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Rebuild system databases

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Applies to: SQL Server

System databases must be rebuilt to fix corruption problems in the master, model, msdb, or resource system databases, or to modify the default server-level collation. This article provides step-by-step instructions to rebuild system databases in SQL Server.

This article is unrelated to rebuilding indexes.

Limitations

When the master, model, msdb, and tempdb system databases are rebuilt, the databases are dropped and recreated in their original location. If a new collation is specified in the rebuild statement, the system databases are created using that collation setting. Any user modifications to these databases are lost. For example, you might have user-defined objects in the master database, scheduled jobs in msdb, or changes to the default database settings in the model database.

Prerequisites

Perform the following tasks before you rebuild the system databases to ensure that you can restore the system databases to their current settings.

  1. Record all server-wide configuration values.

    SELECT * FROM sys.configurations;

  2. Record all hotfixes applied to the instance of SQL Server and the current collation. You must reapply these hotfixes after rebuilding the system databases.

    SELECT
SERVERPROPERTY('ProductVersion ') AS ProductVersion,
SERVERPROPERTY('ProductLevel') AS ProductLevel,
SERVERPROPERTY('ResourceVersion') AS ResourceVersion,
SERVERPROPERTY('ResourceLastUpdateDateTime') AS ResourceLastUpdateDateTime,
SERVERPROPERTY('Collation') AS Collation;

  3. Record the current location of all data and log files for the system databases. Rebuilding the system databases installs all system databases to their original location. If you have moved system database data or log files to a different location, you must move the files again.

    SELECT name, physical_name AS current_file_location
FROM sys.master_files
WHERE database_id IN (DB_ID('master'), DB_ID('model'), DB_ID('msdb'), DB_ID('tempdb'));

  4. Locate the current backup of the master, model, and msdb databases.

  5. If the instance of SQL Server is configured as a replication distributor, locate the current backup of the distribution database.

  6. Ensure you have appropriate permissions to rebuild the system databases. To perform this operation, you must be a member of the sysadmin fixed server role. For more information, see Server-Level Roles.

  7. Verify that copies of the master, model, msdb data and log template files exist on the local server. The default location for the template files is C:\Program Files\Microsoft SQL Server\MSSQL<xx>.MSSQLSERVER\MSSQL\Binn\Templates (where <xx> is the version you have installed). These files are used during the rebuild process and must be present for Setup to succeed. If they are missing, run the Repair feature of Setup, or manually copy the files from your installation media. To locate the files on the installation media, navigate to the appropriate platform directory (x86 or x64) and then navigate to setup\sql_engine_core_inst_msi\Pfiles\SqlServr\MSSQL.X\MSSQL\Binn\Templates.

Rebuild system databases

The following procedure rebuilds the master, model, msdb, and tempdb system databases. You can't specify the system databases to be rebuilt. For clustered instances, this procedure must be performed on the active node and the SQL Server resource in the corresponding cluster application group must be taken offline before performing the procedure.

This procedure doesn't rebuild the resource database. See the section Rebuild the resource system database later in this article.

Rebuild system databases for an instance of SQL Server

  1. Insert the SQL Server installation media into the disk drive, or, from a command prompt, change directories to the location of the setup.exe file on the local server. For SQL Server 2022 (16.x), the default location on the server is C:\Program Files\Microsoft SQL Server\160\Setup Bootstrap\SQLServer2022.

  2. From a command prompt window, enter the following command. Square brackets are used to indicate optional parameters. Don't enter the brackets. When using a Windows operating system that has User Account Control (UAC) enabled, running Setup requires elevated privileges. The command prompt must be run as Administrator.

    setup /QUIET /ACTION=REBUILDDATABASE /INSTANCENAME=InstanceName /SQLSYSADMINACCOUNTS=accounts [ /SAPWD= StrongPassword ] [ /SQLCOLLATION=CollationName ]
    Parameter name Description
    /QUIET or /Q Specifies that Setup should run without any user interface.
    /ACTION=REBUILDDATABASE Specifies that Setup should recreate the system databases.
    /INSTANCENAME=InstanceName The name of the instance of SQL Server. For the default instance, enter MSSQLSERVER.
    /SQLSYSADMINACCOUNTS=accounts Specifies the Windows groups or individual accounts to add to the sysadmin fixed server role. When specifying more than one account, separate the accounts with a blank space. For example, enter BUILTIN\Administrators MyDomain\MyUser. When you are specifying an account that contains a blank space within the account name, enclose the account in double quotation marks. For example, enter NT AUTHORITY\SYSTEM.
    [ /SAPWD=StrongPassword ] Specifies the password for the SQL Server sa account. This parameter is required if the instance uses Mixed Authentication (SQL Server and Windows Authentication) mode.

