blob: 70f829e7fec79f800d6ac9ca0c363b8a3334ee9b [file] [log] [blame]
/* vi: set sw=4 ts=4: */
* The Rdate command will ask a time server for the RFC 868 time
* and optionally set the system time.
* by Sterling Huxley <>
* Licensed under GPLv2 or later, see file LICENSE in this source tree.
//config:config RDATE
//config: bool "rdate (5.6 kb)"
//config: default y
//config: help
//config: The rdate utility allows you to synchronize the date and time of your
//config: system clock with the date and time of a remote networked system using
//config: the RFC868 protocol, which is built into the inetd daemon on most
//config: systems.
//kbuild:lib-$(CONFIG_RDATE) += rdate.o
//usage:#define rdate_trivial_usage
//usage: "[-s/-p] HOST"
//usage:#define rdate_full_usage "\n\n"
//usage: "Set and print time from HOST using RFC 868\n"
//usage: "\n -s Only set system time"
//usage: "\n -p Only print time"
#include "libbb.h"
enum { RFC_868_BIAS = 2208988800UL };
static void socket_timeout(int sig UNUSED_PARAM)
bb_error_msg_and_die("timeout connecting to time server");
static time_t askremotedate(const char *host)
uint32_t nett;
int fd;
/* Timeout for dead or inaccessible servers */
signal(SIGALRM, socket_timeout);
fd = create_and_connect_stream_or_die(host, bb_lookup_std_port("time", "tcp", 37));
if (safe_read(fd, &nett, 4) != 4) /* read time from server */
bb_error_msg_and_die("%s: %s", host, "short read");
/* Convert from network byte order to local byte order.
* RFC 868 time is seconds since 1900-01-01 00:00 GMT.
* RFC 868 time 2,208,988,800 corresponds to 1970-01-01 00:00 GMT.
* Subtract the RFC 868 time to get Linux epoch.
nett = ntohl(nett) - RFC_868_BIAS;
if (sizeof(time_t) > 4) {
/* Now we have 32-bit lsb of a wider time_t
* Imagine that nett = 0x00000001,
* current time cur = 0x123ffffffff.
* Assuming our time is not some 40 years off,
* remote time must be 0x12400000001.
* Need to adjust our time by (int32_t)(nett - cur).
time_t cur = time(NULL);
int32_t adjust = (int32_t)(nett - (uint32_t)cur);
return cur + adjust;
/* This is not going to work, but what can we do */
return (time_t)nett;
int rdate_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
int rdate_main(int argc UNUSED_PARAM, char **argv)
time_t remote_time;
unsigned flags;
flags = getopt32(argv, "^" "sp" "\0" "-1");
remote_time = askremotedate(argv[optind]);
/* Manpages of various Unixes are confusing. What happens is:
* (no opts) set and print time
* -s: set time ("do not print the time")
* -p: print time ("do not set, just print the remote time")
* -sp: print time (that's what we do, not sure this is right)
if (!(flags & 2)) { /* no -p (-s may be present) */
if (time(NULL) == remote_time)
bb_error_msg("current time matches remote time");
if (stime(&remote_time) < 0)
bb_perror_msg_and_die("can't set time of day");
if (flags != 1) /* not lone -s */
printf("%s", ctime(&remote_time));