How do I truncate a log file in SQL Server?

Shrinking a log file to a specified target size

The following example shrinks the log file in the AdventureWorks database to 1 MB. To allow the DBCC SHRINKFILE command to shrink the file, the file is first truncated by setting the database recovery model to SIMPLE.SQLCopy

USE AdventureWorks2012;  
GO  
-- Truncate the log by changing the database recovery model to SIMPLE.  
ALTER DATABASE AdventureWorks2012  
SET RECOVERY SIMPLE;  
GO  
-- Shrink the truncated log file to 1 MB.  
DBCC SHRINKFILE (AdventureWorks2012_Log, 1);  
GO  
-- Reset the database recovery model.  
ALTER DATABASE AdventureWorks2012  
SET RECOVERY FULL;  
GO