rtime(3) - f34

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 or‐
20       der 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 at‐
42       tributes(7).
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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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BUGS

56       rtime() in glibc 2.2.5 and earlier does not work properly on 64-bit ma‐
57       chines.
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EXAMPLES

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

106       This page is part of release 5.10 of the Linux  man-pages  project.   A
107       description  of  the project, information about reporting bugs, and the
108       latest    version    of    this    page,    can     be     found     at
109       https://www.kernel.org/doc/man-pages/.
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113GNU                               2020-12-21                          RTIME(3)