path: root/usr.bin/at/at.1

.\" $OpenBSD: at.1,v 1.59 2024/11/05 16:21:13 sobrado Exp $
.\"
.\" Copyright (C) 1993, 1994  Thomas Koenig
.\" Copyright (C) 1993  David Parsons
.\" Copyright (C) 2002  Todd C. Miller
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. The name of the author(s) may not be used to endorse or promote
.\"    products derived from this software without specific prior written
.\"    permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS OR
.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
.\" IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT, INDIRECT,
.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd $Mdocdate: November 5 2024 $
.Dt AT 1
.Os
.Sh NAME
.Nm at ,
.Nm batch
.Nd queue, examine or delete jobs for later execution
.Sh SYNOPSIS
.Nm at
.Op Fl bm
.Op Fl f Ar file
.Op Fl l Op Ar job ...
.Op Fl q Ar queue
.Fl t Ar time_arg | timespec
.Nm at
.Fl c | r
.Ar job ...
.Nm batch
.Op Fl m
.Op Fl f Ar file
.Op Fl q Ar queue
.Op Ar timespec
.Sh DESCRIPTION
.Nm at
and
.Nm batch
read commands from standard input or a specified file which
are to be executed at a later time, via the user's shell as
specified by the
.Ev SHELL
environment variable.
If
.Ev SHELL
is not set, the shell in the user's password database entry is used
instead.
If all else fails,
.Xr sh 1
will be used.
.Pp
The related programs are as follows:
.Bl -tag -width Ds
.It Nm at
Executes commands at a specified time.
.It Nm batch
Executes commands when system load levels permit.
In other words, when
the load average drops below 1.5, or the value specified in the invocation of
.Xr cron 8 .
.El
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl b
An alias for
.Nm batch .
.It Fl c Ar job ...
Prints the jobs listed on the command line to standard output.
.It Fl f Ar file
Reads the job from
.Ar file
rather than standard input.
.It Fl l Op Ar job ...
Displays the queue of jobs which are currently awaiting execution.
If a
.Ar job
argument is specified, only the specified jobs will be displayed.
Unless the user is the superuser, only the user's own jobs will be
displayed.
.It Fl m
Send mail to the user when the job has completed, even if there was no
output.
.It Fl q Ar queue
Uses the specified queue.
A queue designation consists of a single letter.
Valid queue designations range from
.Sy a
to
.Sy z
and
.Sy A
to
.Sy Z .
The
.Sy c
queue is the default for
.Nm at
and the
.Sy E
queue for
.Nm batch .
Queues with higher letters run with increased niceness.
If a job is submitted to a queue designated with an uppercase letter, it
is treated as if it had been submitted to batch at that time.
If the user specified the
.Fl l
option and
.Nm at
is given a specific queue, only jobs pending in that queue will be shown.
.It Fl r Ar job ...
Remove the specified job(s) from the
.Nm at
queue.
.It Fl t Ar time_arg
Specify the job time.
The argument should be of the form
.Oo Oo Ar cc Oc Ns Ar yy Oc Ns Ar mmddHHMM Ns Op \&. Ns Ar SS
(matching
.Xr touch 1 Ap s
.Fl t
format),
where the parts of the argument represent the following:
.Pp
.Bl -tag -width Ds -compact -offset indent
.It Ar ccyy
Year.
If yy is specified, but cc is not,
a value for yy between 69 and 99 results in a cc value of 19.
Otherwise, a cc value of 20 is used.
.It Ar mm
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
Minute:
a number from 0 to 59.
.It Ar SS
Second:
a number from 0 to 60
(permitting a leap second),
preceded by a period.
The default is 0.
.El
.It Ar timespec
As well as the
.Fl t
option,
.Nm at
alternatively allows some moderately complex
.Ar timespec
specifications.
It accepts times of the form
.Ar HHMM
or
.Ar HH:MM
to run a job at a specific time of day
(if that time is already past, the next day is assumed).
It is also possible to specify
.Cm midnight ,
.Cm noon ,
.Cm now ,
or
.Cm teatime
(4pm),
or have a time-of-day suffixed with
.Cm AM
or
.Cm PM
for running in the morning or the evening.
To say what day the job will be run,
give a date in the form
.Ar \%month-name day
with an optional
.Ar year ,
or giving a date of the form
.Ar dd.mm.ccyy ,
.Ar dd.mm.yy ,
.Ar mm/dd/ccyy ,
.Ar mm/dd/yy ,
.Ar mmddccyy ,
or
.Ar mmddyy .
.Pp
The year may be given as two or four digits.