    Security note: The sa account is a well-known SQL Server account and it is often targeted by malicious users. It is critical that you use a strong password for the sa login.

    Don't specify this parameter for Windows Authentication mode.
    [ /SQLCOLLATION=CollationName ] Specifies a new server-level collation. This parameter is optional. When not specified, the current collation of the server is used.

    Important: Changing the server-level collation doesn't change the collation of existing user databases. All newly created user databases will use the new collation by default.

    For more information, see Set or Change the Server Collation.
    [ /SQLTEMPDBFILECOUNT=NumberOfFiles ] Specifies the number of tempdb data files. This value can be increased up to 8 or the number of cores, whichever is higher.

    Default value: 8 or the number of cores, whichever is lower.
    [ /SQLTEMPDBFILESIZE=FileSizeInMB ] Specifies the initial size of each tempdb data file in MB. Setup allows the size up to 1024 MB.

    Default value: 8
    [ /SQLTEMPDBFILEGROWTH=FileSizeInMB ] Specifies the file growth increment of each tempdb data file in MB. A value of 0 indicates that automatic growth is off and no additional space is allowed. Setup allows the size up to 1024 MB.

    Default value: 64
    [ /SQLTEMPDBLOGFILESIZE=FileSizeInMB ] Specifies the initial size of the tempdb log file in MB. Setup allows the size up to 1024 MB.

    Default value: 8.

    Allowed range: Min = 8, max = 1024.
    [ /SQLTEMPDBLOGFILEGROWTH=FileSizeInMB ] Specifies the file growth increment of the tempdb log file in MB. A value of 0 indicates that automatic growth is off and no additional space is allowed. Setup allows the size up to 1024 MB.

    Default value: 64

    Allowed range: Min = 8, max = 1024.
    [ /SQLTEMPDBDIR=Directories ] Specifies the directories for tempdb data files. When specifying more than one directory, separate the directories with a blank space. If multiple directories are specified the tempdb data files will be spread across the directories in a round-robin fashion.

    Default value: System Data Directory
    [ /SQLTEMPDBLOGDIR=Directory ] Specifies the directory for the tempdb log file.

    Default value: System Data Directory

  3. When Setup has completed rebuilding the system databases, it returns to the command prompt with no messages. Examine the Summary.txt log file to verify that the process completed successfully. This file is located at C:\Program Files\Microsoft SQL Server\160\Setup Bootstrap\Logs.

  4. The RebuildDatabase scenario deletes system databases and installs them again in a clean state. Because the setting of tempdb file count doesn't persist, the value of number of tempdb files isn't known during setup. Therefore, the ebuildDatabase scenario doesn't know the count of tempdb files to be readded. You can provide the value of the number of tempdb files again with the SQLTEMPDBFILECOUNT parameter. If the parameter isn't provided, RebuildDatabase will add a default number of tempdb files, which is as many tempdb files as the CPU count or 8, whichever is lower.

Post-rebuild tasks

After rebuilding the database, you might need to perform the following additional tasks:

  • Restore your most recent full backups of the master, model, and msdb databases. For more information, see Back Up and Restore of System Databases (SQL Server).

    Important

    If you have changed the server collation, do not restore the system databases. Doing so will replace the new collation with the previous collation setting.

    If a backup isn't available or if the restored backup isn't current, re-create any missing entries. For example, re-create all missing entries for your user databases, backup devices, SQL Server logins, end points, and so on. The best way to re-create entries is to run the original scripts that created them.

    Important

    We recommend that you secure your scripts to prevent their being altered by unauthorized by individuals.

  • If the instance of SQL Server is configured as a replication distributor, you must restore the distribution database. For more information, see Back Up and Restore Replicated Databases.

  • Move the system databases to the locations you recorded previously. For more information, see Move System Databases.

  • Verify the server-wide configuration values match the values you recorded previously.

Rebuild the resource database

The following procedure rebuilds the resource system database. When you rebuild the resource database, all hot fixes are lost, and therefore must be reapplied.

