rtime(3) Library Functions Manual rtime(3)
NAME
rtime - get time from a remote machine
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <rpc/auth_des.h>
int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
struct rpc_timeval *timeout);
DESCRIPTION
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 or-
der 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. Oth-
erwise, the tcp/time socket (port 37) is used.
RETURN VALUE
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.
ERRORS
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.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│rtime() │ Thread safety │ MT-Safe │
└────────────────────────────────────────────┴───────────────┴─────────┘
NOTES
Only IPv4 is supported.
Some in.timed versions support only TCP. Try the example program with
use_tcp set to 1.
BUGS
rtime() in glibc 2.2.5 and earlier does not work properly on 64-bit ma-
chines.
EXAMPLES
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);
}
SEE ALSO
ntpdate(1), inetd(8)
Linux man-pages 6.03 2022-12-15 rtime(3)
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