Interpret wiki USE flags

[djwave28]

I have once successfully installed GNOME as a desktop, but after getting more educated on the systemd/openRC am now looking at Openbox .. I am totally new to gentoo and played around some with the emerge and other settings in Gentoo.

When I look at the info on the site for Openbox, i see an intro on USE flags ..

https://wiki.gentoo.org/wiki/Openbox

I get a bit uncertain when I see this. Do I need to add these flags or does the system do that? It is not only here when I get this feeling, so in general it will help me.

I also chose for profile just the desktop version. Do I need to set "-gnome -kde"?

Can somebody bounce me off in the right direction?

Thanks
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[charles17]

To solve your confusion about USE flags you might want to read:

• https://wiki.gentoo.org/wiki/Handbook:Parts/Working/USE
  
• https://wiki.gentoo.org/wiki//etc/portage/package.use

[khayyam]

[djwave28]

[djwave28]

Thanks Khay,

First off I killed my GNOME/systemd and started over. I already run CentOS with GNOME and wanted to try something else.
You give me a perfect example where I start to doubt myself.

[krinn]

Your question seems more "when using useflag globally and when per package"?

Take a simple useflag example: mp3
If you add it globally then any package that use the mp3 useflag will be built with it
and if you add it specifically, then all your packages remain as they are, and the specified package will have mp3 useflag enable.

Why would you get scared to use mp3 globally then?
because some people love to tune their system as small as it could be, no need for mp3 support in vlc if you never play mp3 or any video with mp3 audio in it.

And also because you might not really knows to what "mp3" useflag could be use. While a package might have reading mp3 support always enable, the package may also create mp3 but optionally, instead of building a "mp3save" useflag, the dev might re-use the "mp3" useflag, and so, for this package, mp3 will enable recording mp3, while without it, mp3 reading is always enable.
And if the package use some external libs or package to record mp3, the package will enable deps for that, and all this for a feature you will never use.
Devs try to reuse useflag, but the real meaning for mp3 should be "Add support for reading mp3 files", but in real, you have no guaranty a dev won't use it for something different (in my example, it would not be use to enable reading, but to enable recording). I'm unsure if a real policy exist except a kind of "don't abuse them". But for some people enabling recording of mp3 thru that useflag might be seen as abusing.

But if in your mind: "i care about mp3". enabling mp3 globally should provide mp3 support as much as possible. And a package you didn't even think about will have mp3 enable (let's take a stupid example, mp3 might enable mp3 support on some office app and you didn't knew or think that app could do that).

You can temporary enable/disable a useflag to see its impact on your system: USE="flag -flag" emerge -pvN world
And you can see its impact on a package the same way or check what they "should" do with equery (khayyam mistake the output source, it's not from emerge, but from equery).

While it's also natural to think only about enabling useflag on per package, it's also worth to mention you could also disable them thru it.
You can add mp3 globally (in make.conf so) and -mp3 in package.use for vlc, so mp3 everywhere but not for vlc.

So if you are in doubt, it's better to limit useflag to the application and enable the ones you wish globally without thinking about the application itself but for your system. ie: if you have a need for nls in openbox, your whole system should also have that need, and nls might be better use globally.

[djwave28]

Thank you Krinn,

A somewhat soothing explanation. I understand that i am in control, but for a beginner it is impossible to know all these flags and what they stand for. Moreover what the impact is on the system. Surely the mp3 example is quite clear, but there are lots that I don't have affinity with that require further study.

What risk would be involved if I ignore the USE flags and start tuning afterwards when I slowly master the meaning of these flags? How would I determine if USE flags are "mandatory"?
_________________
Go with the flow like a dead fish!

CPU: i7-2600K
GPU: Radeon HD 6970
Mon: HDTV 1440x900 (Philips 19PFL5422D/27)

[frostschutz]

[Buffoon]

Mandatory USE flags you will not see. Conditionally mandatory USE flags you will see and portage will tell you if there is a conflict.

[khayyam]

[djwave28]

Thanks all ...!!

I am getting a better picture now and look at these flags with less anxiety ...

Thanks for the great help here !!!


Greetz!
_________________
Go with the flow like a dead fish!

CPU: i7-2600K
GPU: Radeon HD 6970
Mon: HDTV 1440x900 (Philips 19PFL5422D/27)