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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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rtime(3) Library Functions Manual rtime(3)
rtime - get time from a remote machine
Standard C library (libc, -lc)
#include <rpc/auth_des.h>
int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
struct rpc_timeval *timeout);
This function uses the Time Server Protocol as described in
RFC 868 to obtain the time from a remote machine.
The Time Server Protocol gives the time in seconds since 00:00:00
UTC, 1 Jan 1900, and this function subtracts the appropriate
constant in order to convert the result to seconds since the
Epoch, 1970-01-01 00:00:00 +0000 (UTC).
When timeout is non-NULL, the udp/time socket (port 37) is used.
Otherwise, the tcp/time socket (port 37) is used.
On success, 0 is returned, and the obtained 32-bit time value is
stored in timep->tv_sec. In case of error -1 is returned, and
errno is set to indicate the error.
All errors for underlying functions (sendto(2), poll(2),
recvfrom(2), connect(2), read(2)) can occur. Moreover:
EIO The number of returned bytes is not 4.
ETIMEDOUT
The waiting time as defined in timeout has expired.
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────────┼───────────────┼─────────┤
│ rtime() │ Thread safety │ MT-Safe │
└──────────────────────────────────────┴───────────────┴─────────┘
Only IPv4 is supported.
Some in.timed versions support only TCP. Try the example program
with use_tcp set to 1.
rtime() in glibc 2.2.5 and earlier does not work properly on
64-bit machines.
This example requires that port 37 is up and open. You may check
that the time entry within /etc/inetd.conf is not commented out.
The program connects to a computer called "linux". Using
"localhost" does not work. The result is the localtime of the
computer "linux".
#include <errno.h>
#include <netdb.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <rpc/auth_des.h>
static int use_tcp = 0;
static const char servername[] = "linux";
int
main(void)
{
int ret;
time_t t;
struct hostent *hent;
struct rpc_timeval time1 = {0, 0};
struct rpc_timeval timeout = {1, 0};
struct sockaddr_in name;
memset(&name, 0, sizeof(name));
sethostent(1);
hent = gethostbyname(servername);
memcpy(&name.sin_addr, hent->h_addr, hent->h_length);
ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
if (ret < 0)
perror("rtime error");
else {
t = time1.tv_sec;
printf("%s\n", ctime(&t));
}
exit(EXIT_SUCCESS);
}
ntpdate(1), inetd(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
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improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 rtime(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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