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/auth_des.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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ATTRIBUTES

41       For   an   explanation   of   the  terms  used  in  this  section,  see
42       attributes(7).
43
44       ┌──────────┬───────────────┬─────────┐
45       │Interface │ Attribute     │ Value   │
46       ├──────────┼───────────────┼─────────┤
47       │rtime()   │ Thread safety │ MT-Safe │
48       └──────────┴───────────────┴─────────┘

NOTES

50       Only IPv4 is supported.
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52       Some in.timed versions support only TCP.  Try the example program  with
53       use_tcp set to 1.
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55       Libc5 uses the prototype
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57           int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
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59       and requires <sys/time.h> instead of <rpc/auth_des.h>.
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BUGS

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

66       This example requires that port 37 is up and open.  You may check  that
67       the time entry within /etc/inetd.conf is not commented out.
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69       The  program  connects to a computer called "linux".  Using "localhost"
70       does not work.  The result is the localtime of the computer "linux".
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72       #include <stdio.h>
73       #include <stdlib.h>
74       #include <errno.h>
75       #include <string.h>
76       #include <time.h>
77       #include <rpc/auth_des.h>
78       #include <netdb.h>
79
80       static int use_tcp = 0;
81       static char *servername = "linux";
82
83       int
84       main(void)
85       {
86           struct sockaddr_in name;
87           struct rpc_timeval time1 = {0,0};
88           struct rpc_timeval timeout = {1,0};
89           struct hostent *hent;
90           int ret;
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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               time_t t = time1.tv_sec;
102               printf("%s\n", ctime(&t));
103           }
104
105           exit(EXIT_SUCCESS);
106       }
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COLOPHON

112       This page is part of release 4.15 of the Linux  man-pages  project.   A
113       description  of  the project, information about reporting bugs, and the
114       latest    version    of    this    page,    can     be     found     at
115       https://www.kernel.org/doc/man-pages/.
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119GNU                               2017-09-15                          RTIME(3)