talking tortoises have you met?' Brutha: 'I don't know.' Tortoise: 'What d'you mean, you don't know?' Brutha: 'Well, they might all talk. They just might not say anything when I'm there.' -- "Small Gods", Terry Pratchett -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org To contact the owner, e-mail: opensuse+owner@opensuse.org