rtime(3)

1RTIME(3)                   Linux Programmer's Manual                  RTIME(3)
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NAME

6       rtime - get time from a remote machine
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SYNOPSIS

9       #include <rpc/des_crypt.h>
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11       int rtime(struct sockaddr_in *addrp, struct rpc_timeval *timep,
12                 struct rpc_timeval *timeout);
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DESCRIPTION

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

27       On success, 0 is returned, and the obtained 32-bit time value is stored
28       in  timep->tv_sec.   In  case of error -1 is returned, and errno is set
29       appropriately.
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ERRORS

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

41       Only IPv4 is supported.
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43       Some  in.timed versions support only TCP.  Try the example program with
44       use_tcp set to 1.
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46       Libc5 uses the prototype
47       int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
48       and requires <sys/time.h> instead of <rpc/auth_des.h>.
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BUGS

51       rtime() in glibc 2.2.5 and earlier does not  work  properly  on  64-bit
52       machines.
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EXAMPLE

55       This  example requires that port 37 is up and open.  You may check that
56       the time entry within /etc/inetd.conf is not commented out.
57       The program connects to a computer called "linux".   Using  "localhost"
58       does not work.  The result is the localtime of the computer "linux".
59
60       #include <stdio.h>
61       #include <stdlib.h>
62       #include <errno.h>
63       #include <string.h>
64       #include <time.h>
65       #include <rpc/auth_des.h>
66       #include <netdb.h>
67
68       int use_tcp = 0;
69       char *servername = "linux";
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71       int
72       main(void)
73       {
74           struct sockaddr_in name;
75           struct rpc_timeval time1 = {0,0};
76           struct rpc_timeval timeout = {1,0};
77           struct hostent *hent;
78           int ret;
79
80           memset(&name, 0, sizeof(name));
81           sethostent(1);
82           hent = gethostbyname(servername);
83           memcpy(&name.sin_addr, hent->h_addr, hent->h_length);
84
85           ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
86           if (ret < 0)
87               perror("rtime error");
88           else {
89            time_t t = time1.tv_sec;
90               printf("%s\n", ctime(&t));
91           }
92
93           exit(EXIT_SUCCESS);
94       }
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COLOPHON

100       This  page  is  part of release 3.53 of the Linux man-pages project.  A
101       description of the project, and information about reporting  bugs,  can
102       be found at http://www.kernel.org/doc/man-pages/.
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106GNU                               2012-08-03                          RTIME(3)