(1) To make a file or other piece of data inaccessible. File locking is a critical component of all multi-user computer systems, including local-area networks. When users share files, the operating system must ensure that two or more users do not attempt to modify the same file simultaneously. It does this by locking the file as soon as the first user opens it. All subsequent users may read the file, but they cannot write to it until the first user is finished.
In addition to file locking, many database management systems support record locking, in which a single record, rather than an entire file, is locked. This enables different users to access different records within the same file without interfering with one another.