[systemd-devel] How to get used to systemd vs init

[Ronny Chevalier]

On Tue, Jun 23, 2015 at 9:45 PM, Chad <ccolumbu at gmail.com> wrote:
> I am sure this is the wrong place to send this e-mail, but I could not find
> another place to send it.

Hi,

It is the good place :)

> I want to learn and use systemd, but have run into a few problems on my way.
> Please don't see this as an attack on systemd, I want to learn something
> new, but change is hard.
>
> I am an old school kind of sysadmin and I am planning on moving from CentOS
> 6 to CentOS 7, but I am having trouble with systemd. I am hoping you know
> some shortcuts/tricks to help me learn the new way.
>
> #####
> 1. I can't spell. With init I don't have to know how to spell things because
> I have tab complete. I use tab complete for almost every command I type. For
> example:
> /e<tab> gets -> /etc/
> /etc/in<tab>  gets -> /etc/init
> /etc/init.<tab>  gets -> /etc/init.d/
> /etc/init.d/ht<tab gets -> /etc/init.d/httpd
> /etc/init.d/httpd restart
> So I entered 19 characters and got 25 with tab complete.
>
> The new systemd way would be to type (23 total characters, no tab complete):
> systemctl restart httpd
> Maybe I could tab complete systemctl, but I don't currently have a CentOS 7
> system to test on.
>
> The real issue is that I have to know (in the above example) that it is
> httpd not http.
> With so many systems, distros, and services it is hard to remember every
> service name exactly (and some names are very long). For example ntpd has a
> d, but nfs does not.
> Tab completion fixes this issue for me.
>
> How can I use tab completion with systemd?

If you use either bash or zsh, systemd provides shell completion for them.

You could do something like:

systemctl start htt<tab>
systemctl st<tab>

or else, and it will complete it.

>
>
> #####
> 2. How to find all possible services:
>
> The init way:
> ls -l /etc/init/d
>
> The systemd way:
> ls -l /lib/systemd/system/*.service /etc/systemd/system/*.service
>
> This seems WAY harder and I have to remember 2 locations instead of 1.

There is:

systemctl list-unit-files

It lists all the units installed on your system. In systemd a unit is
a configuration file that can describe a service, a mount point, a
device,... So a service is a subtype of unit, see "man 5 systemd.unit"
for more information.

So if you want to only display the services, you just have to specify the type

systemctl list-unit-files --type=service

>
> #####
> 3. List all services and their start levels:
>

In systemd world, start levels equivalent are the targets (see man 5
systemd.target). A target is a synchronisation point between multiple
units. For example, there is sysinit.target which is the
synchronization point for early boot services. This way a unit can ask
to be started only after a specific target, for example.

> The init way (all services):
> chkconfig --list
>
> The init way (only active services. I use this a lot):
> chkconfig --list | grep :on
>
> The systemd way (all services):
> systemctl list-unit-files --type=service
>
> The systemd way (only active services, I don't know how to do this).
> systemctl ???
>

With systemctl you can provide a filter according to the current state
of a unit. If you want to list all the active service, you can do:

systemctl --state=active --type=service list-units

>
> #####
> 4. What about the many programs that rely on /etc/init.d/<service>
> status/start/stop/restart
> I have many services that are monitored by nagios or cron jobs (like
> logrotate) that rely on /etc/init.d/<service> status/start/stop/restart.
> I don't want to change them because right now they work on every server and
> I don't want to have to maintain 2 versions of the code or hunt them all
> down.

There is systemd-sysv-generator which creates wrapper .service for
sysv scripts automatically at boot. But you need to specify additional
headers if you want to use ordering. See man systemd-sysv-generator.

> Is there some trick/3rd party script to create /etc/init.d wrappers/scripts
> to make all the services work with the old path?
> Something like:
> ln -s /lib/systemd/system/<service>.service /etc/init.d/<service>
> Or maybe a shell script like:
> service=`basename "$0"`
> systemctl $1 $service
>
> So I would like to move forward with systemd (and will eventually have to if
> I want modern/supported OSs), but systemd seems harder to deal with and will
> break a lot of my existing scripts/cronjobs/monitors.
>
>
> Thank you all for your work on FOSS, you are making the world a better
> place!!
>
> --
>
> ^C
> Chad Columbus
> 20 years of application development and sysadmin
> Currently maintaining about 30 CentOS 6 servers.
> Have maintained over 1,000 linux servers over the years.
>
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