'\" et .TH fcntl.h "0P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual" .\" .SH PROLOG This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux. .\" .SH NAME fcntl.h \(em file control options .SH SYNOPSIS .LP .nf #include .fi .SH DESCRIPTION The .IR header shall define the following symbolic constants for the .IR cmd argument used by \fIfcntl\fR(). The values shall be unique and shall be suitable for use in .BR #if preprocessing directives. .IP F_DUPFD 12 Duplicate file descriptor. .IP F_DUPFD_CLOEXEC 12 .br Duplicate file descriptor with the close-on-\c .IR exec flag FD_CLOEXEC set. .IP F_GETFD 12 Get file descriptor flags. .IP F_SETFD 12 Set file descriptor flags. .IP F_GETFL 12 Get file status flags and file access modes. .IP F_SETFL 12 Set file status flags. .IP F_GETLK 12 Get record locking information. .IP F_SETLK 12 Set record locking information. .IP F_SETLKW 12 Set record locking information; wait if blocked. .IP F_GETOWN 12 Get process or process group ID to receive SIGURG signals. .IP F_SETOWN 12 Set process or process group ID to receive SIGURG signals. .P The .IR header shall define the following symbolic constant used for the \fIfcntl\fR() file descriptor flags, which shall be suitable for use in .BR #if preprocessing directives. .IP FD_CLOEXEC 12 Close the file descriptor upon execution of an .IR exec family function. .P The .IR header shall also define the following symbolic constants for the .IR l_type argument used for record locking with \fIfcntl\fR(). The values shall be unique and shall be suitable for use in .BR #if preprocessing directives. .IP F_RDLCK 12 Shared or read lock. .IP F_UNLCK 12 Unlock. .IP F_WRLCK 12 Exclusive or write lock. .P The .IR header shall define the values used for .IR l_whence , SEEK_SET, SEEK_CUR, and SEEK_END as described in .IR . .P The .IR header shall define the following symbolic constants as file creation flags for use in the .IR oflag value to \fIopen\fR() and \fIopenat\fR(). The values shall be bitwise-distinct and shall be suitable for use in .BR #if preprocessing directives. .IP O_CLOEXEC 12 The FD_CLOEXEC flag associated with the new descriptor shall be set to close the file descriptor upon execution of an .IR exec family function. .IP O_CREAT 12 Create file if it does not exist. .IP O_DIRECTORY 12 Fail if file is a non-directory file. .IP O_EXCL 12 Exclusive use flag. .IP O_NOCTTY 12 Do not assign controlling terminal. .IP O_NOFOLLOW 12 Do not follow symbolic links. .IP O_TRUNC 12 Truncate flag. .IP O_TTY_INIT 12 Set the .BR termios structure terminal parameters to a state that provides conforming behavior; see .IR "Section 11.2" ", " "Parameters that Can be Set". .P The O_TTY_INIT flag can have the value zero and in this case it need not be bitwise-distinct from the other flags. .P The .IR header shall define the following symbolic constants for use as file status flags for \fIopen\fR(), \fIopenat\fR(), and \fIfcntl\fR(). The values shall be suitable for use in .BR #if preprocessing directives. .IP O_APPEND 12 Set append mode. .IP O_DSYNC 12 Write according to synchronized I/O data integrity completion. .IP O_NONBLOCK 12 Non-blocking mode. .IP O_RSYNC 12 Synchronized read I/O operations. .IP O_SYNC 12 Write according to synchronized I/O file integrity completion. .P The .IR header shall define the following symbolic constant for use as the mask for file access modes. The value shall be suitable for use in .BR #if preprocessing directives. .IP O_ACCMODE 12 Mask for file access modes. .P The .IR header shall define the following symbolic constants for use as the file access modes for \fIopen\fR(), \fIopenat\fR(), and \fIfcntl\fR(). The values shall be unique, except that O_EXEC and O_SEARCH may have equal values. The values shall be suitable for use in .BR #if preprocessing directives. .IP O_EXEC 12 Open for execute only (non-directory files). The result is unspecified if this flag is applied to a directory. .IP O_RDONLY 12 Open for reading only. .IP O_RDWR 12 Open for reading and writing. .IP O_SEARCH 12 Open directory for search only. The result is unspecified if this flag is applied to a non-directory file. .IP O_WRONLY 12 Open for writing only. .P The .IR header shall define