Process Forking and Locks

When a process forks, the child receives a copy of the file descriptors that the parent opened. Locks are not inherited by the child because the locks are owned by a specific process. The parent and child share a common file pointer for each file. Both processes can try to set locks on the same location in the same file. This problem occurs with both lockf() and fcntl(). If a program holding a record lock forks, the child process should close the file. After closing the file, the child process should reopen the file to set a new, separate file pointer. For more information, see the lockf(3C) and fcntl(2) man pages.