1 .\" Copyright (C) 1993-1998 by Andrey A. Chernov, Moscow, Russia.
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32 .Nd "adjust local time CMOS clock to reflect time zone changes and keep current timezone offset for the kernel"
41 utility maintains the proper relationship between the kernel clock, which
42 is always set to UTC, and the CMOS clock, which may be set to local
46 utility also informs the kernel about machine timezone shifts to
47 maintain proper timestamps for local time file systems such as the MS-DOS
49 The main purpose of this thing is not general fixing of
50 initially broken MS-DOS file timestamp idea but keeping
51 the same timestamps between
54 and MS-DOS operating system installed on the same
57 .Pa /etc/wall_cmos_clock
58 exists, it means that CMOS clock keeps local time (MS-DOS and MS-Windows
60 If that file does not exist, it means that the CMOS clock keeps UTC time.
63 utility passes this state to the
64 .Pa machdep.wall_cmos_clock
67 Adjustments may be needed at system startup and shutdown, and
68 whenever a time zone change occurs.
69 To handle these different situations,
71 is invoked in two ways:
74 This form handles system startups and shutdowns.
77 utility is invoked with this option from
79 on entry to multi-user mode, before any other daemons have been started.
82 utility puts itself into the background.
83 Then, for a local time CMOS clock,
85 reads the local time from it
86 and sets the kernel clock to the corresponding UTC time.
89 utility also stores the local time zone offset into the
91 kernel variable, for use by subsequent invocations of
93 and by local time file systems.
95 For a local time CMOS clock
97 pauses, and remains inactive as a background daemon until it
99 The SIGTERM will normally be sent by
101 when the system leaves multi-user mode (usually, because the system
103 After receiving the SIGTERM,
105 reads the UTC kernel clock and updates the CMOS clock, if necessary,
106 to ensure that it reflects the current local time zone.
111 This form is used to update the local time CMOS clock and kernel
112 .Pa machdep.adjkerntz
113 variable when time zone changes occur,
114 e.g., when entering or leaving daylight savings time.
117 utility uses the kernel clock's UTC time,
118 the previously stored
119 time zone offset, and the changed time zone rule to
120 calculate a new time zone offset.
121 It stores the new offset into the
122 .Pa machdep.adjkerntz
123 kernel variable, and updates the wall CMOS clock to the new local time.
126 was started at a nonexistent time (during a timezone change), it exits
127 with a warning diagnostic unless the
129 option was used, in which case
131 sleeps 30 minutes and tries again.
133 This form should be invoked from root's
135 every half hour between midnight and 5am, when most modern time
137 Warning: do not use the
141 command line, or multiple
143 instances could conflict with each other.
148 utility clears the kernel timezone structure and makes the kernel clock run
149 in the UTC time zone.
150 Super-user privileges are required for all operations.
154 Time zone change rule, see
163 .Bl -tag -width /etc/wall_cmos_clock -compact
164 .It Pa /etc/localtime
165 Current zoneinfo file, see
169 .It Pa /etc/wall_cmos_clock
171 Its presence indicates that the machine's CMOS clock is set to local
172 time, while its absence indicates a UTC CMOS clock.
178 logs an error message via
180 and exits with a nonzero return code.
184 .Xr mount_msdosfs 8 ,
195 .An Andrey A. Chernov Aq ache@astral.msk.su