man3/rtime.3

   1 .\" Copyright 2003 walter harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\"
   3 .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE)
   4 .\" Distributed under GPL
   5 .\" %%%LICENSE_END
   6 .\"
   7 .\" Modified 2003-04-04 Walter Harms
   8 .\" <walter.harms@informatik.uni-oldenburg.de>
   9 .\"
  10 .\" Slightly polished, aeb, 2003-04-06
  11 .\"
  12 .TH RTIME 3 2019-03-06 "GNU" "Linux Programmer's Manual"
  13 .SH NAME
  14 rtime \- get time from a remote machine
  15 .SH SYNOPSIS
  16 .nf
  17 .B "#include <rpc/auth_des.h>"
  18 .PP
  19 .BI "int rtime(struct sockaddr_in *" addrp ", struct rpc_timeval *" timep ,
  20 .BI "          struct rpc_timeval *" timeout );
  21 .fi
  22 .SH DESCRIPTION
  23 This function uses the Time Server Protocol as described in
  24 RFC\ 868 to obtain the time from a remote machine.
  25 .PP
  26 The Time Server Protocol gives the time in seconds since
  27 00:00:00 UTC, 1 Jan 1900,
  28 and this function subtracts the appropriate constant in order to
  29 convert the result to seconds since the
  30 Epoch, 1970-01-01 00:00:00 +0000 (UTC).
  31 .PP
  32 When
  33 .I timeout
  34 is non-NULL, the udp/time socket (port 37) is used.
  35 Otherwise, the tcp/time socket (port 37) is used.
  36 .SH RETURN VALUE
  37 On success, 0 is returned, and the obtained 32-bit time value is stored in
  38 .IR timep\->tv_sec .
  39 In case of error \-1 is returned, and
  40 .I errno
  41 is set appropriately.
  42 .SH ERRORS
  43 All errors for underlying functions
  44 .RB ( sendto (2),
  45 .BR poll (2),
  46 .BR recvfrom (2),
  47 .BR connect (2),
  48 .BR read (2))
  49 can occur.
  50 Moreover:
  51 .TP
  52 .B EIO
  53 The number of returned bytes is not 4.
  54 .TP
  55 .B ETIMEDOUT
  56 The waiting time as defined in timeout has expired.
  57 .SH ATTRIBUTES
  58 For an explanation of the terms used in this section, see
  59 .BR attributes (7).
  60 .TS
  61 allbox;
  62 lb lb lb
  63 l l l.
  64 Interface       Attribute       Value
  65 T{
  66 .BR rtime ()
  67 T}      Thread safety   MT-Safe
  68 .TE
  69 .SH NOTES
  70 Only IPv4 is supported.
  71 .PP
  72 Some
  73 .I in.timed
  74 versions support only TCP.
  75 Try the example program with
  76 .I use_tcp
  77 set to 1.
  78 .PP
  79 Libc5 uses the prototype
  80 .PP
  81 .nf
  82     int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
  83 .fi
  84 .PP
  85 and requires
  86 .I <sys/time.h>
  87 instead of
  88 .IR <rpc/auth_des.h> .
  89 .SH BUGS
  90 .BR rtime ()
  91 in glibc 2.2.5 and earlier does not work properly on 64-bit machines.
  92 .SH EXAMPLES
  93 This example requires that port 37 is up and open.
  94 You may check
  95 that the time entry within
  96 .I /etc/inetd.conf
  97 is not commented out.
  98 .PP
  99 The program connects to a computer called "linux".
 100 Using "localhost" does not work.
 101 The result is the localtime of the computer "linux".
 102 .PP
 103 .EX
 104 #include <stdio.h>
 105 #include <stdlib.h>
 106 #include <errno.h>
 107 #include <string.h>
 108 #include <time.h>
 109 #include <rpc/auth_des.h>
 110 #include <netdb.h>
 111
 112 static int use_tcp = 0;
 113 static char *servername = "linux";
 114
 115 int
 116 main(void)
 117 {
 118     struct sockaddr_in name;
 119     struct rpc_timeval time1 = {0,0};
 120     struct rpc_timeval timeout = {1,0};
 121     struct hostent *hent;
 122     int ret;
 123
 124     memset(&name, 0, sizeof(name));
 125     sethostent(1);
 126     hent = gethostbyname(servername);
 127     memcpy(&name.sin_addr, hent\->h_addr, hent\->h_length);
 128
 129     ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
 130     if (ret < 0)
 131         perror("rtime error");
 132     else {
 133         time_t t = time1.tv_sec;
 134         printf("%s\en", ctime(&t));
 135     }
 136
 137     exit(EXIT_SUCCESS);
 138 }
 139 .EE
 140 .SH SEE ALSO
 141 .\" .BR netdate (1),
 142 .BR ntpdate (1),
 143 .\" .BR rdate (1),
 144 .BR inetd (8)