freebsd-skq/sbin/adjkerntz/adjkerntz.8

.\" Copyright (C) 1993 by Andrew A. Chernov, Moscow, Russia.
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.Dd December 15, 1993
.Dt ADJKERNTZ 8
.Os FreeBSD
.Sh NAME
.Nm adjkerntz
.Nd "adjusts the kernel time if the machine runs wall CMOS clock"
.Sh SYNOPSIS
.Nm adjkerntz
.Fl i
.Nm adjkerntz
.Fl a
.Sh DESCRIPTION
.Nm Adjkerntz
fixes kernel time (makes it UTC) using the current wall CMOS clock value,
the current time zone rule and the kernel timezone value. The adjustment is
enabled only if the file
.Pa /etc/wall_cmos_clock
exists, in other cases it is assumed that the machine runs UTC CMOS clock and
.Nm adjkerntz
does nothing.
.Pp
The adjustment is needed at boot stage and when a time zone
change occurs, so
.Nm adjkerntz
can be called in two forms:
.Bl -tag -width 4n
.It Cm Fl i
initialization call from
.Pa /etc/rc
(before any daemons are started).
.Nm Adjkerntz
makes the first adjustment and the initial time zone offset is stored into
.Pa adjkerntz
kernel variable
for following subsequent
.Nm adjkerntz
calls.
.It Cm Fl a
This form is needed, when time zone changes occur.
.Nm Adjkerntz
uses the previously stored
time zone offset and the changed time zone rule to
produce the new time zone offset, fix the RTC clock and store the new
offset into
.Pa adjkerntz
kernel variable
too.
It is recommended to use this form in root's
.Xr crontab 5
every half of a hour from 0am to 4am
since this times matches most modern time zone changes.
.Pp
.Nm Adjkerntz
clears the kernel timezone structure and makes kernel always run at UTC
time zone.
Super-user privilege is required for all operations.
.Sh ENVIRONMENT
.Bl -tag -width Fl
.It Ev TZ
Time zone change rule, see
.Xr tzset 3 ;
not needed when
.Xr /usr/sbin/tzsetup
or
.Xr zic 8
is used.
.Sh FILES
.Bl -tag -width /etc/wall_cmos_clock -compact
.It Pa /etc/localtime
Current zoneinfo file, see
.Xr /usr/sbin/tzsetup
and
.Xr zic 8 .
.It Pa /etc/wall_cmos_clock
Empty file.
Presence of it indicates that the machine runs wall CMOS clock,
absence indicates UTC CMOS clock.
.Sh SEE ALSO
.Xr tzset 3 ,
.Xr zic 8 ,
.Xr rc 8 ,
.Xr crontab 5 ,
.Xr sysctl 8 ,
.Xr /usr/sbin/tzsetup
.Sh DIAGNOSTICS
No diagnostics.
If any error occurs, an error message printed via
.Xr syslog 3
and
.Nm adjkerntz
exits with return code greater than zero.
.Sh AUTHOR
Andrew A. Chernov <ache@astral.msk.su>
.Sh HISTORY
The
.Nm adjkerntz
command appeared in FreeBSD 1.0.1