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);

src/com/sheepit/client/standalone/swing/activity/Settings.java

@@ -51,6 +51,7 @@ import com.sheepit.client.hardware.cpu.CPU;
 import com.sheepit.client.hardware.gpu.GPU;
 import com.sheepit.client.hardware.gpu.GPUDevice;
 import com.sheepit.client.network.Proxy;
+import com.sheepit.client.os.OS;
 import com.sheepit.client.standalone.GuiSwing;
 
 public class Settings implements Activity {
@@ -240,13 +241,15 @@ public class Settings implements Activity {
 		}
 		
 		// priority
-		priority = new JSlider(-19, 19);
-		priority.setMajorTickSpacing(5);
+		OS os = OS.getOS();
+		boolean high_priority_support = os.getSupportHighPriority();
+		priority = new JSlider(high_priority_support ? -19 : 0, 19);
+		priority.setMajorTickSpacing(19);
 		priority.setMinorTickSpacing(1);
 		priority.setPaintTicks(true);
 		priority.setPaintLabels(true);
 		priority.setValue(config.getPriority());
-		JLabel priorityLabel = new JLabel("Priority (High <-> Low):");
+		JLabel priorityLabel = new JLabel(high_priority_support ? "Priority (High <-> Low):" : "Priority (Normal <-> Low):" );
 		
 		compute_devices_constraints.weightx = 1.0 / gpus.size();
 		compute_devices_constraints.gridx = 0;