What is at issue is that GRASS communicates information among the
various modules thru files. The information about what database a
user is using is contained in the file .grassrc in the user's
home directory. If a user were to run GRASS twice using the same
home address, both session would share the .grassrc file. If the
contents of this file were changed by one session, it would
automatically and instantly be changed for the other. This can
happen if the user logs on to the same machine twice or logs in
for two different machines that have the home directory NFS
mounted and shared. The difference is that GRASS can`t tell if
you do it from 2 machines (it uses process ids to detect
concurrent usage).
However, it IS possible to get GRASS to use a different file
other than $HOME/.grassrc. In fact GRASS decides which file to
use based on the setting of the unix environment variable GISRC.
Of course, the grass4.0 command sets GISRC so if you wanted to
have two sessions each using a different GISRC file you would
need to write your own grass4.0 command and add code to set GISRC
to a unique file name. (One consequence is that grass would
"forget" which database you were using from session to session
unless you implemented a session save/recall database).
But this still isn't quite enough. Even if you managed to allow
the same user to run GRASS with two distinct GISRC files, if both
sessions chose the same database location and mapset, then there
would be trouble. The region and mask are stored in files in the
mapset and changing them in one session would instantly and
automatically change them for the other session.
|
|I put out an email asking about GRASS concurrence and have received
|no response other than one phone call telling me this problem has
|been discussed in the past. I was also told that the problem could
|only be overcome by creating complete multiple copies of GRASS (an
|unsubstantiated rumor?). OK. If that's true, how many files actually
|need to be copied? How many can just be links? If you already have
|one running copy of GRASS on a computer (a 2-3 day process), surely
|creating the second copy can be done using work already accomplished
|on the first. Did anyone ever define this procedure in technical
|detail? If so, please refer me to the proper document or former email
|(I'm new to this exploding list).
|
|Greg Colello
|Carnegie Institution, Department of Plant Biology
|290 Panama St
|Stanford, CA 94305
|ph: 415-325-1521 fax: 415-325-6857
|gcolello@biosphere.stanford.edu
|
|
-----------------------------------------------------------------
Michael Shapiro U.S. Army CERL
email: shapiro@zorro.cecer.army.mil Environmental Division
phone: (217) 352-6511 ext 526 P.O. Box 9005
fax: (217) 373-7222 Champaign, Ill. 61826-9005
-----------------------------------------------------------------