When you are using a software as a first time user there are always some problems! For any problems related to a specific GRASS command (you ran r.whatever and it caused error n°78371647....) see GRASS official site or users mailing list (learn to use this precious resource!). In this part of the tutorial you will only find the main problems first time users have using GRASS, expecially if they are not so confident with Unix-like Operative Systems.
This is an advice for Windows users who start using GRASS: remember to close terminals, menus or forms only when the processes you ran have completely finished! If you don't check what's written inside them, you could shut a terminal (or a form) with an active process and this can cause the program not to respond anymore. Don't worry, with a little practice all becomes much easier!
1) Running GRASS you see: "concurrent user not allowed" and GRASS doesn't start...
2) After starting GRASS graphicl interface (tcltkgrass) you can't use the terminal anymore to prompt any command
When GRASS starts, digit tcltkgrass &: only if you write the & the terminal is still available for digiting commands.
3) You've just ran the zoom on a monitor and it remains black, the map(s) is no longer visible...
That's probably because you're running an old version of GRASS (prior to 5.beta10), and you have to re-display MANUALLY the map(s) after running the zoom.
4) Running a command on a monitor you have this error:"monitor x... is in use by user_name" (user_name it's YOUR user name)
The monitor is locked by a previous un-finished operation. Try to:
a) close this operation (press mouse right button on the monitor or on its form);
b) kill the process in this way: first digit ps -a |grep x on the terminal to know the PID, then prompt kill -9 PID ;
c) kill the process as seen before then manually delete locking file by prompting :
5) After running some commands you can't see any output
Many commands can create maps but don't display them automatically: you will have to display it manually using d.rast, d.vect, d.site. Some operations that takes a long while to be concluded run in background, and you will receive an e-mail when they are finished.
6) You are trying to display a file but you can't see anything in the monitor
Be sure that the right region has been set with Region -> Manage region.
7) You can't find some data (and you do know it exists!) anymore
Check if you have set the right location and mapset, and if you have the right permissions to read/write these files/directories.
8) You cannot open some monitors
Check if /GRASSdirectory/locks/computer_name directory can be run/read/wrote by all users (drwxrwxrwx).
9) You are using the zoom and the monitor disappears, then you see this message: "EOF from graphic driver"
The monitor has to be entirely visible when the zoom is running. Restart the monitor and retry.
10) You can't save a 3D view file or more generally you can't remember how to export monitors' image
See d.mon CELL.
11) You were running a command from the menu (for example d.what.rast), then you closed its form and now you can't restart this command or the monitor doesn't respond
To run a command from a form, you have to push the blue Run button. When the command is running this button turns to Stop, when the operation is over Run is again displayed.
Output windows (like d.what.rast output) display Running on the top part of the window when the command is running, and Finished when the operation is over.
To stop a command that interacts with the monitor, ALWAYS remember to stop it by clicking with mouse right button on the monitor or on the Stop button of the form, NEVER close the form (or the terminal) with the X before doing this operation! If you do so you the command or the monitor will not respond.
An example: you've just closed d.what.rast form without stopping the process: if now you try to display something in the monitor you will get an error message saying that the active monitor is already in use by the user "yourself".
Prompt ps -a on the console to have a list of all running processes: each one has a PID (on the first column on the left). Look for d.what.rast PID, then digit kill -9 PID writing PID numbers instead of the letters "PID". Prompt ps -a and you can see that d.what.rast has disappeared from the list, so now the monitor will respond.
If the monitor is still unavailable you have to kill it too. Prompt ps -a |grep x, find the PID, then kill the process as seen before and remove lock files digiting rm /GRASSdirectory/locks/computer_name/*
12) You wrote r.mapcalc formulas but they don't work
Maps name cannot contain algebric symbols (like +/-) or r.mapcalc will see them as common operations. Remember also to check syntax, quotes, spaces, filenames... and try again.
13) You are running a command from the console, entering pippo filename, and GRASS can't find it. But you're sure that the name is pippo
File names are case sensitive, so Pippo, PIPPO, pippo and pippO are four different files! Check file capital letters (you can display a list of available files prompting list on the terminal or using a file manager) and try again.
14) You are trying to import e00 file(s) with m.in.e00 (or SHAPEfiles with v.in.shape) but GRASS cannot find them
Check if they have been copied in the right directory (the one from which you are running GRASS), or write the FULL path in the terminal.
15) You've created some other maps (pippo1, pippo2, pippo3)
by reclassing pippo raster map. You used them many times but today GRASS can't open them
You've probably used g.remove to remove the original pippo map. Reclassed files always need the original map: if you remove it they are useless and cannot be recovered!
16) You want to use maps thet have been created by someone else (ore you created it a long time ago and now you can't remember anything about it!) and you don't understand: file contents, how they have been created, if they have been reclassed or not, if they have been generated by mapcalc and you would like to know which formulas have been used...
In the hist directory of the mapset there's a textfile for each map: inside it you can find file history, including information about reclass and any r.mapcalc operation, or if the original file has been imported from an interchange format. To read these files use a text editor or run r.info.
17) You used the zoom on a map but now you can't restore the previous view
In GRASS what you see on the active monitor is not only the view of the map, but also define the active region, or the part of the map where all the operations take place. So modifying the view with the zoom will also modify current region settings. If there's a region of the map in which you're particularly interested you can save it with g.region options in order to easily load it whenever you want!
For further informations on GRASS installation and many more usage problems see GRASS FAQ on the official site.