fcntl(2)

Return a new file descriptor having the following characteristics:

Get the close-on-exec flag associated with the file descriptor fildes. If the low-order bit is 0 the file will remain open across exec(2), otherwise the file will be closed upon execution of exec(2).

Set the close-on-exec flag associated with fildes to the low-order bit of the third argument, arg, taken as an integer of type int (see F_GETFD).

Get file status flags and access modes; see fcntl(5).

Set file status flags to the third argument, arg, taken as an integer of type int. Only certain flags can be set; see fcntl(5). It is not possible to set both O_NDELAY and O_NONBLOCK.

Get the first lock that blocks the lock described by the variable of type struct flock pointed to by the third argument, arg, taken as a pointer to type struct flock. The information retrieved overwrites the information passed to fcntl() in the flock structure. If no lock is found that would prevent this lock from being created, the structure is passed back unchanged, except that the lock type is set to F_UNLCK.

Set or clear a file segment lock according to the variable of type struct flock pointed to by the third argument, arg, taken as a pointer to type struct flock (see fcntl(5)). The cmd F_SETLK is used to establish read (F_RDLCK) and write (F_WRLCK) locks, as well as to remove either type of lock (F_UNLCK). If a read or write lock cannot be set, fcntl() returns immediately with an error value of -1.

This cmd is the same as F_SETLK except that if a read or write lock is blocked by other locks, the process will sleep until the segment is free to be locked.

If fildes refers to a socket, fcntl() returns the process or process group ID specified to receive SIGURG signals when out-of-band data is available. Positive values indicate a process ID; negative values, other than -1, indicate a process group ID.

If fildes refers to a socket, fcntl() sets the process or process group ID specified to receive SIGURG signals when out-of-band data is available, using the value of the third argument, arg, taken as type int. Positive values indicate a process ID; negative values, other than -1, indicate a process group ID.

Same as F_GETLK, except arg is a pointer to struct flock64 instead of struct flock.

Same as F_SETLK, except arg is a pointer to struct flock64 instead of struct flock.

Same as F_SETLKW, except arg is a pointer to struct flock64 instead of struct flock.

A read lock prevents any other process from write-locking the protected area. More than one read lock can exist for a given segment of a file at a given time. The file descriptor on which a read lock is being placed must have been opened with read access.

A write lock prevents any other process from read-locking or write-locking the protected area. Only one write lock may exist for a given segment of a file at a given time. The file descriptor on which a write lock is being placed must have been opened with write access.

The structure flock describes the type (l_type), starting offset (l_whence), relative offset (l_start), size (l_len), and process ID (l_pid) of the segment of the file to be affected. The process ID field is only used with the F_GETLK cmd to return the value of a block in lock. Locks can start and extend beyond the current end of a file, but cannot be negative relative to the beginning of the file. A lock can be set to always extend to the end of file by setting l_len to zero (0). If such a lock also has l_start set to zero (0), the whole file will be locked. Changing or unlocking a segment from the middle of a larger locked segment leaves two smaller segments for either end. Locking a segment already locked by the calling process causes the old lock type to be removed and the new lock type to take effect. All locks associated with a file for a given process are removed when a file descriptor for that file is closed by that process or the process holding that file descriptor terminates. Locks are not inherited by a child process in a fork(2) system call.

When enforcement-mode file and record locking is activated on a file (see chmod(2)), future read() and write() system calls on the file are affected by the record locks in effect.

A new file descriptor.

Value of close-on-exec flag (only the low-order bit is defined).

Value other than -1.

Value of file status flags and access modes.

Value other than -1.

Value other than -1.

Value other than -1.

Value other than -1.

Value of process or process group ID specified to receive SIGURG signals when out-of-band data is available.

Value other than -1.

Value other than -1.

Value other than -1.

Value other than -1.

fildes is not a valid open file descriptor, or was not opened for reading when setting a read lock or for writing when setting a write lock.

cmd is F_DUPFD and the maximum number of file descriptors is currently open.

cmd is F_SETLK or F_SETLKW, the type of lock is a read or write lock, and no more file-locking headers are available (too many files have segments locked).

cmd is F_DUPFD and arg is greater than or equal to the maximum number of file descriptors.

cmd is F_DUPFD and arg is negative.

cmd is F_GETLK, F_SETLK, or F_SETLKW, and arg or the data it points to is not valid, or fildes refers to a file that does not support locking.

cmd is not a valid command.

cmd is F_SETFL and both O_NONBLOCK and O_NDELAY are specified.

cmd is F_SETLKW and the call was interrupted by a signal.

cmd is F_SETLK, the type of lock (l_type) is a read lock (F_RDLCK) or write lock (F_WRLCK) and the segment of a file to be locked is already write-locked by another process, or the type is a write lock (F_WRLCK) and the segment of a file to be locked is already read- or write-locked by another process.

cmd is F_SETLK or F_SETLKW, the type of lock is a read or write lock, and no more file-locking headers are available (too many files have segments locked), or no more record locks are available (too many file segments locked).

cmd is F_SETLK or F_SETLKW, the type of lock (l_type) is a read lock (F_RDLCK) or write lock (F_WRLCK) and the file is an NFS file with access bits set for enforcement mode.

cmd is F_GETLK, F_SETLK, or F_SETLKW, the file is an NFS file, and a system error occurred on the remote node.

cmd is F_GETLK and the blocking lock's starting offset or length would not fit in the caller's structure.

cmd is F_SETLKW, when the lock is blocked by a lock from another process and sleeping (waiting) for that lock to become free. This causes a deadlock situation.

cmd is F_SETLK or F_SETLKW, and the file is mapped in to virtual memory via the mmap() system call (see mmap(2)).

cmd is either F_GETLK, F_SETLK, or F_SETLKW, and arg points to an illegal address.

cmd is F_GETOWN or F_SETOWN, and fildes does not refer to a socket.