1rtime(3)                   Library Functions Manual                   rtime(3)
2
3
4

NAME

6       rtime - get time from a remote machine
7

LIBRARY

9       Standard C library (libc, -lc)
10

SYNOPSIS

12       #include <rpc/auth_des.h>
13
14       int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
15                 struct rpc_timeval *timeout);
16

DESCRIPTION

18       This  function uses the Time Server Protocol as described in RFC 868 to
19       obtain the time from a remote machine.
20
21       The Time Server Protocol gives the time in seconds since 00:00:00  UTC,
22       1 Jan 1900, and this function subtracts the appropriate constant in or‐
23       der to convert the  result  to  seconds  since  the  Epoch,  1970-01-01
24       00:00:00 +0000 (UTC).
25
26       When  timeout is non-NULL, the udp/time socket (port 37) is used.  Oth‐
27       erwise, the tcp/time socket (port 37) is used.
28

RETURN VALUE

30       On success, 0 is returned, and the obtained 32-bit time value is stored
31       in timep->tv_sec.  In case of error -1 is returned, and errno is set to
32       indicate the error.
33

ERRORS

35       All errors for underlying functions (sendto(2),  poll(2),  recvfrom(2),
36       connect(2), read(2)) can occur.  Moreover:
37
38       EIO    The number of returned bytes is not 4.
39
40       ETIMEDOUT
41              The waiting time as defined in timeout has expired.
42

ATTRIBUTES

44       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
45       tributes(7).
46
47       ┌────────────────────────────────────────────┬───────────────┬─────────┐
48Interface                                   Attribute     Value   
49       ├────────────────────────────────────────────┼───────────────┼─────────┤
50rtime()                                     │ Thread safety │ MT-Safe │
51       └────────────────────────────────────────────┴───────────────┴─────────┘
52

NOTES

54       Only IPv4 is supported.
55
56       Some in.timed versions support only TCP.  Try the example program  with
57       use_tcp set to 1.
58

BUGS

60       rtime() in glibc 2.2.5 and earlier does not work properly on 64-bit ma‐
61       chines.
62

EXAMPLES

64       This example requires that port 37 is up and open.  You may check  that
65       the time entry within /etc/inetd.conf is not commented out.
66
67       The  program  connects to a computer called "linux".  Using "localhost"
68       does not work.  The result is the localtime of the computer "linux".
69
70       #include <errno.h>
71       #include <netdb.h>
72       #include <stdio.h>
73       #include <stdlib.h>
74       #include <string.h>
75       #include <time.h>
76
77       #include <rpc/auth_des.h>
78
79       static int use_tcp = 0;
80       static const char servername[] = "linux";
81
82       int
83       main(void)
84       {
85           int                 ret;
86           time_t              t;
87           struct hostent      *hent;
88           struct rpc_timeval  time1 = {0, 0};
89           struct rpc_timeval  timeout = {1, 0};
90           struct sockaddr_in  name;
91
92           memset(&name, 0, sizeof(name));
93           sethostent(1);
94           hent = gethostbyname(servername);
95           memcpy(&name.sin_addr, hent->h_addr, hent->h_length);
96
97           ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
98           if (ret < 0)
99               perror("rtime error");
100           else {
101               t = time1.tv_sec;
102               printf("%s\n", ctime(&t));
103           }
104
105           exit(EXIT_SUCCESS);
106       }
107

SEE ALSO

109       ntpdate(1), inetd(8)
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111
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113Linux man-pages 6.04              2022-12-15                          rtime(3)
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