Setting up a second monitor

Antony Gelberg antony at
Fri Apr 21 10:22:05 UTC 2006

Jean Hollis Weber wrote:
> Antony Gelberg wrote:
>> Is it a fact that man pages are inappropriate for new users or just 
>> your opinion?  In my opinion they are useful for any level of user, as 
>> are the other types of documentation.  If one wants to understand a 
>> config file, a how-to or tutorial may help a little, but really there 
>> is nothing as focused or accurate as the man page.
> I read the man page for xorg.conf, but it might just as well have been 
> written in Swahili for all the good it did me. Forcused and accurate? 
> I'm sure it is. Informative? Only as a reference for those who already 
> know what it's talking about.
> As for "fact" versus "opinion":
> I have been a technical writer working on user documentation (mainly for 
> a non-technical audience) for over 25 years. If I wanted to take the 
> time, I could cite to you numerous studies showing that man pages and 
> other reference-type documentation is not appropriate for new users, who 
> do not have the background knowledge required to understand the 
> information in them. Not only that, but the vast majority of new users 
> do not want to "understand" a config file or anything else; they just 
> want to know what to do to get the job done. 

These users might want to ponder that there may well be a relationship 
between understanding and getting the job done.  Of course there is a 
balance to be drawn, but one has to understand something about anything 
to make use of it.

> Some of them will 
> eventually want to understand (not just do) and will seek out the 
> information when they are ready for it. Others will not.
> In addition to the studies that back up my opinion, here is another 
> opinion, also based on long experience: My partner Eric has been a Unix 
> hacker for at least 25 years, and he says that man pages are not good 
> for *anyone* to learn from; they are good for reference material for 
> those who already know what the pages are talking about.

I say that if there is a config file or command that I know exists, and 
I don't know what it does or what the syntax is, I run man on it.  I do 
not know what the pages are talking about prior to this, as I do not 
know what the command or file even does, or e.g. what a certain option does.

>> For the OP's task, there is no option but to edit the config file.  If 
>> the how-to is not clear, the man page is a good next port-of-call. 
>> There is no compulsion for the user to read the entire page as he can 
>> just scan it for the relevant sections.
> I don't mind editing a config file; I've done that before.
> Thank you for the pointer to this page:
> It seems to explain things at the right level for me, even though the 
> process does seem complicated. It looks like it will give me the info I 
> need to edit the config file. I hope so!

There is a caveat.  I have mentioned it elsewhere but will do so again. 
  As you'll see from the above link and the Xinerama HOWTO, you need at 
least two Screen stanzas in xorg.conf, each of which includes a unique 
Device and Monitor pair.

Put another way, Device + Monitor = Screen.  man xorg.conf says:
"Each Screen section binds together a graphics board and a monitor.  The 
graphics boards are described in the Device sections, and the monitors 
are described in the Monitor sections."

In the event that your hardware only shows one BusID, which is often the 
case for one video card with dual ports, and it seems that way from your 
replies that I've skimmed, you need to differentiate between the two 
Devices with the Screen parameter, /not/ the BusID.  Differentiating 
between Devices with BusID is more often for two separate video cards in 
one workstation.  NB This analogy doesn't apply well to laptops.

Here is another excerpt from man xorg.conf:
"Screen  number
        This option is mandatory for cards where a single PCI entity can
        drive more than one display (i.e., multiple CRTCs sharing a sin-
        gle  graphics accelerator and video memory).  One Device section
        is required for each head, and this parameter  determines  which
        head  each  of the Device sections applies to.  The legal values
        of number range from 0 to one less  than  the  total  number  of
        heads  per entity.  Most drivers require that the primary screen
        (0) be present."

Based on two examples from the Internet:

For one BusID:

Section "Device"
	Identifier	"Screen0 ATI Technologies Radeon Mobility 7500"
	Driver		"ati"
	BusID		"PCI:1:0:0"
	Option		"DynamicClocks"	"on"
	Screen		0

Section "Device"
	Identifier	"Screen1 ATI Technologies Radeon Mobility 7500"
	Driver		"ati"
	BusID		"PCI:1:0:0"
	Option		"DynamicClocks"	"on"
	Screen		1

For different BusIDs:

Section "Device"
Identifier "nVidia 1"
Driver "nvidia"
BusID "PCI:2:0:0"

Section "Device"
Identifier "nVidia 1"
Driver "nvidia"
BusID "PCI:2:1:0"

More information about the ubuntu-users mailing list