.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH IP_MTU 2const 2025-11-25 "Linux man-pages 6.17"
.SH NAME
IP_MTU
\-
path maximum transmission unit size
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#include <netinet/in.h>" "  /* Definition of " IP* " constants */"
.B #include <sys/socket.h>
.P
.BI int\~getsockopt(int\~ sockfd ,\~IPPROTO_IP,\~IP_MTU,
.BI "               int\~*" val ,\~sizeof(int));
.fi
.SH DESCRIPTION
Retrieve the current known path MTU of the current socket.
.P
.B IP_MTU
is valid only for
.BR getsockopt (2),
and can be employed only when the socket has been connected.
.SH ERRORS
See
.BR IPPROTO_IP (2const).
See
.BR getsockopt (2).
See
.BR ip (7).
.SH STANDARDS
Linux.
.SH HISTORY
Linux 2.2.
.\" Precisely: since Linux 2.1.124
.SH SEE ALSO
.BR IPPROTO_IP (2const),
.BR getsockopt (2),
.BR ip (7)