Rebuild the resource system database

  1. Launch the SQL Server Setup program (setup.exe) from the distribution media.

  2. In the left navigation area, select Maintenance, and then select Repair.

  3. Setup support rule and file routines run to ensure that your system has prerequisites installed and that the computer passes Setup validation rules. Select OK or Install to continue.

  4. On the Select Instance page, select the instance to repair, and then select Next.

  5. The repair rules will run to validate the operation. To continue, select Next.

  6. From the Ready to Repair page, select Repair. The Complete page indicates that the operation is finished.

Create a new msdb database

If the msdb database is damaged or suspect and you don't have a backup of the msdb database, you can create a new msdb by using the instmsdb script.

Warning

Rebuilding the msdb database using the instmsdb.sql script will eliminate all the information stored in msdb such as jobs, alert, operators, maintenance plans, backup history, Policy-Based Management settings, Database Mail, Performance Data Warehouse, and so on.

  1. Stop all services connecting to the Database Engine, including SQL Server Agent, SSRS, SSIS, and all applications using SQL Server as data store.

  2. Start SQL Server from the command line using the command:

    NET START MSSQLSERVER /T3608

    For more information, see Start, Stop, Pause, Resume, Restart the Database Engine, SQL Server Agent, or SQL Server Browser Service. For information on Trace Flag 3608, see TF3608.

  3. In another command line window, detach the msdb database by executing the following command, replacing <servername> with the instance of SQL Server:

    SQLCMD -E -S<servername> -dmaster -Q"EXEC sp_detach_db msdb"

  4. Using the Windows Explorer, rename the msdb database files. By default these are in the DATA subfolder for the SQL Server instance.

  5. Using SQL Server Configuration Manager, stop and restart the Database Engine service normally with no additional trace flags.

  6. In a command prompt window, connect to SQL Server and execute the command:

    SQLCMD -E -S<servername> -i"C:\Program Files\Microsoft SQL Server\MSSQLXX.INSTANCE_NAME\MSSQL\Install\instmsdb.sql" -o"C:\Program Files\Microsoft SQL Server\MSSQL16.MSSQLSERVER\MSSQL\Install\instmsdb.out"

    Replace <servername> with the instance of the Database Engine. Use the file system path of the instance of SQL Server. Also, replace MSSQLXX.INSTANCE_NAME with the directory that corresponds to your version and instance.

  7. Using the Windows Notepad, open the instmsdb.out file and check the output for any errors.

  8. Reapply any CUs that are installed on the instance, which will upgrade your msdb database to the current CU level.

  9. Recreate the user content stored in the msdb database, such as jobs, alerts, and other items.

  10. Back up the msdb database.

Rebuild the tempdb database

If the tempdb database is damaged or suspect and the database engine fails to start, you can rebuild tempdb without the need to rebuild all system databases.

  1. Rename the current tempdb.mdf and templog.ldf files, if not missing.

  2. Start SQL Server from a Command Prompt by using the sqlservr application.

    sqlservr -c -f -T3608 -T4022 -s <instance> -mSQLCMD

    For a default instance name use MSSQLSERVER, for named instance use MSSQL$<instance_name>. Trace flag 4022 disables execution of startup stored procedures. The -mSQLCMD allows only sqlcmd.exe to connect to the server. For more information, see Other Startup Options.

    Note

    Make sure that the command prompt window remains open after the SQL Server starts. Closing the command prompt window will terminate the process.

  3. Connect to the server by using sqlcmd, and then use the following stored procedure to reset the status of the tempdb database.

    exec master..sp_resetstatus tempdb

  4. Shut down the server by pressing Ctrl+C in the command prompt window.

  5. Restart the SQL Server service. This creates a new set of tempdb database files, and recovers the tempdb database.

Troubleshoot rebuild errors

Syntax and other run-time errors are displayed in the command prompt window. Examine the Setup statement for the following syntax errors:

  • Missing slash mark (/) in front of each parameter name.

  • Missing equal sign (=) between the parameter name and the parameter value.

  • Presence of blank spaces between the parameter name and the equal sign.

  • Presence of commas (,) or other characters that aren't specified in the syntax.

After the rebuild operation is complete, examine the SQL Server logs for any errors. The default log location is C:\Program Files\Microsoft SQL Server\160\Setup Bootstrap\Logs. To locate the log file that contains the results of the rebuild process, change directories to the Logs folder from a command prompt, and then run findstr /s RebuildDatabase summary*.*. This search will point you to any log files that contain the results of rebuilding system databases. Open the log files and examine them for relevant error messages.

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