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.\" Copyright 2014 Garrett D'Amore <garrett@damore.org>
.\"
.Dd "Nov 13, 2014"
.Dt FLOCK 3C
.Os
.Sh NAME
.Nm flock
.Nd BSD-compatible file locking
.Sh SYNOPSIS
.In sys/file.h
.
.Ft int
.Fo flock
.Fa "int fd"
.Fa "int operation"
.Fc
.
.Sh DESCRIPTION
The
.Fn flock
function provides a BSD compatibility interface for file locking,
and is implemented in terms of
.Xr fcntl 2 .
.
.Pp
The
.Fa fd
is a file descriptor that references a regular file.  The
.Fa operation
is one of the following.
.Bl -tag -width Dv
.It Dv LOCK_SH
Acquire a shared (non-exclusive) lock.  There may be multiple shared
locks on a file simultaneously.
.It Dv LOCK_EX
Acquire an exclusive lock.
.It Dv LOCK_UN
Release the lock.
.El
.Pp
In addition, the value
.Dv LOCK_NB
can be added to the operation (bitwise-OR) to indicate that the
operation should fail immediately rather than blocking if the
lock cannot be acquired.
.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn flock
function will fail if:
.Bl -tag -width Er
.It Er EBADF
The
.Fa fd
argument is not an open file descriptor.
.
.It Er EINVAL
The
.Fa fd
argument does not reference a regular file, or an invalid
.Fa operation
has been supplied.
.
.It Er EWOULDBLOCK
A lock cannot be immediately acquired due to other conflicting lock(s).
.El
.Sh INTERFACE STABILITY
.Sy Obsolete Committed.
.Sh MT-LEVEL
.Sy MT-Safe .
.Sh SEE ALSO
.Xr fcntl 2 ,
.Xr lockf 3C