LXR busybox/util-linux/rdate.c

   1/* vi: set sw=4 ts=4: */
   2/*
   3 * The Rdate command will ask a time server for the RFC 868 time
   4 * and optionally set the system time.
   5 *
   6 * by Sterling Huxley <sterling@europa.com>
   7 *
   8 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
   9 */
  10//config:config RDATE
  11//config:       bool "rdate (5.6 kb)"
  12//config:       default y
  13//config:       help
  14//config:       The rdate utility allows you to synchronize the date and time of your
  15//config:       system clock with the date and time of a remote networked system using
  16//config:       the RFC868 protocol, which is built into the inetd daemon on most
  17//config:       systems.
  18
  19//applet:IF_RDATE(APPLET(rdate, BB_DIR_USR_SBIN, BB_SUID_DROP))
  20
  21//kbuild:lib-$(CONFIG_RDATE) += rdate.o
  22
  23//usage:#define rdate_trivial_usage
  24//usage:       "[-s/-p] HOST"
  25//usage:#define rdate_full_usage "\n\n"
  26//usage:       "Set and print time from HOST using RFC 868\n"
  27//usage:     "\n        -s      Only set system time"
  28//usage:     "\n        -p      Only print time"
  29
  30#include "libbb.h"
  31
  32enum { RFC_868_BIAS = 2208988800UL };
  33
  34static void socket_timeout(int sig UNUSED_PARAM)
  35{
  36        bb_error_msg_and_die("timeout connecting to time server");
  37}
  38
  39static time_t askremotedate(const char *host)
  40{
  41        uint32_t nett;
  42        int fd;
  43
  44        /* Timeout for dead or inaccessible servers */
  45        alarm(10);
  46        signal(SIGALRM, socket_timeout);
  47
  48        fd = create_and_connect_stream_or_die(host, bb_lookup_std_port("time", "tcp", 37));
  49
  50        if (safe_read(fd, &nett, 4) != 4)    /* read time from server */
  51                bb_error_msg_and_die("%s: %s", host, "short read");
  52        if (ENABLE_FEATURE_CLEAN_UP)
  53                close(fd);
  54
  55        /* Convert from network byte order to local byte order.
  56         * RFC 868 time is seconds since 1900-01-01 00:00 GMT.
  57         * RFC 868 time 2,208,988,800 corresponds to 1970-01-01 00:00 GMT.
  58         * Subtract the RFC 868 time to get Linux epoch.
  59         */
  60        nett = ntohl(nett) - RFC_868_BIAS;
  61
  62        if (sizeof(time_t) > 4) {
  63                /* Now we have 32-bit lsb of a wider time_t
  64                 * Imagine that  nett =   0x00000001,
  65                 * current time  cur = 0x123ffffffff.
  66                 * Assuming our time is not some 40 years off,
  67                 * remote time must be 0x12400000001.
  68                 * Need to adjust our time by (int32_t)(nett - cur).
  69                 */
  70                time_t cur = time(NULL);
  71                int32_t adjust = (int32_t)(nett - (uint32_t)cur);
  72                return cur + adjust;
  73        }
  74        /* This is not going to work, but what can we do */
  75        return (time_t)nett;
  76}
  77
  78int rdate_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
  79int rdate_main(int argc UNUSED_PARAM, char **argv)
  80{
  81        time_t remote_time;
  82        unsigned flags;
  83
  84        flags = getopt32(argv, "^" "sp" "\0" "-1");
  85
  86        remote_time = askremotedate(argv[optind]);
  87
  88        /* Manpages of various Unixes are confusing. What happens is:
  89         * (no opts) set and print time
  90         * -s: set time ("do not print the time")
  91         * -p: print time ("do not set, just print the remote time")
  92         * -sp: print time (that's what we do, not sure this is right)
  93         */
  94
  95        if (!(flags & 2)) { /* no -p (-s may be present) */
  96                if (time(NULL) == remote_time)
  97                        bb_error_msg("current time matches remote time");
  98                else
  99                        if (stime(&remote_time) < 0)
 100                                bb_perror_msg_and_die("can't set time of day");
 101        }
 102
 103        if (flags != 1) /* not lone -s */
 104                printf("%s", ctime(&remote_time));
 105
 106        return EXIT_SUCCESS;
 107}
 108