Question

After compiling the following code in Eclipse using a Mac:

    import java.io.*;

    public class Filer{
        public static void main(String[] args) throws IOException{

        File f1;

        f1 = new File("/System/file.txt");

        if(!f1.exists()){
            f1.createNewFile();

        }
      }
    }

I get an error:

    Exception in thread "main" java.io.IOException: Permission denied
        at java.io.UnixFileSystem.createFileExclusively(Native Method)
        at java.io.File.createNewFile(File.java:883)
        at Filer.main(Filer.java:11)

Can anyone tell me why that is? Is there any way to change the permissions? And if I were to compile this as a .jar file and send it to someone, would that person have the correct permissions?

Answer 1

Can anyone tell me why that is?

Your user doesn’t have permission to create a file in that directory.

Is there any way to change the permissions?

The same way you would change the permissions of any directory.

In Java 7+

Files.setPosixFilePermisions(f1.toPath(), 
    EnumSet.of(OWNER_READ, OWNER_WRITE, OWNER_EXECUTE, GROUP_READ, GROUP_EXECUTE));

And if I were to compile this as a .jar file and send it to someone, would that person have the correct permissions?

I suspect the correct permissions for a directory called /System is that you NOT have write access.

Is there any reason not to use the home directory or the current working directory?