at.1

<B>Digital的Unix操作系统VAX 4.2源码</B>

.\" SCCSID: @(#)at.1	8.2	3/28/91
.TH at 1
.SH Name
at, batch \- execute commands at a later time
.SH Syntax
.B at
\fItime\fR [\|\fIday\fR\|] [\|\fIfile\fR\|]
.br
.B at
\fB\-r \fIjob...
.br
.B at \-l
[\|\fIjob...\fR\|]
.sp
.br
.B batch
[\|\fIfile\fR\|]
.SH Description
.NXR "at command"
.NXR "command" "executing later"
.NXR "program" "executing later"
The
.PN at
and
.PN batch
commands
use a copy of the named
.I file
(standard input default)
as input to
.MS sh 1
or
.MS csh 1 
at a later time.
A
.PN cd
command to the current directory is inserted
at the beginning,
followed by assignments to all environment variables.
When the script is run, it uses the user and group ID
of the creator of the copy file.
.PP
The 
.PN at
command allows the user to specify when the commands should be executed,
while jobs queued with
.PN batch 
execute when the load level of the system permits.
.PP
The environment variables,
current directory,
.PN umask ,
and
.PN ulimit
are retained when the commands are executed.
However, open files, traps, and priority are lost.
.PP
Users are permitted to use the
.PN at
and
.PN batch
commands if their name appears in the file
.PN /usr/lib/cron/at.allow .
If that file does not exist, the file
.PN /usr/lib/cron/at.deny
is checked to determine if the user should be denied access to
.PN at
and
.PN batch .
If neither file exists, only the superuser is allowed to submit a job.
If only the
.PN at.deny
file exists and is empty, global usage is permitted.
The 
.PN allow/deny
files consist of one user name per line.
.PP
The
.I time
is 1 to 4 digits.  It can, but does not have to be, followed by
A, P, N or M which stand for
AM, PM, noon or midnight, respectively. The A, P, N, and M 
suffixes are case-insensitive.
One and two digit numbers are interpreted as hours, three and
four digits to be hours and minutes. If three digits 
are specified, the first
digit is interpreted to be an hour in the
range 0-9, and the second and third digits as minutes.
If no letters follow the digits, a 24 hour clock time is presumed.
.PP
In addition to 1-4 digits, and suffixes A, P, M, N, you 
can also specify:
.EX 10
at hh:mm
at h:mm
at ham
at hpm
at noon
at midnight
.EE
.PP
The optional
.I day
is either
a month name followed by a day number
or by a day of the week.  If the word week follows, the
.PN at
or
.PN batch 
command is invoked in seven days.
Both commands also recognize standard abbreviations for the
days of the week and months of the year.
The following are examples of legitimate commands:
.EX 10
at 8am jan 24
.sp
at 1530 fr week
.EE
.PP
The
.PN at
programs are executed by periodic execution
of the command 
.PN /usr/lib/atrun
from 
.MS cron 8 .
The granularity of
.PN at
depends upon how often
.I atrun
is executed.
The 
.PN cron
command examines the 
.PN crontab
file every minute.  The 
.PN crontab
file determines when 
.PN /usr/lib/atrun 
is executed.  The default
is every 15 minutes on the 1/4 hour. Editing 
.PN /etc/crontab
makes 
.PN /usr/lib/atrun
run more or less frequently.
.PP
Standard output or error output is lost unless it is redirected.
.PP
The 
.PN at
and
.PN batch
commands 
write the job number to standard error.
.SH Options
.TP 20
.B \-r
Removes jobs previously scheduled by
.PN at
or
.PN batch .
The number is the number reported at invocation by
.PN at
or 
.PN batch .
Only the superuser is allowed to remove another user's jobs.
.TP
.B \-l
Lists all job numbers for all jobs submitted by the user issuing the
.PN at
command.  Even if the user is "root", only numbers for jobs submitted by "root"
are displayed.  To see the numbers of all jobs submitted, enter the
following command:
.EX
% ls -l /usr/spool/at
.EE
.SH Restrictions
.NXR "at command" "restricted"
Due to the granularity of the execution of 
.PN /usr/lib/atrun ,
there may be bugs in scheduling jobs almost
exactly 24 hours into the future.
.SH Diagnostics
Complains about various syntax errors and times that are
out of range.
.SH Files
.ta 2i
/usr/lib/atrun	executor run by cron(8)
.sp
in /usr/spool/at:
.ta .5i 2i
.br
\&	yy.ddd.hhhh.*	activity for year yy, day dd, hour hhhh.
.br
\&	lasttimedone	last \fIhhhh\fR
.br
\&	past	activities in progress
.br
/usr/spool/at/at.allow	list of allowed users	
.br
/usr/spool/at/at.deny	list of denied users
.br
/usr/spool/at	spool directory
.br
/usr/lib/cron	XOPEN compatibility
.SH See Also
crontab(5), cron(8)