shutdown(2)

Purpose

shutdown() shuts down all or part of the full-duplex connection on the socket associated with sockfd. Unlike close(2) it acts per direction and affects the connection, not the descriptor: other processes holding dups of the fd see the shutdown too.

Synopsis

#include <sys/socket.h>
int shutdown(int sockfd, int how);

Arguments and behavior

The constants have the values 0, 1, 2 and are defined in <sys/socket.h> since glibc 2.1.91 (shutdown.2 NOTES). Typical TCP use: SHUT_WR to send a FIN while still reading, letting the peer drain and respond.

Return value and errors

Zero on success; -1 with errno (shutdown.2): EBADF, EINVAL (invalid how – but see BUGS note below), ENOTCONN (socket not connected), ENOTSOCK.

Flags and constants

SHUT_RD / SHUT_WR / SHUT_RDWR as in the table above; no bit flags exist beyond the three how values.

Security and notes

Validity checking of how is done in domain-specific code, and before Linux 3.7 not all domains performed the checks – most notably UNIX domain sockets simply ignored invalid values; this was fixed for UNIX domain (and DECnet) sockets in Linux 3.7 (shutdown.2 BUGS, with commit fc61b928dc4d cited there). shutdown() does not free the fd; close(2) is still required. On a stream socket whose local end was shut down, sendto fails with EPIPE and raises SIGPIPE unless MSG_NOSIGNAL is set (send.2).

References

• Cached man page: source-cache/man-pages-sparse/man2/shutdown.2.
• Numbers: hub overview.md; source-cache/kernel/syscall_{64,32,generic,arm}.tbl.
• Hub row: overview.