adjkerntz(8)

NAME

adjkerntz - adjust local time CMOS clock to reflect time

zone changes and
keep current timezone offset for the kernel

SYNOPSIS

adjkerntz -i
adjkerntz -a [-s]

DESCRIPTION

The adjkerntz utility maintains the proper relationship be

tween the kernel clock, which is always set to UTC, and the CMOS clock,

which may be
set to local time. The adjkerntz utility also informs the

kernel about
machine timezone shifts to maintain proper timestamps for

local time file
systems such as the MS-DOS file system. The main purpose of

this thing
is not general fixing of initially broken MS-DOS file times

tamp idea but
keeping the same timestamps between FreeBSD MS-DOS file sys

tem and MS-DOS
operating system installed on the same machine. If the file
/etc/wall_cmos_clock exists, it means that CMOS clock keeps

local time
(MS-DOS and MS-Windows compatible mode). If that file does

not exist, it
means that the CMOS clock keeps UTC time. The adjkerntz

utility passes
this state to the machdep.wall_cmos_clock kernel variable.

Adjustments may be needed at system startup and shutdown,

and whenever a
time zone change occurs. To handle these different situa

tions, adjkerntz
is invoked in two ways:

-i This form handles system startups and shutdowns. The

adjkerntz

utility is invoked with this option from /etc/rc on

entry to multiuser mode, before any other daemons have been started.

The
adjkerntz utility puts itself into the background.

Then, for a
local time CMOS clock, adjkerntz reads the local time

from it and
sets the kernel clock to the corresponding UTC time.

The adjkerntz
utility also stores the local time zone offset into

the
machdep.adjkerntz kernel variable, for use by subse

quent invocations of 'adjkerntz -a' and by local time file sys

tems.

For a local time CMOS clock 'adjkerntz -i' pauses, and

remains
inactive as a background daemon until it receives a

SIGTERM. The
SIGTERM will normally be sent by init(8) when the sys

tem leaves
multi-user mode (usually, because the system is being

shut down).
After receiving the SIGTERM, adjkerntz reads the UTC

kernel clock
and updates the CMOS clock, if necessary, to ensure

that it
reflects the current local time zone. Then adjkerntz

exits.

-a [-s]

This form is used to update the local time CMOS clock

and kernel
machdep.adjkerntz variable when time zone changes oc

cur, e.g., when
entering or leaving daylight savings time. The

adjkerntz utility
uses the kernel clock's UTC time, the previously

stored time zone
offset, and the changed time zone rule to calculate a

new time zone
offset. It stores the new offset into the

machdep.adjkerntz kernel
variable, and updates the wall CMOS clock to the new

local time.
If 'adjkerntz -a' was started at a nonexistent time

(during a timezone change), it exits with a warning diagnostic un

less the -s
option was used, in which case adjkerntz sleeps 30

minutes and
tries again.

This form should be invoked from root's crontab(5) ev

ery half hour
between midnight and 5am, when most modern time zone

changes occur.
Warning: do not use the -s option in a crontab(5) com

mand line, or
multiple 'adjkerntz -a' instances could conflict with

each other.

The adjkerntz utility clears the kernel timezone structure

and makes the
kernel clock run in the UTC time zone. Super-user privi

leges are
required for all operations.

ENVIRONMENT

TZ Time zone change rule, see tzset(3); not needed

when

tzsetup(8) or zic(8) is used.

FILES

/etc/localtime Current zoneinfo file, see tzsetup(8)

and zic(8).
/etc/wall_cmos_clock Empty file. Its presence indicates

that the

machine's CMOS clock is set to local

time, while
its absence indicates a UTC CMOS

clock.

DIAGNOSTICS

No diagnostics. If an error occurs, adjkerntz logs an error

message via
syslog(3) and exits with a nonzero return code.

SEE ALSO

tzset(3), crontab(5), mount_msdosfs(8), rc(8), sysctl(8),

tzsetup(8),
zic(8)

HISTORY

The adjkerntz utility appeared in FreeBSD 1.0.

AUTHORS

Andrey A. Chernov <ache@astral.msk.su>

BSD April 4, 1996

BSD