I'm new to Linux/Rasperry Pi and I was following this tutorial to create a native build of Qt. I got up to the ./configure step. But this gives me the error:
bash: ./configure Permission denied
I think it has something to do that I want to run the configuration from a USB drive (as instructed in the tutorial). How can I get this to work?
You need to understand how unix modes and permissions, used on POSIX operating systems such as GNU/Linux and OSX work, otherwise your life is going to be full of awkward problems like this. There are already lots and lots of introductions online, I will not bother regurgitating them.
However, I'll give an example of applying the concepts in this case. First, you need to know some id numbers for your current user:
id $(whoami)
Will give you your uid, gid, and a list of groups whose permissions you can use.
./configure is a file. To get the modes and permissions set on it:
stat ./configure
It's in the first line labelled "Access:" (there are two), and will be something like 0755/drwxr-xr-x. All of those links from above explain how to decipher that. See also man stat.
You need to change the ownership on the whole directory tree, since you are going to be building software in it. For that you can use the -R (recursive) switch to chown (see also man chown), but you need privileges to do so, via sudo. Presuming you are in the same directory as the configure file, and you are user pi:
sudo chown -R pi.pi .
You could of course just do sudo ./configure and proceed that way, but this way you are playing safe. On the other hand, if you are intending to do a system wide install, you will need to do so at some point (sudo make install).
Note that this is not necessarily an ownership problem, which will be obvious when you examine the files in question; it can also be purely mode related. To execute a file, it needs to be set as executable (adds 1 to the mode, e.g., 7 is read/write/execute, 6 is read/write, 5 is read/execute, 4 is just read). It would be a bit bizarre in this case, but certainly not impossible depending on how the source archive was unpacked and the USB drive mounted.
sudo ./configure was the first thing I tried. This gives me sudo ./configure: command not found:
stat ./configure tells me I have the permission 0644. Right click on the file say "Execute: Nobody" and I can't seem to change it
sudo, that ./configure has ended up 644, and exactly how the USB stick was mounted (if it was automounted and use a default Raspbian configuration, say, "automounted by LXDE").
.configure might end up non-executable. I don't think they would ship the package that way, and there may be other files with the wrong mode which will cause other problems. Since the instructions included using mount --bind, check and see if the mode/permissions are identical in both places.