Manual Pages  — AT

The at utility 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.) As an alternative, the following keywords may be specified: midnight, noon, or teatime (4pm) and time-of-day may be suffixed with AM or PM for running in the morning or the evening. The day on which the job is to be run may also be specified by giving a date in the form  month-name day with an optional year, or giving a date of the forms DD.MM.YYYY, DD.MM.YY, MM/DD/YYYY, MM/DD/YY, MMDDYYYY , or MMDDYY. The specification of a date must follow the specification of the time of day. Time can also be specified as: [ now] + count  time-units, where the time-units can be minutes, hours, days, weeks, months or years and at may be told 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, use at, to run a job at 10:00am on July 31, use at and to run a job at 1am tomorrow, use at.

The at utility also supports the POSIX time format (see -t option).

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 at. In these two files, a user is considered to be listed only if the user name has no blank or other characters before it on its line and a newline character immediately after the name, even at the end of the file. Other lines are ignored and may be used for comments.

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 at.

If neither exists, only the superuser is allowed use of at. This is the default configuration.