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NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |ATTRIBUTES |NOTES |BUGS |EXAMPLES |SEE ALSO |COLOPHON | |
rtime(3) Library Functions Manualrtime(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). Whentimeout 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 intimep->tv_sec. In case of error -1 is returned, anderrno is set to indicate the error.
All errors for underlying functions (sendto(2),poll(2),recvfrom(2),connect(2),read(2)) can occur. Moreover:EIOThe 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, seeattributes(7). ┌──────────────────────────────────────┬───────────────┬─────────┐ │Interface│Attribute│Value│ ├──────────────────────────────────────┼───────────────┼─────────┤ │rtime() │ Thread safety │ MT-Safe │ └──────────────────────────────────────┴───────────────┴─────────┘
Only IPv4 is supported. Somein.timed versions support only TCP. Try the example program withuse_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 theman-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- to-date source for the page, or you have corrections or improvements to the information in this COLOPHON (which isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17rtime(3)HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |