www.LinuxHowtos.org

fcntl

Section: System Calls (2)
Updated: 202-0-08
Index Return to Main Contents

NAME

fcntl - manipulate file descriptor

LIBRARY

Standard C library (libc,~-lc)

SYNOPSIS

#include <fcntl.h>
int fcntl(int fd, int op, ...);

DESCRIPTION

fcntl() performs one of the operations described below on the open file descriptor fd. The operation is determined by op. Certain of the operations below are supported only since a particular Linux kernel version. The preferred method of checking whether the host kernel supports a particular operation is to invoke fcntl() with the desired op value and then test whether the call failed with EINVAL, indicating that the kernel does not recognize this value.

Duplicating a file descriptor

F_DUPFD(2const): F_DUPFD_CLOEXEC(2const)

File descriptor flags

F_GETFD(2const): F_SETFD(2const)

File status flags

F_GETFL(2const): F_SETFL(2const)

Advisory record locking

F_SETLK(2const): F_SETLKW(2const) F_GETLK(2const)

Open file description locks (no-POSIX)

F_OFD_SETLK(2const): F_OFD_SETLKW(2const) F_OFD_GETLK(2const)

Managing signals

F_GETOWN(2const): F_SETOWN(2const) F_GETOWN_EX(2const) F_SETOWN_EX(2const) F_GETSIG(2const) F_SETSIG(2const)

Leases

F_SETLEASE(2const): F_GETLEASE(2const)

Delegations

F_SETDELEG(2const): F_GETDELEG(2const)

File and directory change notification (dnotify)

F_NOTIFY(2const)

Changing the capacity of a pipe

F_SETPIPE_SZ(2const): F_GETPIPE_SZ(2const)

File Sealing

F_ADD_SEALS(2const): F_GET_SEALS(2const)

File read/write hints

F_GET_RW_HINT(2const): F_SET_RW_HINT(2const) F_GET_FILE_RW_HINT(2const) F_SET_FILE_RW_HINT(2const)

RETURN VALUE

For a successful call, the return value depends on the operation. On error, -1 is returned, and errno is set to indicate the error.

ERRORS

EACCES or EAGAIN: Operation is prohibited by locks held by other processes.
EAGAIN: The operation is prohibited because the file has been memor-mapped by another process.
EBADF: fd is not an open file descriptor
EINVAL: The value specified in op is not recognized by this kernel.

VERSIONS

POSIX.-2024 specifies FD_CLOFORK and F_DUPFD_CLOFORK, but Linux doesn't support them.

STANDARDS

POSIX.-2024.

HISTORY

4.3BSD, SVr4, POSIX.-1988.

Index

Duplicating a file descriptor
File descriptor flags
File status flags
Advisory record locking
Open file description locks (non-POSIX)
Managing signals
Leases
Delegations
File and directory change notification (dnotify)
Changing the capacity of a pipe
File Sealing
File read/write hints