date.1

早期freebsd实现

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.\"     @(#)date.1	8.2 (Berkeley) 11/17/93
.\"
.Dd November 17, 1993
.Dt DATE 1
.Os
.Sh NAME
.Nm date
.Nd display or set date and time
.Sh SYNOPSIS
.Nm date
.Op Fl d Ar dst
.Op Fl r Ar seconds
.Op Fl t Ar minutes_west
.Op Fl nu
.Op Cm + Ns Ar format
.Op [yy[mm[dd[hh]]]]mm[\&.ss]
.Sh DESCRIPTION
.Nm Date
displays the current date and time when invoked without arguments.
Providing arguments will format the date and time in a user-defined
way or set the date.
Only the superuser may set the date.
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl d
Set the kernel's value for daylight savings time.
If
.Ar dst
is non-zero, future calls
to
.Xr gettimeofday 2
will return a non-zero
.Ql tz_dsttime  .
.It Fl n
The utility
.Xr timed 8
is used to synchronize the clocks on groups of machines.
By default, if
.Xr timed
is running,
.Nm date
will set the time on all of the machines in the local group.
The
.Fl n
option stops
.Nm date
from setting the time for other than the current machine.
.It Fl r
Print out the date and time in
.Ar seconds
from the Epoch.
.It Fl t
Set the kernel's value for minutes west of
.Tn GMT .
.Ar Minutes_west
specifies the number of minutes returned in
.Ql tz_minuteswest  
by future calls to
.Xr gettimeofday 2 .
.It Fl u
Display or set the date in
.Tn UCT
(universal) time.
.El
.Pp
An operand with a leading plus (``+'') sign signals a user-defined format
string which specifies the format in which to display the date and time.
The format string may contain any of the conversion specifications described
in the 
.Xr strftime 3
manual page, as well as any arbitrary text.
The format string for the default display is:
.Bd -literal -offset indent
``%a %b %e %H:%M:%S %Z n''.
.Ed
.Pp
If an operand does not have a leading plus sign, it is interpreted as
a value for setting the system's notion of the current date and time.
The canonical representation for setting the date and time is:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar yy
Year in abbreviated form (.e.g 89 for 1989).
.It Ar mm
Numeric month.
A number from 1 to 12.
.It Ar dd
Day, a number from 1 to 31.
.It Ar hh
Hour, a number from 0 to 23.
.It Ar mm
Minutes, a number from 0 to 59.
.It Ar .ss
Seconds, a number from 0 to 61 (59 plus a a maximum of two leap seconds).
.El
.Pp
Everything but the minutes is optional.
.Pp
Time changes for Daylight Saving and Standard time and leap seconds
and years are handled automatically.
.Sh EXAMPLES
The command:
.Bd -literal -offset indent
date ``+DATE: %m/%d/%y%nTIME: %H:%M:0n''
.Ed
.Pp
will display:
.Bd -literal -offset indent
DATE: 11/21/87
TIME: 13:36:16
.Ed
.Pp
The command:
.Bd -literal -offset indent
date 8506131627
.Ed
.Pp
sets the date to
.Dq Li "June 13, 1985, 4:27 PM" .
.Pp
The command:
.Bd -literal -offset indent
date 1432
.Ed
.Pp
sets the time to
.Li "2:32 PM" ,
without modifying the date.
.Sh ENVIRONMENTAL VARIABLES
The following environment variables affect the execution of
.Nm date :
.Bl -tag -width TZ
.It Ev TZ
The timezone to use when displaying dates.
See
.Xr environ 7
for more information.
.El
.Sh FILES
.Bl -tag -width /var/log/messages -compact
.It Pa /var/log/wtmp
A record of date resets and time changes.
.It Pa /var/log/messages
A record of the user setting the time.
.El
.Sh SEE ALSO
.Xr gettimeofday 2 ,
.Xr strftime 3 ,
.Xr utmp 5 ,
.Xr timed 8
.Rs
.%T "TSP: The Time Synchronization Protocol for UNIX 4.3BSD"
.%A R. Gusella
.%A S. Zatti
.Re
.Sh DIAGNOSTICS
Exit status is 0 on success, 1 if unable to set the date, and 2
if able to set the local date, but unable to set it globally.
.Pp
Occasionally, when
.Xr timed
synchronizes the time on many hosts, the setting of a new time value may
require more than a few seconds.
On these occasions,
.Nm date
prints:
.Ql Network time being set .
The message
.Ql Communication error with timed
occurs when the communication
between
.Nm date
and
.Xr timed
fails.
.Sh BUGS
The system attempts to keep the date in a format closely compatible
with
.Tn VMS .
.Tn VMS ,
however, uses local time (rather than
.Tn GMT )
and does not understand daylight-savings time.
Thus, if you use both
.Tn UNIX
and
.Tn VMS ,
.Tn VMS
will be running on
.Tn GMT .
.Sh STANDARDS
The
.Nm date
command is expected to be compatible with
.St -p1003.2 .