1 RTC(1M) Maintenance Commands RTC(1M)
2
3
4
5 NAME
6 rtc - provide all real-time clock and GMT-lag management
7
8 SYNOPSIS
9 /usr/sbin/rtc [-c] [-z zone-name]
10
11
12 DESCRIPTION
13 On x86 systems, the rtc command reconciles the difference in the way
14 that time is established between UNIX and MS-DOS systems. UNIX systems
15 utilize Greenwich Mean Time (GMT), while MS-DOS systems utilize local
16 time.
17
18
19 Without arguments, rtc displays the currently configured time zone
20 string. The currently configured time zone string is based on what was
21 last recorded by rtc-z zone-name.
22
23
24 The rtc command is not normally run from a shell prompt; it is
25 generally invoked by the system. Commands such as date(1) and
26 rdate(1M), which are used to set the time on a system, invoke
27 /usr/sbin/rtc -c to ensure that daylight savings time (DST) is
28 corrected for properly.
29
30 OPTIONS
31 -c
32 This option checks for DST and makes corrections if
33 necessary. It is normally run once a day by a cron job.
34
35 If there is no RTC time zone or /etc/rtc_config file,
36 this option will do nothing.
37
38
39 -z zone-name
40 This option, which is normally run by the system at
41 software installation time, is used to specify the time
42 zone in which the RTC is to be maintained. It updates
43 the configuration file /etc/rtc_config with the name of
44 the specified zone and the current GMT lag for that
45 zone. If there is an existing rtc_config file, this
46 command will update it. If not, this command will
47 create it.
48
49
50 FILES
51 /etc/rtc_config
52 The data file used to record the time zone and GMT
53 lag. This file is completely managed by
54 /usr/sbin/rtc, and it is read by the kernel.
55
56
57 ATTRIBUTES
58 See attributes(5) for descriptions of the following attributes:
59
60
61
62
63 +---------------+-----------------+
64 |ATTRIBUTE TYPE | ATTRIBUTE VALUE |
65 +---------------+-----------------+
66 |Architecture | x86 |
67 +---------------+-----------------+
68
69 SEE ALSO
70 date(1), rdate(1M), attributes(5)
71
72
73
74 October 3, 2003 RTC(1M)
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1 RTC(1M) Maintenance Commands RTC(1M)
2
3 NAME
4 rtc - provide all real-time clock and UTC-lag management
5
6 SYNOPSIS
7 rtc [-csuvw] [-z zone-name]
8
9 DESCRIPTION
10 The Real Time Clock (RTC) is the hardware device on x86 computers that
11 maintains the date and time. The RTC is battery-powered, so that it
12 keeps running when the computer is shut down. It can be set from the
13 BIOS and also from the operating system running on the computer. The RTC
14 has no setting for the time zone or for Daylight Saving Time (DST). It
15 relies on the operating system for these facilities and for automatic
16 changes between standard time and DST.
17
18 On x86 systems, the rtc command reconciles the difference in the way that
19 time is established between UNIX and Windows systems. The internal clock
20 on UNIX systems utilizes Universal Coordinated Time (UTC) while Windows
21 systems usually expect the RTC to run in local time, including DST
22 changes.
23
24 Without arguments, rtc displays the currently configured time zone string
25 for the RTC. The currently configured time zone string is based on what
26 was last recorded by rtc -z zone-name.
27
28 The rtc command is not normally run from a shell prompt; it is generally
29 invoked by the system. Commands such as date(1) and rdate(1M), which are
30 used to set the time on a system, invoke rtc -c to ensure that daylight
31 savings time (DST) is corrected for properly.
32
33 OPTIONS
34 -c This option checks for DST and makes corrections to the RTC if
35 necessary. It is normally run once a day by a cron(1M) job.
36
37 If there is no RTC time zone or /etc/rtc_config file, this option
38 will do nothing.
39
40 -s This option specifies that the RTC runs in local standard time
41 all year round. It is incompatible with Windows, but is
42 convenient if only one operating system is to be run on the
43 computer. The cron(1M) command is not necessary, and should not
44 be run.
45
46 -u This option specifies that the RTC runs in UTC time. As a side
47 effect, it sets the time zone in /etc/rtc_config to UTC. Windows
48 can operate in UTC time, but requires a registry change to do so.
49 The cron(1M) command is not necessary.
50
51 -v This option specifies that the RTC tracks local time, including
52 DST changes. This is the default. It accomodates Windows with
53 no changes. The cron(1M) command is necessary to change the RTC
54 when DST is in effect.
55
56 -w This option does nothing. It is present for compatibility with
57 Solaris 11.
58
59 -z zone-name
60 This option, which is normally run by the system at software
61 installation time, is used to specify the time zone in which the
62 RTC is to be maintained. It updates the configuration file
63 /etc/rtc_config with the name of the specified zone and the
64 current UTC lag for that zone. If there is an existing
65 /etc/rtc_config file, this command will update it. If not, this
66 command will create it.
67
68 FILES
69 /etc/rtc_config The data file used to record the time zone and UTC lag.
70 This file is completely managed by rtc. At boot time,
71 the kernel reads the UTC lag from this file, and uses it
72 to set the system time.
73
74 ARCHITECTURE
75 x86
76
77 SEE ALSO
78 date(1), cron(1M), rdate(1M), attributes(5)
79
80 illumos January 31, 2018 illumos
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