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master Database
The master database records all the system-level information for
a SQL Server system. This includesinstance-wide metadata such as
logon accounts, endpoints, linked servers, and system
configurationsettings. In SQL Server, system objects are no longer
stored in the master database; instead, they arestored in the
Resource database . Also, master is the database that records the
existence of all otherdatabases and the location of those database
files and records the initialization information for SQLServer.
Therefore, SQL Server cannot start if the master database is
unavailable.Physical Properties of masterThe following table lists
the initial configuration values of the master data and log files.
The sizes of thesefiles may vary slightly for different editions of
SQL Server.
File Logical name Physical name File growth
Primary data master master.mdf Autogrow by 10 percent until the
disk is full.
Log mastlog mastlog.ldf Autogrow by 10 percent to a maximum of 2
terab
For information about how to move the master data and log files,
see Move System Databases . The Resource database depends on the
location of the master database. If you movethe master database,
you must also move the Resource database to the same
location.Database OptionsThe following table lists the default
value for each database option in the master database and
whetherthe option can be modified. To view the current settings for
these options, use the sys.databases catalogview.
Database option Default value Can b
ALLOW_SNAPSHOT_ISOLATION ON No
ANSI_NULL_DEFAULT OFF Yes
ANSI_NULLS OFF Ye
ANSI_PADDING OFF Ye
ANSI_WARNINGS OFF Ye
ARITHABORT OFF Ye
AUTO_CLOSE OFF No
AUTO_CREATE_STATISTICS ON Yes
AUTO_SHRINK OFF No
AUTO_UPDATE_STATISTICS ON Yes
AUTO_UPDATE_STATISTICS_ASYNC OFF Yes
CHANGE_TRACKING OFF No
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CONCAT_NULL_YIELDS_NULL OFF Yes
CURSOR_CLOSE_ON_COMMIT OFF Yes
CURSOR_DEFAULT GLOBAL Yes
Database Availability Options ONLINEMULTI_USERREAD_WRITE
DATE_CORRELATION_OPTIMIZATION OFF Yes
DB_CHAINING ON No
ENCRYPTION OFF No
NUMERIC_ROUNDABORT OFF Yes
PAGE_VERIFY CHECKSUM Yes
PARAMETERIZATION SIMPLE Yes
QUOTED_IDENTIFIER OFF Yes
READ_COMMITTED_SNAPSHOT OFF No
RECOVERY SIMPLE Ye
RECURSIVE_TRIGGERS OFF Yes
Service Broker Options DISABLE_BROKER No
TRUSTWORTHY OFF Ye
For a description of these database options, see ALTER DATABASE
(Transact-SQL). RestrictionsThe following operations cannot be
performed on the master database:
Adding files or filegroups. Changing collation. The default
collation is the server collation. Changing the database owner.
master is owned by sa . Creating a full-text catalog or full-text
index. Creating triggers on system tables in the database. Dropping
the database. Dropping the guest user from the database. Enabling
change data capture. Participating in database mirroring. Removing
the primary filegroup, primary data file, or log file. Renaming the
database or primary filegroup. Setting the database to OFFLINE.
Setting the database or primary filegroup to READ_ONLY.
Recommendations
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When you work with the master database, consider the following
recommendations: Always have a current backup of the master
database available. Back up the master database as soon as possible
after the following operations:
o Creating, modifying, or dropping any databaseo Changing server
or database configuration valueso Modifying or adding logon
accounts
Do not create user objects in master . If you do, master must be
backed up more frequently. Do not set the TRUSTWORTHY option to ON
for the master database.
What to Do If master Becomes UnusableIf master becomes unusable,
you can return the database to a usable state in either of the
following ways:
Restore master from a current database backup.If you can start
the server instance, you should be able to restore master from a
full databasebackup. For more information, see Restore the master
Database (Transact-SQL) .
Rebuild master completely.If severe damage to master prevents
you from starting SQL Server, you must rebuild master . Formore
information, see Rebuild System Databases .
Restore the master Database (Transact-SQL)
This topic explains how to restore the master database from a
full database backup.
To restore the master database
1. Start the server instance in single-user mode.
For information about how to specify the single-user startup
parameter ( -m ), see Configure Server StartupOptions (SQL Server
Configuration Manager) .
2. To restore a full database backup of master , use the
following RESTORE DATABASE Transact-SQL statement:
RESTORE DATABASE master FROM WITH REPLACE
The REPLACE option instructs SQL Server to restore the specified
database even when a database of thesame name already exists. The
existing database, if any, is deleted. In single-user mode, we
recommendthat you enter the RESTORE DATABASE statement in the
sqlcmd utility . For more information, see Usethe sqlcmd Utility
.
Important
After master is restored, the instance of SQL Server shuts down
and terminates the sqlcmd process. Beforeyou restart the server
instance, remove the single-user startup parameter. For more
information, seeConfigure Server Startup Options (SQL Server
Configuration Manager) .
3. Restart the server instance and continue other recovery steps
such as restoring other databases, attachingdatabases, and
correcting user mismatches.
Example
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The following example restores the master database on the
default server instance. The example assumes that theserver
instance is already running in single-user mode. The example starts
sqlcmd and executes a RESTOREDATABASE statement that restores a
full database backup of master from a disk
device:Z:\SQLServerBackups\master.bak.
Note
For a named instance, the sqlcmd command must specify the -S\
option.C:\> sqlcmd1> RESTORE DATABASE master FROM DISK =
'Z:\SQLServerBackups\master.bak' WITHREPLACE;2> GO
See Also
ReferenceRESTORE (Transact-SQL)
ConceptsComplete Database Restores (Simple Recovery Model)
Complete Database Restores (Full Recovery Model)
Troubleshoot Orphaned Users (SQL Server)
Database Detach and Attach (SQL Server)
Rebuild System Databases
Database Engine Service Startup Options
SQL Server Configuration Manager
Back Up and Restore of System Databases (SQL Server)
Start SQL Server in Single-User Mode
Important
Rebuilding master rebuilds all of the system databases.
Related ContentRebuild System Databases System Databases
sys.databases (Transact-SQL) sys.master_files (Transact-SQL) Move
Database Files
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