A web page with a shell script fron end to be run by cron, assuming a uucp connection with other machines whose clocks are to be synchronized with a central machine. There are three files, internally documented, two of which are C programs that need to be compiled.

This is useful with a system of local machines that are set up with uucp connection, so tht only the master machine needs to have its clock set; synchrosys propagates the the time setting to the other machines. My experience has been that the synchronization cab be had to within less than five seconds.

:
# synchrosys
#
# Synchronize the clock of a named remote slave system with the current
# system clock.
#
# Cf. /etc/etime, /etc/ssyndemon (other parts of this synchronizing system)
#
if [ $# -eq 0 ]; then
	echo "synchrosys: remote system name argument missing"
	exit 1
fi
if [ $# -gt 1 ]; then
	echo "synchrosys: too many remote system names"
	exit 1
fi
#

#
# NB As point of secure operation we should hold up here in a loop until
#    the disappearance of a lockfile in /usr/spool/uucp.

#
# Estimate of how long it will take to activate uux, call another system,
# login and secure a uux execution of the daemon 'ssyndemon'.
#
ADVANCE_SECS=50

# NB 777 on TDIR and path to it must be maintained.
TDIR=/usr/tmp
TFILE=ssyndf
DAEMON=/etc/ssyndemon
#
#
# Note:
# It Appears that (local trantor=systemid system) loses about 2 mins per week.
#

#
# Form the argument to be picked up by the daemon on the remote system
#

SETTIME=`/etc/etime $ADVANCE_SECS`

cd $TDIR
echo "$SETTIME\c" > $TFILE
chmog 666 uucp root $TFILE
uuq -s -P $1 $TFILE

#
# Execute Remote System Clock Synchronization Daemon
uux -z $1!$DAEMON

sleep $ADVANCE_SECS

# Remove the local time file
rm $TFILE

exit 0
-------------------------------------------------------------------------
/* etime.c
 *
 *
 */
#include 
#include 

long time();

int main( argc, argv )
int argc;
char *argv[];
{
	long et, at;

	if( argc != 2 )    {
		fprintf( stderr, "%s: missing argument.\n", argv[ 0 ] );
		exit( 1 );
	}
	if( sscanf( argv[ 1 ], "%ld", &at ) != 1 )    {
		fprintf( stderr, "%s: can't read numerical argument.\n", argv[ 0 ] );
		exit( 1 );
	}

	et = time( (long *)0 );
	printf( "%ld", (et + at) );

	exit( 0 );
	return( 0 );

} /* End main() */

------------------------------------------------------------------------

/* ssyndemon.c
 *
 * A daemon that periodically looks for arriving file that contains
 * the setting for the system clock.
 * The demon only needs to be active when such an activity is scheduled.
 * The remote system might be able to activate the demon before putting
 * the file in place.  Once the demon sets the clock, he should exit until
 * invoked once again.
 *
 * Wakes up every minute.
 *
 */
#include 
#include 
#include 
#include 
#include 

#define TIMEFILE "/usr/tmp/ssyndf"
#define CYCLE 5

int main( argc, argv )
int argc;
char *argv[];
{
	int stime();

	FILE *fptr;
	long elapsed;

	if( signal( SIGINT, SIG_IGN ) != SIG_IGN )
		signal( SIGINT, SIG_IGN );
	if( signal( SIGKILL, SIG_IGN ) != SIG_IGN )
		signal( SIGKILL, SIG_IGN );

	if( fork() == 0 )    {
		/* Fork a child process, sending the daemon into the
		 * loop background.
		 */

		fclose( stdin );
		fclose( stdout );

		while( 1 )    {

			/* Check for the existence of the time file
			 */
			if( access( TIMEFILE, 0 ) == 0 )    {
				fptr = fopen( TIMEFILE, "r" );
				fscanf( fptr, "%ld", &elapsed );
				if( unlink( TIMEFILE ) < 0 )    {
					fprintf( stderr, "%s: can't unlink %s\n", argv[0], TIMEFILE );
					exit( 1 );
				}
				if( stime( &elapsed ) < 0 )    {
					fprintf( stderr, "%s: can't set system time\n", argv[0] );
					exit( 1 );
				}
				exit( 0 );
			}

			/* Otherwise continue waiting */
			 
			/* Wake up and look every CYCLE */
			sleep( CYCLE );
		}
	}
	else    {

		/* Exit parent process */
		if( signal( SIGINT, SIG_DFL ) != SIG_DFL )
			signal( SIGINT, SIG_DFL );
		if( signal( SIGKILL, SIG_DFL ) != SIG_DFL )
			signal( SIGKILL, SIG_DFL );
		exit( 0 );

	} /* End if( fork() ) */

	exit( 0 );

	return( 0 );

} /* End main() */