Explicit limitation of master log backups

The product does not allow the master log to be backed up, though you can change to full mode. This change explicitly states no log backup allowed

Author: way0utwest

docs/relational-databases/backup-restore/back-up-and-restore-of-system-databases-sql-server.md

@@ -24,7 +24,7 @@ helpviewer_keywords:
 
 |System database|Description|Are backups required?|Recovery model|Comments|  
 |---------------------|-----------------|---------------------------|--------------------|--------------|  
-|[master](../../relational-databases/databases/master-database.md)|The database that records all of the system level information for a [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] system.|Yes|Simple|Back up **master** as often as necessary to protect the data sufficiently for your business needs. We recommend a regular backup schedule, which you can supplement with an additional backup after a substantial update.|  
+|[master](../../relational-databases/databases/master-database.md)|The database that records all of the system level information for a [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] system.|Yes|Simple|Back up **master** as often as necessary to protect the data sufficiently for your business needs. We recommend a regular backup schedule, which you can supplement with an additional backup after a substantial update. Transaction log backups of master are not supported.|  
 |[model](../../relational-databases/databases/model-database.md)|The template for all databases that are created on the instance of [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)].|Yes|User configurable*|Back up **model** only when necessary for your business needs; for example, immediately after customizing its database options.<br /><br /> **Best practice:** We recommend that you create only full database backups of **model**, as required. Because **model** is small and rarely changes, backing up the log is unnecessary.|  
 |[msdb](../../relational-databases/databases/msdb-database.md)|The database used by [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] Agent for scheduling alerts and jobs, and for recording operators. **msdb** also contains history tables such as the backup and restore history tables.|Yes|Simple (default)|Back up **msdb** whenever it is updated.|  
 |[Resource](../../relational-databases/databases/resource-database.md) (RDB)|A read-only database that contains copies of all system objects that ship with [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)]|No|-|The **Resource** database resides in the mssqlsystemresource.mdf file, which contains only code. Therefore, [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] cannot back up the **Resource** database.<br /><br /> Note: You can perform a file-based or a disk-based backup on the mssqlsystemresource.mdf file by treating the file as if it were a binary (.exe) file, instead of a database file. But you cannot use [!INCLUDE[ssNoVersion](../../includes/ssnoversion-md.md)] restore on the backups. Restoring a backup copy of mssqlsystemresource.mdf can only be done manually, and you must be careful not to overwrite the current **Resource** database with an out-of-date or potentially insecure version.|