Update application file logging error handling (#1776)

* Update application logging configuration instructions
* Update error notification handling when unable to write to required logfile due to access permission issues

docs/USAGE.md

@@ -223,13 +223,26 @@ The requested client activity log will instead be located in the users home dire
 
 On many systems this can be achieved by
 ```text
-mkdir /var/log/onedrive
-chown root.users /var/log/onedrive
-chmod 0775 /var/log/onedrive
+sudo mkdir /var/log/onedrive
+sudo chown root.users /var/log/onedrive
+sudo chmod 0775 /var/log/onedrive
 ```
 
 All log files will be in the format of `%username%.onedrive.log`, where `%username%` represents the user who ran the client.
 
+Additionally, you need to ensure that your user account is part of the 'users' group:
+```
+cat /etc/group | grep users
+```
+
+If your user is not part of this group, then you need to add your user to this group:
+```
+sudo usermod -a -G users <your-user-name>
+```
+
+You then need to 'logout' of all sessions / SSH sessions to login again to have the new group access applied.
+
+
 **Note:**
 To use a different log directory rather than the default above, add the following as a configuration option to `~/.config/onedrive/config`:
 ```text

src/log.d

@@ -13,6 +13,7 @@ version(Notifications) {
 // enable verbose logging
 long verbose;
 bool writeLogFile = false;
+bool logFileWriteFailFlag = false;
 
 private bool doNotifications;
 
@@ -35,7 +36,7 @@ void init(string logDir)
 			// we got an error ..
 			writeln("\nUnable to access ", logFilePath);
 			writeln("Please manually create '",logFilePath, "' and set appropriate permissions to allow write access");
-			writeln("The requested client activity log will instead be located in the users home directory\n");
+			writeln("The requested client activity log will instead be located in your users home directory\n");
 		}
 	}
 }
@@ -169,6 +170,17 @@ private void logfileWriteLine(T...)(T args)
 		// We cannot open the log file in logFilePath location for writing
 		// The user is not part of the standard 'users' group (GID 100)
 		// Change logfile to ~/onedrive.log putting the log file in the users home directory
+		
+		if (!logFileWriteFailFlag) {
+			// write out error message that we cant log to the requested file
+			writeln("\nUnable to write activity log to ", logFileName);
+			writeln("Please set appropriate permissions to allow write access to the logging directory for your user account");
+			writeln("The requested client activity log will instead be located in your users home directory\n");
+		
+			// set the flag so we dont keep printing this error message
+			logFileWriteFailFlag = true;
+		}
+		
 		string homePath = environment.get("HOME");
 		string logFileNameAlternate = homePath ~ "/onedrive.log";
 		logFile = File(logFileNameAlternate, "a");