at
and
batch
read commands from standard input or a specified file which are to
be executed at a later time, using
/bin/sh .
at
executes commands at a specified time.
atq
lists the user's pending jobs, unless the user is the superuser; in that
case, everybody's jobs are listed.
atrm
batch
executes commands when system load levels permit; in other words, when the load average
drops below 0.8, or the value specified in the invocation of
atrun .
At
allows fairly complex time
specifications, extending the POSIX.2 standard. It accepts times
of the form
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
\+
count
time-units,
where the time-units can be
minutes,
hours,
days,
or
weeks
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.
The exact definition of the time specification can be found in
/usr/doc/at-3.1.7/timespec .
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 ,
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
/usr/sbin/sendmail .
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
/etc/at.allow
and
/etc/at.deny .
If the file
/etc/at.allow
exists, only usernames mentioned in it are allowed to use
at .
If
/etc/at.allow
does not exist,
/etc/at.deny
is checked, every username not mentioned in it is then allowed
to use
at .
If neither exists, only the superuser is allowed use of at.
An empty
/etc/at.deny
means that every user is allowed use these commands, this is the
default configuration.