How to rebuild Master & MSDB database

Rebuilding MSDB database if its corrupted and dont have backup

Rebuilding MSDB can be achieved by using Instmsdb script which eliminate all the details stored  in MSDB for alerts, job, Maintainence plan, backup history,Policy based management settings, database mail, performance data warehouse etc.  
1. Stop the SQL Server Instance, SQL Agent, SSRS, SSIS and all other instance related to data store. 
2. In the CMD start the sql instance with below cmd 
NET START MSSQLSERVER /T3608
Trace flag 3608 prevents SQL Server from automatically starting and recovering any database except the master database.

3. In another CMD line detach the MSDB db 

SQLCMD -E -S <SERVERNAME> -dmaster -Q "Exec sp_detach_db msdb"

4. In the SQL data folder rename the existing msdb files to different name.

5. Using SQL Configuration manager start the SQL instance normally.

6.  In the CMD connect to sql server and exec the command 

SQLCMD -E<SERVERNAME> -i"C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\Install\instmsdb.sql" -o"C:\Program Files\Microsoft SQL Server\MSSQL12.MSSQLSERVER\MSSQL\Install\instmsdb.out"

7. Check any errors logged in instmsdb file

8. Reapply if any service packs or hot fixes.

9. Recreate the jobs ,alerts  etc

10. Backup the msdb db. 

REBUILDING THE MASTER DATABASE

Prerequisites

1. Record all the server wide configuration values

select * from sys.configurations

2. Record all service packs and hotfixes applied to the instance of SQL Server and the current collation. You must reapply these updates 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\MSSQL12.MSSQLSERVER\MSSQL\Binn\Templates. 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.

To rebuild system databases for an instance of SQL Server:

1. Insert the SQL Server 2014 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. The default location on the server is C:\Program Files\Microsoft SQL Server\120\Setup Bootstrap\Release.

2. From a command prompt window, enter the following command. Square brackets are used to indicate optional parameters. Do not 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]