SYS_FLOCK(9) The Linux VFS SYS_FLOCK(9)NAME
sys_flock - flock system call.
long sys_flock(unsigned int fd, unsigned int cmd);
the file descriptor to lock.
the type of lock to apply.
Apply a FL_FLOCK style lock to an open file descriptor. The cmd can be one of
LOCK_SH -- a shared lock.
LOCK_EX -- an exclusive lock.
LOCK_UN -- remove an existing lock.
LOCK_MAND -- a `mandatory' flock. This exists to emulate Windows Share Modes.
LOCK_MAND can be combined with LOCK_READ or LOCK_WRITE to allow other processes read and write access respectively.
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 SYS_FLOCK(9)
Check Out this Related Man Page
FLOCK(2) BSD System Calls Manual FLOCK(2)NAME
flock -- apply or remove an advisory lock on an open file
Standard C Library (libc, -lc)
#define LOCK_SH 1 /* shared lock */
#define LOCK_EX 2 /* exclusive lock */
#define LOCK_NB 4 /* don't block when locking */
#define LOCK_UN 8 /* unlock */
flock(int fd, int operation);
flock() applies or removes an advisory lock on the file associated with the file descriptor fd. A lock is applied by specifying an operation
parameter that is one of LOCK_SH or LOCK_EX with the optional addition of LOCK_NB. To unlock an existing lock operation should be LOCK_UN.
Advisory locks allow cooperating processes to perform consistent operations on files, but do not guarantee consistency (i.e., processes may
still access files without using advisory locks possibly resulting in inconsistencies).
The locking mechanism allows two types of locks: shared locks and exclusive locks. At any time multiple shared locks may be applied to a
file, but at no time are multiple exclusive, or both shared and exclusive, locks allowed simultaneously on a file.
A shared lock may be upgraded to an exclusive lock, and vice versa, simply by specifying the appropriate lock type; this results in the pre-
vious lock being released and the new lock applied (possibly after other processes have gained and released the lock).
Requesting a lock on an object that is already locked normally causes the caller to be blocked until the lock may be acquired. If LOCK_NB is
included in operation, then this will not happen; instead the call will fail and the error EAGAIN will be returned.
Locks are on files, not file descriptors. That is, file descriptors duplicated through dup(2) or fork(2) do not result in multiple instances
of a lock, but rather multiple references to a single lock. If a process holding a lock on a file forks and the child explicitly unlocks the
file, the parent will lose its lock.
Processes blocked awaiting a lock may be awakened by signals.
Zero is returned if the operation was successful; on an error a -1 is returned and an error code is left in the global location errno.
The flock() call fails if:
[EAGAIN] The file is locked and the LOCK_NB option was specified.
[EBADF] The argument fd is an invalid descriptor.
[EINVAL] The argument operation does not include exactly one of LOCK_EX, LOCK_SH, or LOCK_UN.
[EOPNOTSUPP] The argument fd refers to an object other than a file.
SEE ALSO close(2), dup(2), execve(2), fork(2), open(2), flockfile(3), lockf(3)HISTORY
The flock() function call appeared in 4.2BSD.
BSD October 15, 2011 BSD
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