Chmod Command – How to Use chmod -R 644 on ~/Documents

Using the octal codes has two advantages I can think of, neither of which is that huge:

1. They're shorter, easier to type.
2. A few things only understand them, and if you routinely use them you'll not be scratching your head (or running to documentation) when you run into one. E.g., you have to use octal for chmod in Perl or C.

Sometimes really simple utilities won't handle the "friendly" versions; especially in non-GNU userlands.

Further, some utilities spit out octal. For example, if you run umask to see what your current umask is, it'll spit it out in octal (though in bash, umask -S does symbolic).

So, in short, I'd say the only reason to prefer them is to type fewer characters, but that even if you elect not to use them, you should know how they map so that you can figure out an octal code if you run into one of the things that only does octal. But you don't need to immediately know that 5 maps to rx, you only need to be able to figure that out.

This is a typical behaviour of a filesystem that doesn't understand access permissions - very likely a (V)FAT partition. This is also indicated by the path /media/..., which is where removable media is mounted nowadays.

The permission problem occurring when trying to run the script could be caused by the noexec mount option (which is understandable safeguard for removable media).

If the above is the case (you can verify that in the mount output), you can either run the script by specifying the interpreter, e.g. python /path/to/script, or remount the filesystem with the exec option (which generally is a silly workaround from the security point of view).

As a side note, the first option might not work if you your interpreter will try to use mmap() to load the file into memory and mark it as executable (because the filesystem layer will refuse that). This is usually the case of the dynamic linker ld-linux*.so* (located in lib or /lib64 depending on your system). Python should work though.