James Tyrer wrote:
> Duncan wrote:
>
>> James Tyrer posted on Thu, 07 Jan 2010 11:11:15 -0700 as excerpted:
>>
>>
>>> Duncan wrote:
>>>
>>>> James Tyrer posted on Wed, 06 Jan 2010 16:07:26 -0700 as
>>>> excerpted:
>>>>
>>>>
>>>>> However, these instructions are wrong:
>>>>>
>>>>> http://cblfs.cross-lfs.org/index.php/Starting_KDE
>>>>>
>>>>> I suggest that you try this for your ~/.xinitrc file:
>>>>>
>>>>> ------8<------8<------8<------8<------8<------8<------8<------8<------
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> eval `dbus-launch --sh-syntax --exit-with-session`
>>>>>
>>>>> exec startkde
>>>>>
>>>>> ------8<------8<------8<------8<------8<------8<------8<------8<------
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>> According to the dbus-launch manpage I have here, the
>>>> instructions at the given URL (the starting dbus ones) appear to
>>>> do about the same thing, except that dbus instance should start
>>>> and stop with the session, which is what's desired if you're
>>>> doing it that way. Why are they wrong?
>>>>
>>>> Here's the (single) line they use (minus the echo to the
>>>> ~/.xinitrc bit), reprinted here for comparison:
>>>>
>>>> exec dbus-launch --exit-with-session startkde
>>>>
>>>>
>>> First, there is an error is in this line:
>>>
>>> echo "exec dbus-launch --exit-with-session startkde" >> ~/.xinitrc
>>>
>>> Note the ">>", that is wrong.
>>>
>> Why is that wrong? It's the file-redirect and append (instead of
>> replacing). Thus, it appends that line to the end of .xinitrc if it
>> exists already, and creates it with that line, if not.
>>
>
> You should use one or the other of the commands to replace "~/.xinitrc",
> not both: "use the following command instead of the one shown above".
>
> If you append:
>
> exec dbus-launch --exit-with-session startkde
>
> to "~/.xinitrc" and there is an "exec" command before it, control will
> never reach that line.
>
>
>> Presumably, the user may have several other things already setup to
>> run when starting X, and would not want them to be overwritten.
>>
>
> Absolutely correct and that is why you should edit the file rather than
> just using the "echo" command. However, if there is an "exec" command,
> that would need to be removed.
>
>
>> Also, because it's an exec, the new command runs in the existing
>> process, replacing the bash code running the script with the
>> dbus-launch program, so you wouldn't want it anywhere else /but/ the
>> end of an existing .xinitrc, since it's not conditional, and if it
>> were any place but the bottom, the rest of the script wouldn't get
>> run. So, appending to the existing file (if it exists) would seem to
>> be exactly the intended effect.
>>
>
> But, not if there is already an "exec" command.
>
> What I think is likely is that people will not read the page and will
> execute both:
>
> echo "exec startkde" > ~/.xinitrc
>
> echo "exec dbus-launch --exit-with-session startkde" >> ~/.xinitrc
>
> and it obviously will not start D-Bus.
>
> IAC, they should both just have either ">" or ">>", there is no reason
> for one to have one and one the other.
>
>
>> (They do mention to be sure there's no other WMs started above it,
>> however, which would again be desired, and confirms the intent to
>> have what's there remain and continue to function, just now, with the
>> new line invoking dbus to startkde.)
>>
>>
> And that is why you should edit the file rather than use the "echo" lines.
>
>
>>> I have to say that I do not know exactly why the D-Bus
>>> documentation said to do this:
>>>
>>> eval `dbus-launch --sh-syntax --exit-with-session`
>>>
>>> as you probably know, using "eval" make the command take effect in
>>> the current Bash session. Which appears to be what you want.
>>>
>> Well, there's basically two ways to accomplish the same thing --
>> arranging for the dbus-launcher to track the session that's doing the
>> startx. Using the eval method, it runs it in the same session, but
>> the launcher then forks off the daemon (after getting the info about
>> the session that it needs so it can track it) and returns control to
>> the script, while printing the necessary dbus info for the WM (using
>> --sh- syntax) to STDOUT. The eval then takes are of setting up the
>> environment from that output, such that an exec of the WM launcher
>> (startkde in our case) further down the script will have the
>> information about the dbus instance that the wm launcher needs all
>> setup. The two sides thus know about each other, and the dbus daemon
>> can track the wm session and shut down when it does. This method
>> does the dbus launch first, then later, the wm launch-exec, on a
>> different line.
>>
>> The other way to do it is as that kde page mentions, all in one line.
>> When a program is supplied to dbus-launcher as a parameter (it's the
>> only non-option argument, with everything following being args for
>> the invoked program), dbus-launcher itself launches it (as well as
>> dbus), setting the environment appropriately before doing so. As
>> such, the dbus-launcher invoking script no longer needs to know the
>> information otherwise handed to it on STDOUT, so in that case, STDOUT
>> doesn't get it. Since dbus- launcher takes care of setting up the
>> WM-launcher in this case, the two are accomplished all on the same
>> line, with no second line needed (which is of course the reason for
>> the exec in that case, it's slightly more efficient reusing the same
>> process instead of setting up a new one, and that makes sure any
>> other environment settings, etc, carry over, even if they're not
>> exported).
>>
>> So, unless I've seriously missed something, I don't see what's wrong
>> with either method. They're just two different ways of doing the
>> same thing, one running dbus-launch first, as a separate command,
>> then the WM- launcher, the second handing the WM-launcher to
>> dbus-launch as a parameter, so it's all accomplished in a single
>> line.
>>
>> That's why I'm asking what's wrong. Because I can't figure it out,
>> but I've been known to overlook the obvious on occasion, and in fact
>> am still learning "neat bash tricks" (and unfortunate bash
>> misunderstandings) myself, so I'm just wondering if this is a "neat
>> dbus-launcher trick" (and/or a bash redirect trick) you didn't
>> understand, or an "unfortunate bash misunderstanding" of my own.
>> Either way, I'm learning stuff, and expect you might be doing so as
>> well.
>>
>>
> I think that the question is whether:
>
> eval `dbus-launch --sh-syntax --exit-with-session`
>
> exec startkde
>
> and
>
> dbus-launch --sh-syntax --exit-with-session
>
> exec startkde
>
> will have the same effect. IIUC, they will not.
>
>
I was using as follows:
cat .xinitrc
# Begin .xinitrc file
eval `dbus-launch --sh-syntax --exit-with-session`
exec startkde 2>&1 | tee ~/.xsession-errors
Regards
Sagara
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