ORA-01157: cannot identify/lock data file

I got ” ORA-01157: cannot identify/lock data file ” error in Oracle.

ORA-01157: cannot identify/lock data file

Details of error are as follows.

ORA-01157: cannot identify/lock data file string - see DBWR trace file

Cause: The background process was either unable to find one of the data files or failed to
 lock it because the file was already in use.

The database will prohibit access to this file but other files will be unaffected.
 However the first instance to open the database will need to access all online data files.
 Accompanying error from the operating system describes why the file could not be identified.

Action: Have operating system make file available to database. Then either open the database
 or do ALTER SYSTEM CHECK DATAFILES.

cannot identify/lock data file

This ORA-01157 errors are related with the background process was either unable to find one of the data files or failed to lock it because the file was already in use.

Mostly if the specified datafile is deleted or corrupt or renamed or moved,  you will get this error.

If the datafile is deleted or corrupt, you need to restore it from backup.

If the datafile is renamed or moved to another location, rename the controlfile using the following post.

How to Move, Rename and Relocate Datafiles in Oracle

Or if the Mount point is incorrect, you will get this error. To solve this error, fix the mount point.
Or if there is  read or write permission on datafile, you will get this error. To solve this error, give the 755 permission or oracle:oinstall ownership.

Do you want to learn Oracle Database for Beginners, then read the following articles.

Oracle Tutorial | Oracle Database Tutorials for Beginners ( Junior Oracle DBA )