Editing File descriptor (section)

==Operations on file descriptors==
The following lists typical operations on file descriptors on modern [[Unix-like]] systems. Most of these functions are declared in the <code><unistd.h></code> header, but some are in the <code><fcntl.h></code> header instead.

===Creating file descriptors===
*{{mono|[[open (system call)|open]]()}}
*{{mono|creat()}}<!-- Not a typo --><ref>{{cite web |url=http://pubs.opengroup.org/onlinepubs/9699919799/functions/creat.html |title=The Open Group Base Specifications Issue 7, IEEE Std 1003.1-2008, 2018 Edition – creat |author=The Open Group |access-date=2019-04-11 |author-link=The Open Group }}</ref>
*{{mono|socket()}}
*{{mono|accept()}}
*{{mono|socketpair()}}
*{{mono|pipe()}}
*{{mono|epoll_create()}} (Linux)
*{{mono|signalfd()}} (Linux)
*{{mono|eventfd()}} (Linux)
*{{mono|timerfd_create()}} (Linux)
*{{mono|memfd_create()}} (Linux)
*{{mono|userfaultfd()}} (Linux)
*{{mono|fanotify_init()}} (Linux)
*{{mono|inotify_init()}} (Linux)
*{{mono|clone()}} (with flag CLONE_PIDFD, Linux)
*{{mono|pidfd_open()}} (Linux)
*{{mono|open_by_handle_at()}} (Linux)
*{{mono|kqueue()}} (BSD)
*{{mono|pdfork()}} (kFreeBSD)

===Deriving file descriptors===
*{{mono|dirfd()}}
*{{mono|fileno()}}

===Operations on a single file descriptor===
*{{mono|[[read (system call)|read]](), [[write (system call)|write]]()}}
*{{mono|readv()}}, {{mono|writev()}}
*{{mono|pread()}}, {{mono|pwrite()}}
*{{mono|recv()}}, {{mono|send()}}
*{{mono|recvfrom()}}, {{mono|sendto()}}
*{{mono|recvmsg()}}, {{mono|sendmsg()}} (also used for sending FDs to other processes over a Unix domain socket)
*{{mono|recvmmsg()}}, {{mono|sendmmsg()}}
*{{mono|lseek()}}, {{mono|llseek()}}
*{{mono|[[stat (system call)|fstat()]]}}
*{{mono|fstatvfs()}}
*{{mono|fchmod()}}
*{{mono|fchown()}}
*{{mono|ftruncate()}}
*{{mono|fsync()}}
*{{mono|fdatasync()}}
*{{mono|fdopendir()}}
*{{mono|fgetxattr()}}, {{mono|fsetxattr()}} (Linux)
*{{mono|flistxattr()}}, {{mono|fremovexattr()}} (Linux)
*{{mono|statx}} (Linux)
*{{mono|setns}} (Linux)
*{{mono|vmsplice()}} (Linux)
*{{mono|pidfd_send_signal()}} (Linux)
*{{mono|pdkill()}} (kFreeBSD)
*{{mono|waitid()}} (with P_PIDFD ID type, Linux)
*{{mono|fdopen()}} (stdio function:converts file descriptor to FILE*)
*{{mono|dprintf()}} (stdio function: prints to file descriptor)

===Operations on multiple file descriptors===
*[[select (Unix)|{{mono|select()}}]], {{mono|pselect()}}
*[[poll (Unix)|{{mono|poll()}}]], {{mono|ppoll()}}
*{{mono|epoll_wait()}}, {{mono|epoll_pwait()}}, {{mono|epoll_pwait2()}} (Linux, takes a single epoll filedescriptor to wait on many other file descriptors)
*[[Epoll|{{mono|epoll_ctl()}}]] (for Linux)
*[[Kqueue|{{mono|kqueue()}}]] (for BSD-based systems).
*{{mono|sendfile()}}
*[[splice (system call)|{{mono|splice()}}]], {{mono|tee()}} (for Linux)
*{{mono|copy_file_range()}} (for Linux)

===Operations on the file descriptor table===
The {{mono|fcntl()}} function is used to perform various operations on a file descriptor, depending on the command argument passed to it. There are commands to get and set attributes associated with a file descriptor, including {{mono|F_GETFD, F_SETFD, F_GETFL}} and {{mono|F_SETFL}}.

*{{mono|[[close (system call)|close()]]}}
*{{mono|closefrom()}} (BSD and Solaris only; deletes all file descriptors greater than or equal to specified number)
*{{mono|close_range()}} (for Linux)<ref>{{cite web |url=https://man7.org/linux/man-pages/man2/close_range.2.html |title=close_range(2) — Linux manual page |author=Stephen Kitt, Michael Kerrisk |access-date=2021-03-22 }}</ref>
*{{mono|[[dup (system call)|dup()]]}} (duplicates an existing file descriptor guaranteeing to be the lowest number available file descriptor)
*{{mono|[[dup2]]()}}, {{mono|[[Dup2|dup3()]]}} (Close fd1 if necessary, and make file descriptor fd1 point to the open file of fd2)
*{{mono|fcntl (F_DUPFD)}}

===Operations that modify process state===
*{{mono|fchdir()}} (sets the process's current working directory based on a directory file descriptor)
*{{mono|[[mmap]]()}} (maps ranges of a file into the process's address space)

===File locking===
* {{mono|flock()}}
* {{mono|fcntl() (F_GETLK, F_SETLK}} and {{mono|F_SETLKW)}}
* {{mono|lockf()}}

===Sockets===
{{See also|Berkeley sockets}}
*{{mono|connect()}}
*{{mono|bind()}}
*{{mono|listen()}}
*{{mono|accept()}} (creates a new file descriptor for an incoming connection)
*{{mono|getsockname()}}
*{{mono|getpeername()}}
*{{mono|getsockopt()}}
*{{mono|setsockopt()}}
*{{mono|shutdown()}} (shuts down one or both halves of a full duplex connection)

===Miscellaneous===
*[[ioctl|{{mono|ioctl()}}]] (a large collection of miscellaneous operations on a single file descriptor, often associated with a device)