QGIS » QGIS Application

Hi,

this is still present in qgis 1.7.4 and makes qgis crash out & exit(1) on the osgeo live dvd when using one of the sample (multi-user) datasets provided, where the current user does not own the grass location completely. (the location is owned by root and the user owns their mapset within it; for the iso/usb livedvd build all user owned+writable files are held in RAM, which is not practicable for a rich sample geo-dataset)

:-(

thanks,
Hamish

Hi,

some more testing and more ideas.

Micha posted some screenshots of the 1.7.4 error message in the LiveDVD ticket: https://trac.osgeo.org/osgeo/ticket/868

some of what I wrote there, reposted here:

I played around with it a bit more on the LiveDVD ISO. As far as I can tell, to get it to work the user must be the owner of the PERMANENT mapset directory, but not necessarily any files within it. Full write permission is not enough, and AFAICT no files are actually written within the dir during the process (the stat mtime on the directory does not change, which I would expect it would if you created then removed a temporary .gislock file or so within it). Also I noticed with the user owning the PERMANENT/ directory that you could then open read-only maps from other non-owned mapsets (ie nc/landsat/) just fine. perhaps a glibc call to access() is checking for permissions wrongly? (in GRASS access rules the user must actually own the GRASS Mapset directory they open, not just have write permissions there)

QGIS should not be changing the region except if the user explicitly runs the g.region module; it can use the GRASS_REGION environment variable to locally override it without touching the WINDow file on the disk. But since no file seems to be written to PERMANENT I don't think that's the case (and anyway nc_spm_08/user1/ is the open Mapset so if any, that should be the one being modified)

for now a "just make the darn thing work" end user work-around is a slight modification of Micha's earlier suggestion to just change ownership of the PERM dir itself:

sudo chown user /usr/local/share/grass/nc_spm_08/PERMANENT
sudo chown user /usr/local/share/grass/spearfish60/PERMANENT

but as a general solution it is not satisfactory.

regards,
Hamish

ok, so the "MAPSET PERMANENT - permission denied" comes from grass lib/gis/gisinit.c's G__gisinit() when G__mapset_permissions() is run and the current UNIX user does not match the filesystem owner:

    struct stat info;
...
    G_stat(path, &info)
...
    if (info.st_uid != getuid())
        return 0;
    if (info.st_uid != geteuid())
        return 0;

what this indicates is that qgis_master/src/providers/grass/qgsgrass.cpp is running grass/modules/qgis.g.info from QgsGrass::getInfo() with MAPSET=PERMANENT not the one you opened (here "user1").

I notice if I open the GRASS toolbox's GRASS Shell, g.gisenv shows MAPSET=user1 correctly, and "/usr/lib/qgis/grass/modules/qgis.g.info proj" shows the WKT text as expected.

when you open the GRASS mapset this should happen in QgsGrass::setMapset():

   G__setenv( "MAPSET", mapset.toUtf8().data() );

but somehow it is getting replaced by QgsGrass::setLocation()'s

  G__setenv( "MAPSET", "PERMANENT" ); // PERMANENT must always exist

since qgis.g.info.c is a read-only module, a dumb work-around is to change it to use G_no_gisinit() instead of G_gisinit(), but as this may be the cause of other bugs in the grass toolbox the reason it thinks it is in the PERMANENT mapset, when you don't have PERMAMENT open and are not trying to open a map from the PERMANENT mapset (e.g. opening @landsat from @user1) should be investigated.

also, the failure of /usr/lib/qgis/grass/modules/qgis.g.info as called by

  QByteArray data =  QgsGrass::runModule( gisdbase, location, cmd, arguments );

should be caught and safely recovered from instead of crashing the program with a "Floating point exception (core dumped)" as soon as you take another action in the GUI (maybe because the n,s,e,w region was not successfully set or the WKT proj info is uninitialized noise). QgsGrass::runModule() catches the exception and displays the error message, but 'QByteArray data' is not then checked for validity by QgsGrass::getInfo() so it continues on as if everything is ok and it has the info it came wanted.

thanks,
Hamish

Running QGIS 1.7.4 and GRASS 6.4.2 (is that what you mean by "latest"?), I downloaded the uc_basic_spm dataset, and did "chown -R root PERMANENT". THen I could start GRASS, open the user1 LOCATION, and load the data from PERMANENT, with no problems.
I then started QGIS and the GRASS plugin. Opened the same LOCATION/MAPSET nc_basic_spm/user1, and I tried to load one of the layers from PERMANENT, as above. THe error I got is:
Cannot get projection
Cannot run module
command: /usr/local/lib/qgis/grass/modules/qgis.g.info info=proj<br><br>ERROR: MAPSET PERMANENT - permission denied

Just to repeat what Hamish already explained well: This error situation surfaces only in a team or educational environment, when shared data (i.e. in a PERMANENT mapset) needs to be accessible read-only. On the OSGeo Live DVD, permissions on /usr/local/share/grass are correctly set to read-only for the regular system user, specifically to emulate a classroom situation, which works fine for GRASS. But the above error renders the QGIS-GRASS plugin un-usable.

This issue is still present in QGIS 2.6 for Mac OS X downloaded from the KyngChaos page. Using the GRASS plugin I try to access maps in some mapsets (no matter if PERMANENT or another user) and I get a warning popup about the unknow CRS, and the standard qgis "Choose CRS for this layer" window. At this point the file opens if it is a vector, while raster file do not opens and QGIS crashes.

The GRASS location that I attempt to open is on an external HD formatted in NTFS (in case this info could be useful to fix).