If the year is given as two digits, it is taken to occur as soon as
possible in the future, which may be in the next century \(em
unless it's last year, in which case it's considered to be
a typo.
.Pp
The specification of a date must follow the specification of
the time of day.
A time like
.Oo Cm now Oc Cm + Ar count time-units
may be given,
where the time-units can be
.Cm minutes ,
.Cm hours ,
.Cm days ,
.Cm weeks ,
.Cm months ,
or
.Cm years
(the singular forms are also accepted).
To tell
.Nm at
to run the job today or tomorrow,
suffix the time with
.Cm today
or
.Cm tomorrow .
The
.Cm next
keyword may be used as an alias for
.Cm + 1 .
.Pp
For example, to run a job at 4pm three days from now, use
.Ic at 4pm + 3 days .
To run a job at 10:00am on July 31, use
.Ic at 10am Jul 31 .
To run a job at 1am tomorrow, use
.Ic at 1am tomorrow .
To run a job at midnight in one week's time, use
.Ic at midnight next week .
.El
.Pp
For both
.Nm at
and
.Nm batch ,
commands are read from standard input (or the file specified
with the
.Fl f
option) and executed.
The working directory, the environment (except for the variables
.Ev BASH_VERSINFO ,
.Ev DISPLAY ,
.Ev EUID ,
.Ev GROUPS ,
.Ev PPID ,
.Ev SHELLOPTS ,
.Ev SSH_AGENT_PID ,
.Ev SSH_AUTH_SOCK ,
.Ev TERM ,
.Ev TERMCAP ,
.Ev UID ,
and
.Ev _ ) ,
and the
.Ar umask
are retained from the time of invocation.
An
.Nm at
or
.Nm batch
command invoked from a
.Xr su 1
shell will retain the current user ID.
The user will be mailed standard error and standard output from his
commands, if any.
If
.Nm at
is executed from a
.Xr su 1
shell, the owner of the login shell will receive the mail.
.Pp
For non-root users, permission to run
.Nm
is determined by the files
.Pa /var/cron/at.allow
and
.Pa /var/cron/at.deny .
.Em Note :
these files must be readable by group crontab (if they exist).
.Pp
If the file
.Pa /var/cron/at.allow
exists, only usernames mentioned in it are allowed to use
.Nm at .
If
.Pa /var/cron/at.allow
does not exist,
.Pa /var/cron/at.deny
is checked.
Every username not mentioned in it is then allowed to use
.Nm at .
If neither exists, only the superuser is allowed to run
.Nm at .
.Pp
An empty
.Pa /var/cron/at.deny
means that every user is allowed to use these commands.
This is the default configuration.
.Sh FILES
.Bl -tag -width /var/cron/at.allow -compact
.It Pa /var/cron/atjobs
directory containing job files
.It Pa /var/cron/at.allow
allow permission control
.It Pa /var/cron/at.deny
deny permission control
.El
.Sh EXIT STATUS
The
.Nm
utility exits with one of the following values:
.Pp
.Bl -tag -width Ds -offset indent -compact
.It 0
Jobs were successfully submitted, removed, or listed.
.It >0
An error occurred.
.El
.Sh SEE ALSO
.Xr atq 1 ,
.Xr atrm 1 ,
.Xr nice 1 ,
.Xr sh 1 ,
.Xr touch 1 ,
.Xr umask 2 ,
.Xr cron 8
.Sh STANDARDS
The
.Nm
and
.Nm batch
utilities are compliant with the
.St -p1003.1-2024
specification.
.Pp
The
.Nm
flags
.Op Fl bc
and the
.Cm teatime
.Ar timespec
are extensions to that specification.
.Pp
.St -p1003.1-2024
states that
.Nm batch
is equivalent to running
.Qq Cm at -q b -m now .
This implementation permits a
.Ar timespec
argument, as well as the ability to read from a file
.Pq Fl f
and specify a job queue
.Pq Fl q ,
and does not send mail to the user
.Pq Fl m
by default.
.Pp
By default,
.St -p1003.1-2024
schedules
.Nm at
jobs in queue
.Sy a
and
.Nm batch
jobs in queue
.Sy b .
.Pp
The at.allow/deny mechanism is marked by
.St -p1003.1-2024
as being an
X/Open System Interfaces
option.
.Sh AUTHORS
.An -nosplit
.Nm at
was mostly written by
.An Thomas Koenig Aq Mt ig25@rz.uni-karlsruhe.de .
The time parsing routines are by
.An David Parsons Aq Mt orc@pell.chi.il.us .
.Sh BUGS
.Nm at
and
.Nm batch
as presently implemented are not suitable when users are competing for
resources.