the symbolic constants for file modes for use as values of .BR mode_t as described in .IR . .P The .IR header shall define the following symbolic constant as a special value used in place of a file descriptor for the .IR *at (\|) functions which take a directory file descriptor as a parameter: .IP AT_FDCWD 12 Use the current working directory to determine the target of relative file paths. .P The .IR header shall define the following symbolic constant as a value for the .IR flag used by \fIfaccessat\fR(): .IP AT_EACCESS 12 Check access using effective user and group ID. .P The .IR header shall define the following symbolic constant as a value for the .IR flag used by \fIfstatat\fR(), \fIfchmodat\fR(), \fIfchownat\fR(), and \fIutimensat\fR(): .IP AT_SYMLINK_NOFOLLOW 12 .br Do not follow symbolic links. .P The .IR header shall define the following symbolic constant as a value for the flag used by \fIlinkat\fR(): .IP AT_SYMLINK_FOLLOW 12 .br Follow symbolic link. .br .P The .IR header shall define the following symbolic constant as a value for the flag used by \fIunlinkat\fR(): .IP AT_REMOVEDIR 12 .br Remove directory instead of file. .P The .IR header shall define the following symbolic constants for the .IR advice argument used by \fIposix_fadvise\fR(): .IP POSIX_FADV_DONTNEED 6 .br The application expects that it will not access the specified data in the near future. .IP POSIX_FADV_NOREUSE 6 .br The application expects to access the specified data once and then not reuse it thereafter. .IP POSIX_FADV_NORMAL 6 .br The application has no advice to give on its behavior with respect to the specified data. It is the default characteristic if no advice is given for an open file. .IP POSIX_FADV_RANDOM 6 .br The application expects to access the specified data in a random order. .IP POSIX_FADV_SEQUENTIAL 6 .br The application expects to access the specified data sequentially from lower offsets to higher offsets. .IP POSIX_FADV_WILLNEED 6 .br The application expects to access the specified data in the near future. .P The .IR header shall define the .BR flock structure describing a file lock. It shall include the following members: .sp .RS 4 .nf short l_type \fRType of lock; F_RDLCK, F_WRLCK, F_UNLCK.\fR short l_whence \fRFlag for starting offset.\fR off_t l_start \fRRelative offset in bytes.\fR off_t l_len \fRSize; if 0 then until EOF.\fR pid_t l_pid \fRProcess ID of the process holding the lock; returned with F_GETLK.\fR .fi .P .RE .P The .IR header shall define the .BR mode_t , .BR off_t , and .BR pid_t types as described in .IR . .P The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided. .sp .RS 4 .nf int creat(const char *, mode_t); int fcntl(int, int, ...); int open(const char *, int, ...); int openat(int, const char *, int, ...); int posix_fadvise(int, off_t, off_t, int); int posix_fallocate(int, off_t, off_t); .fi .P .RE .P Inclusion of the .IR header may also make visible all symbols from .IR and .IR . .LP .IR "The following sections are informative." .SH "APPLICATION USAGE" Although no existing implementation defines AT_SYMLINK_FOLLOW and AT_SYMLINK_NOFOLLOW as the same numeric value, POSIX.1\(hy2008 does not prohibit that as the two constants are not used with the same interfaces. .SH RATIONALE While many of the symbolic constants introduced in the .IR header do not strictly need to be used in .BR #if preprocessor directives, widespread historic practice has defined them as macros that are usable in such constructs, and examination of existing applications has shown that they are occasionally used in such a way. Therefore it was decided to retain this requirement on an implementation in POSIX.1\(hy2008. .SH "FUTURE DIRECTIONS" None. .SH "SEE ALSO" .IR "\fB\fP", .IR "\fB\fP", .IR "\fB\fP", .IR "\fB\fP" .P The System Interfaces volume of POSIX.1\(hy2017, .IR "\fIcreat\fR\^(\|)", .IR "\fIexec\fR\^", .IR "\fIfcntl\fR\^(\|)", .IR "\fIfutimens\fR\^(\|)", .IR "\fIopen\fR\^(\|)", .IR "\fIposix_fadvise\fR\^(\|)", .IR "\fIposix_fallocate\fR\^(\|)", .IR "\fIposix_madvise\fR\^(\|)" .\" .SH COPYRIGHT Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at http://www.opengroup.org/unix/online.html . .PP Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .