There is nothing really Linux-specific in that, except the default value for some paths like
FG_HOME depends on the OS.
The most important thing is
FG_ROOT. You must, one way or another, tell FG where you have FGData (or the
base package, which AFAIK is the contents of the FGData Git repository, without history information, but with a few more things suitable for a default installation such as a small scenery chunk around the default airport, for people who just installed FG and want to start flying without downloading anything). If you use a launcher, there is certainly a setting to tell FG the corresponding path; otherwise, you can use --fg-root=/path/to/FGData, or set the FG_ROOT environment variable. If you compile FG yourself, it can remember a value passed at compile-time so that you don't have to pass --fg-root, unless you want to use another location. But there are other ways to avoid tedious typing of the same options: launchers, $FG_HOME/fgfsrc, and home-made scripts.
FG_HOME doesn't have to be set. In fact, it is discouraged unless you really need to change it. Just rely on the platform default for your OS. On Linux, it is $HOME/.fgfs.
With both of these, FG can run. But generally, you also want aircraft and scenery. There are always a few default aircraft in FGData (c172p and ufo + variants). If you want more, you have to install them. How to do so and tell FG where they are depends on how you start FG, so we would need to know that. Basically, there are two ways:
- With the built-in launcher (fgfs --launcher), there is a sort of package manager for aircraft, allowing to install and update aircraft by clicking on obvious buttons.
- With and without the built-in launcher, you can also use aircraft downloaded from FGAddon. fgfs supports a --fg-aircraft option (that can be passed several times) that you can use to tell him where you have additional aircraft (i.e., the ones in places different from $FG_ROOT/Aircraft). There is also an FG_AIRCRAFT environment variable that does the same thing, and often we use the $FG_AIRCRAFT notation to informally represent your setting, regardless of how you've specified it (be it with --fg-aircraft or with the environment variable).
Finally, there is scenery. At a high-level, the situation is similar to aircraft: FG looks for scenery in folders specified with --fg-scenery options, in the TerraSync directory as well as in $FG_ROOT/Scenery (collectively and slightly informally referred to as
$FG_SCENERY). Contrary to aircraft, there is no default scenery in FGData, because updating it regularly would make FGData absolutely huge since it is a Git repository. So, unless you get scenery from the
base package(*), or from TerraSync, or install some manually, you get to start in water (frequent question here...).
When you download aircraft from the built-in launcher, or scenery from TerraSync (the wiki page is outdated, it is integrated in FG nowadays and already based on HTTP), the data goes inside the
download directory. On Linux, this is by default
$FG_HOME, i.e. (still on Linux) $HOME/.fgfs. You may choose a different one with --download-dir. There is also --terrasync-dir to specifically choose the TerraSync dir, but --download-dir is more useful in general. If you divert from the default values, you need to reflect it on --fg-aircraft and --fg-scenery, otherwise FG won't find what you've downloaded (or use equivalent GUI settings in a launcher, since I don't know how you start FG...).
There is no standard place where to install additional aircraft or scenery. Just use the options mentioned above so that FG can find them. For --fg-aircraft and --fg-scenery, two syntaxes are possible:
- --fg-foobar=/path1 --fg-foobar=/path2 ...
- --fg-foobar=/path1:/path2:...:/last_path
(I think you can mix both, but that's weird.
foobar stands for aircraft or scenery, of course; on Windows, the path separator is a semicolon instead of a colon)
If you want more help, tell us how you start FG and please try to be more specific...
(*) In which case it is in $FG_ROOT/Scenery... once you've set up FG_ROOT properly, that is.