man3/rtime.3

   1 .\" Copyright 2003 walter harms (walter.harms@informatik.uni-oldenburg.de)
   2 .\" Distributed under GPL
   3 .\" Modified 2003-04-04 Walter Harms
   4 .\" <walter.harms@informatik.uni-oldenburg.de>
   5 .\"
   6 .\" Slightly polished, aeb, 2003-04-06
   7 .\"
   8 .TH RTIME 3 2008-07-12 "GNU" "Linux Programmer's Manual"
   9 .SH NAME
  10 rtime \- get time from a remote machine
  11 .SH SYNOPSIS
  12 .nf
  13 .B "#include <rpc/des_crypt.h>"
  14 .sp
  15 .BI "int rtime(struct sockaddr_in *" addrp ", struct rpc_timeval *" timep ,
  16 .BI "          struct rpc_timeval *" timeout );
  17 .fi
  18 .SH DESCRIPTION
  19 This function uses the Time Server Protocol as described in
  20 RFC\ 868 to obtain the time from a remote machine.
  21 .LP
  22 The Time Server Protocol gives the time in seconds since
  23 00:00:00 UTC, 1 Jan 1900,
  24 and this function subtracts the appropriate constant in order to
  25 convert the result to seconds since the Epoch,
  26 1970-01-01 00:00:00 +0000 (UTC).
  27 .LP
  28 When
  29 .I timeout
  30 is non-NULL, the udp/time socket (port 37) is used.
  31 Otherwise, the tcp/time socket (port 37) is used.
  32 .SH "RETURN VALUE"
  33 On success, 0 is returned, and the obtained 32-bit time value is stored in
  34 .IR timep\->tv_sec .
  35 In case of error \-1 is returned, and
  36 .I errno
  37 is set appropriately.
  38 .SH ERRORS
  39 All errors for underlying functions
  40 .RB ( sendto (2),
  41 .BR poll (2),
  42 .BR recvfrom (2),
  43 .BR connect (2),
  44 .BR read (2))
  45 can occur.
  46 Moreover:
  47 .TP
  48 .B EIO
  49 The number of returned bytes is not 4.
  50 .TP
  51 .B ETIMEDOUT
  52 The waiting time as defined in timeout has expired.
  53 .SH "NOTES"
  54 Only IPv4 is supported.
  55 .LP
  56 Some
  57 .I in.timed
  58 versions only support TCP.
  59 Try the example program with
  60 .I use_tcp
  61 set to 1.
  62 .LP
  63 Libc5 uses the prototype
  64 .br
  65 int rtime(struct sockaddr_in *, struct timeval *, struct timeval *);
  66 .br
  67 and requires
  68 .I <sys/time.h>
  69 instead of
  70 .IR <rpc/auth_des.h> .
  71 .SH "BUGS"
  72 .BR rtime ()
  73 in glibc 2.2.5 and earlier does not work properly on 64-bit machines.
  74 .SH "EXAMPLE"
  75 This example requires that port 37 is up and open.
  76 You may check
  77 that the time entry within
  78 .I /etc/inetd.conf
  79 is not commented out.
  80 .br
  81 The program connects to a computer called "linux".
  82 Using "localhost" does not work.
  83 The result is the localtime of the computer "linux".
  84 .sp
  85 .nf
  86 #include <stdio.h>
  87 #include <stdlib.h>
  88 #include <errno.h>
  89 #include <string.h>
  90 #include <time.h>
  91 #include <rpc/auth_des.h>
  92 #include <netdb.h>
  93
  94 int use_tcp = 0;
  95 char *servername = "linux";
  96
  97 int
  98 main(void)
  99 {
 100     struct sockaddr_in name;
 101     struct rpc_timeval time1 = {0,0};
 102     struct rpc_timeval timeout = {1,0};
 103     struct hostent *hent;
 104     int ret;
 105
 106     memset((char *) &name, 0, sizeof(name));
 107     sethostent(1);
 108     hent = gethostbyname(servername);
 109     memcpy((char *) &name.sin_addr, hent\->h_addr, hent\->h_length);
 110
 111     ret = rtime(&name, &time1, use_tcp ? NULL : &timeout);
 112     if (ret < 0)
 113         perror("rtime error");
 114     else
 115         printf("%s\\n", ctime((time_t *) &time1.tv_sec));
 116
 117     exit(EXIT_SUCCESS);
 118 }
 119 .fi
 120 .SH "SEE ALSO"
 121 .\" .BR netdate (1),
 122 .BR ntpdate (1),
 123 .\" .BR rdate (1),
 124 .BR inetd (8)