On linux, only the root can create process with high priority, so don't display the option is the client is launched as regular user

src/com/sheepit/client/os/Linux.java

@@ -167,6 +167,19 @@ public class Linux extends OS {
 		return builder.start();
 	}
 	
+	@Override
+	public boolean getSupportHighPriority() {
+		// only the root user can create process with high (negative nice) value
+		String logname = System.getenv("LOGNAME");
+		String user = System.getenv("USER");
+		
+		if ((logname != null && logname.equals("root"))	|| (user != null && user.equals("root"))) {
+			return true;
+		}
+		
+		return false;
+	}
+	
 	protected void checkNiceAvailability() {
 		ProcessBuilder builder = new ProcessBuilder();
 		builder.command(NICE_BINARY_PATH);

src/com/sheepit/client/os/OS.java

@@ -37,6 +37,10 @@ public abstract class OS {
 		return null;
 	}
 	
+	public boolean getSupportHighPriority() {
+		return true;
+	}
+	
 	public Process exec(List<String> command, Map<String, String> env) throws IOException {
 		ProcessBuilder builder = new ProcessBuilder(command);
 		builder.redirectErrorStream(true);