at allows some moderately complex time specifications. It accepts times of the form HHMM or HH:MM to run a job at a specific time of day. (If that time is already past, the next day is assumed.) You may also specify `midnight', `noon', or `teatime' (4pm) and you can have a time-of-day suffixed with `AM' or `PM' for running in the morning or the evening. You can also say what day the job will be run, by giving a date in the form month-name day with an optional year, or giving a date of the form MMDDYY or MM/DD/YY or DD.MM.YY. The specification of a date must follow the specification of the time of day. You can also give times like [now] or [now] `+ count time-units', where the time-units can be `minutes', `hours', `days', `weeks,' `months,' or `years' and you can tell at to run the job today by suffixing the time with `today' and to run the job tomorrow by suffixing the time with `tomorrow'.
For example, to run a job at 4pm three days from now, you would do
at
4pm
+
3
days
,
to run a job at 10:00am on July 31, you would do
at
10am
Jul
31
and to run a job at 1am tomorrow, you would do
at
1am
tomorrow
.
Alternatively the time may be specified in a language-neutral fashion by using the -t options.
For both
at
and
batch,
commands are read from standard input or the file specified
with the
-f
option and executed.
The working directory, the environment (except for the variables
TERM
,
TERMCAP
,
DISPLAY
and
_
)
and the
umask
are retained from the time of invocation.
An
at
or
batch
command invoked from a
su(1)
shell will retain the current userid.
The user will be mailed standard error and standard output from his
commands, if any.
Mail will be sent using the command
sendmail(8).
If
at
is executed from a
su(1)
shell, the owner of the login shell will receive the mail.
The superuser may use these commands in any case.
For other users, permission to use at is determined by the files
/var/at/at.allow
and
/var/at/at.deny
.
If the file
/var/at/at.allow
exists, only usernames mentioned in it are allowed to use
.
If
/var/at/at.allow
does not exist,
/var/at/at.deny
is checked, every username not mentioned in it is then allowed
to use
.
If neither exists, only the superuser is allowed use of .
An empty
/var/at/at.deny
means that every user is allowed use these commands.
This is the default configuration.
/var/at/jobs
/var/at/spool
/var/run/utmp
/var/at/at.allow
/var/at/at.deny
/var/at/.lockfile
/var/run/utmp
is not available or corrupted, or if the user is not logged on at the
time
at
is invoked, the mail is sent to the userid found
in the environment variable
LOGNAME
.
If that is undefined or empty, the current userid is assumed.
at and batch as presently implemented are not suitable when users are competing for resources. If this is the case for your site, you might want to consider another batch system, such as nqs.