blob: 8dd784d3d68e91cc1d6cb398d81a299809486016 [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"
//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: "[-sp] HOST"
//usage:#define rdate_full_usage "\n\n"
//usage: "Get and possibly set system time from a remote HOST\n"
//usage: "\n -s Set system time (default)"
//usage: "\n -p 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;
/* Add a timeout for dead or inaccessible servers */
signal(SIGALRM, socket_timeout);
fd = create_and_connect_stream_or_die(host, bb_lookup_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 the number of seconds
* since 00:00 (midnight) 1 January 1900 GMT
* the RFC 868 time 2,208,988,800 corresponds to 00:00 1 Jan 1970 GMT
* Subtract the RFC 868 time to get Linux epoch.
return ntohl(nett) - RFC_868_BIAS;
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;
opt_complementary = "-1";
flags = getopt32(argv, "sp");
remote_time = askremotedate(argv[optind]);
if (!(flags & 2)) { /* no -p (-s may be present) */
time_t current_time;
if (current_time == 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));