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

[Chad]

Mr. Chevalier,
Thank you for your time and reply.

On 6/23/2015 1:30 PM, Ronny Chevalier wrote:
> 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 :)
Great, thanks.
>> 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.
I use bash. This is a cool trick that systemd has over init.d. I know not all programs can do that shell completion, for 
example /etc/init.d/httpd res<tab> does not work (I try it all the time out of tab completion habit!).
>
>>
>> #####
>> 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
Ok, so that is a lot more to remember than ls -l /etc/init.d, but I can learn it.
>
>> #####
>> 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
Ok, again more to type and remember, but memorization is not out of the question.
>
>> #####
>> 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.
That is what I am looking for (systemd-sysv-generator), but does that mean systemd will not use the .service files and 
the system will go back to running all start-up scripts in order via init.d style S01-S99?
I don't really care that much as boot time does not matter (I rarely reboot and always have a secondary server that can 
take the load. I run all clusters or active/backup.)
>> 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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