rtc(1M) System Administration Commands rtc(1M)NAME
rtc - provide all real-time clock and GMT-lag management
SYNOPSIS
/usr/sbin/rtc [-c] [-z zone-name]
DESCRIPTION
On x86 systems, the rtc command reconciles the difference in the way that time is established between UNIX and MS-DOS systems. UNIX systems
utilize Greenwich Mean Time (GMT), while MS-DOS systems utilize local time.
Without arguments, rtc displays the currently configured time zone string. The currently configured time zone string is based on what was
last recorded by rtc-z zone-name.
The rtc command is not normally run from a shell prompt; it is generally invoked by the system. Commands such as date(1) and rdate(1M),
which are used to set the time on a system, invoke /usr/sbin/rtc -c to ensure that daylight savings time (DST) is corrected for properly.
OPTIONS -c This option checks for DST and makes corrections if necessary. It is normally run once a day by a cron job.
If there is no RTC time zone or /etc/rtc_config file, this option will do nothing.
-z zone-name This option, which is normally run by the system at software installation time, is used to specify the time zone in which
the RTC is to be maintained. It updates the configuration file /etc/rtc_config with the name of the specified zone and the
current GMT lag for that zone. If there is an existing rtc_config file, this command will update it. If not, this command
will create it.
FILES
/etc/rtc_config The data file used to record the time zone and GMT lag. This file is completely managed by /usr/sbin/rtc, and it is
read by the kernel.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Architecture |x86 |
+-----------------------------+-----------------------------+
|Availability |SUNWcsu |
+-----------------------------+-----------------------------+
SEE ALSO date(1), rdate(1M), attributes(5)SunOS 5.10 3 Oct 2003 rtc(1M)
Check Out this Related Man Page
CTIME(3) Library Functions Manual CTIME(3)NAME
ctime, localtime, gmtime, asctime, timezone, tzset - convert date and time to ASCII
SYNOPSIS
void tzset()
char *ctime(clock)
time_t *clock;
#include <time.h>
char *asctime(tm)
struct tm *tm;
struct tm *localtime(clock)
time_t *clock;
struct tm *gmtime(clock)
time_t *clock;
char *timezone(zone, dst)
DESCRIPTION
Tzset uses the value of the environment variable TZ to set up the time conversion information used by localtime.
If TZ does not appear in the environment, the TZDEFAULT file (as defined in tzfile.h) is used by localtime. If this file fails for any
reason, the GMT offset as provided by the kernel is used. In this case, DST is ignored, resulting in the time being incorrect by some
amount if DST is currently in effect. If this fails for any reason, GMT is used.
If TZ appears in the environment but its value is a null string, Greenwich Mean Time is used; if TZ appears and begins with a slash, it is
used as the absolute pathname of the tzfile(5)-format file from which to read the time conversion information; if TZ appears and begins
with a character other than a slash, it's used as a pathname relative to the system time conversion information directory, defined as TZDIR
in the include file tzfile.h. If this file fails for any reason, GMT is used.
Programs that always wish to use local wall clock time should explicitly remove the environmental variable TZ with unsetenv(3).
Ctime converts a long integer, pointed to by clock, such as returned by time(2) into ASCII and returns a pointer to a 26-character string
in the following form. All the fields have constant width.
Sun Sep 16 01:03:52 1973
Localtime and gmtime return pointers to structures containing the broken-down time. Localtime corrects for the time zone and possible day-
light savings time; gmtime converts directly to GMT, which is the time UNIX uses. Asctime converts a broken-down time to ASCII and returns
a pointer to a 26-character string.
The structure declaration from the include file is:
struct tm {
int tm_sec; /* 0-59 seconds */
int tm_min; /* 0-59 minutes */
int tm_hour; /* 0-23 hour */
int tm_mday; /* 1-31 day of month */
int tm_mon; /* 0-11 month */
int tm_year; /* 0- year - 1900 */
int tm_wday; /* 0-6 day of week (Sunday = 0) */
int tm_yday; /* 0-365 day of year */
int tm_isdst; /* flag: daylight savings time in effect */
char **tm_zone; /* abbreviation of timezone name */
long tm_gmtoff; /* offset from GMT in seconds */
};
Tm_isdst is non-zero if a time zone adjustment such as Daylight Savings time is in effect.
Tm_gmtoff is the offset (in seconds) of the time represented from GMT, with positive values indicating East of Greenwich.
Timezone remains for compatibility reasons only; it's impossible to reliably map timezone's arguments (zone, a "minutes west of GMT" value
and dst, a "daylight saving time in effect" flag) to a time zone abbreviation.
If the environmental string TZNAME exists, timezone returns its value, unless it consists of two comma separated strings, in which case the
second string is returned if dst is non-zero, else the first string. If TZNAME doesn't exist, zone is checked for equality with a built-in
table of values, in which case timezone returns the time zone or daylight time zone abbreviation associated with that value. If the
requested zone does not appear in the table, the difference from GMT is returned; e.g. in Afghanistan, timezone(-(60*4+30), 0) is appropri-
ate because it is 4:30 ahead of GMT, and the string GMT+4:30 is returned. Programs that in the past used the timezone function should
return the zone name as set by localtime to assure correctness.
FILES
/usr/share/zoneinfotime zone information directory
/etc/localtime local time zone file
SEE ALSO gettimeofday(2), getenv(3), time(3), tzfile(5), environ(7)NOTE
The return values point to static data whose content is overwritten by each call. The tm_zone field of a returned struct tm points to a
static array of characters, which will also be overwritten at the next call (and by calls to tzset).
4th Berkeley Distribution November 27, 1996 CTIME(3)