at Command

Purpose

Runs commands at a later time.

Syntax

To Schedule Jobs to Run at a Later Time

at [ -c | -k | -s | -q Queue ] [ -m ] [ -f File ] { -t Date |Time [ Day ] [ Increment ] }

To Report Scheduled Jobs

at -l [ -v ] [ -o ] [ Job ... | -q Queue ]

at -n [ User ]

To Remove Scheduled Jobs

at -r [ -F ] [ -i ] Job ...

at -r [ -F ] [ -i ] -u User

Description

The at command reads from standard input the names of commands to be run at a later time and allows you to specify when the commands should be run.

The at command mails you all output from standard output and standard error for the scheduled commands, unless you redirect that output. It also writes the job number and the scheduled time to standard error.

When the at command is executed, it retains the current process environment. It does not retain open file descriptors, traps, and priority.

The /var/adm/cron/at.allow and /var/adm/cron/at.deny files control what users can use the at command. A person with root user authority can create, edit, or delete these files. Entries in these files are user login names with one name to a line. The following is an example of an at.allow file:

root
nick
dee
sarah

If the at.allow file exists, only users whose login names appear in it can use the at command. A system administrator can explicitly stop a user from using the at command by listing the user's login name in the at.deny file. If only the at.deny file exists, any user whose name does not appear in the file can use the at command.

A user cannot use the at command if one of the following is true:

• The at.allow file and the at.deny file do not exist (allows root user only).
• The at.allow file exists but the user's login name is not listed in it.
• The at.deny file exists and the user's login name is listed in it.

If the at.allow file does not exist and the at.deny file does not exist, only users with root authority can submit a job with the at command.

To schedule a job to run at a later time, you must specify a time to start the job. You may specify the time by using either the -t Date flag or the Time, Day, and Increment parameters. At most, 60 jobs can be scheduled in any given run queue at the granularity of one per second. If more jobs than can be handled are submitted, for every job beyond 60, a file _at<pid> is created in /var/spool/cron/atjobs/ which can be safely deleted by the end user.

The Date variable to the -t flag is specified using the following format:

[[CC]YY]MMDDhhmm[.SS]

The digits in the Date variable are defined as follows:

Both the CC and YY digits are optional. If neither is given, the current year is assumed. If the YY digits are specified but the CC digits are not, the CC digits are defined as follows:

• If the value of the YY digits is between 70 and 99, the value of the CC digits is assumed to be 19.
• If the value of the YY digits is between 00 and 37, the value of the CC digits is assumed to be 20.
• The default value of SS is 00.

  For years between 2038 and 2105, specify year in the yyyy format.

The resulting time is affected by the value of the TZ environment variable.

The Time parameter may be specified as a number followed by an optional suffix. The at command interprets one- and two-digit numbers as hours. It interprets four digits as hours and minutes. The T_FMT item in the LC_TIME locale category specifies the order of hours and minutes. The default order is the hour followed by the minute. You can also separate hours and minutes with a : (colon). The default order is Hour:Minute.

In addition, you may specify one of the following suffixes:

• am
• pm
• zulu

If you do not specify am or pm, the at command uses a 24-hour clock. These suffixes can follow the time as a separate argument or separated with spaces. The am and pm suffixes are defined values from the AM_STR and PM_STR items in the LC_TIME locale category. The suffix zulu indicates that the time is GMT (Greenwich Mean Time).

The at command also recognizes the following keywords as special values for the Time parameter:

• noon
• midnight
• now
• A for AM
• P for PM
• N for noon
• M for midnight

You may specify the optional Day parameter as either a month name and a day number (and possibly a year number preceded by a comma), or a day of the week. The D_FMT item in the LC_TIME locale category specifies the order of the month and day (by default, month followed by day). The DAY_1 through DAY_7 items in the LC_TIME locale category specify long day names. The ABDAY_1 through ABDAY_7 items in the LC_TIME locale category specify short day names. The MON_1 through MON_12 items in the LC_TIME locale category specify long month names. The ABMON_1 through ABMON_12 items in the LC_TIME locale category specify short month names. By default, the long name is fully spelled out; the short name is abbreviated to two or more characters for weekdays, and three characters for months.

The at command recognizes today and tomorrow as special default values for the Day parameter. The today value is the default Day if the specified time is later than the current hour; the tomorrow value is the default if the time is earlier than the current hour. If the specified month is less than the current month (and a year is not given), next year is the default year.

Flags

Parameters

• A + (plus sign) followed by a number and one of the following words:
  • minute[s]
  • hour[s]
  • day[s]
  • week[s]
  • month[s]
  • year[s]
• The special word next followed by a one of the following words:
  • minute[s]
  • hour[s]
  • day[s]
  • week[s]
  • month[s]
  • year[s]

Security

Auditing Events

If the auditing subsystem is properly configured and is enabled, the at command generates the following audit record or event every time the command is run:

For more details about how to properly select and group audit events, and how to configure audit event data collection, see Setting Up Auditing in AIX® Version 7.1 Security.

Attention RBAC users and Trusted AIX users: This command can perform privileged operations. Only privileged users can run privileged operations. For more information about authorizations and privileges, see Privileged Command Database in Security. For a list of privileges and the authorizations associated with this command, see the lssecattr command or the getcmdattr subcommand.

Exit Status

This command returns the following exit values:

Examples

1. To schedule the command from the terminal, enter a command similar to one of the following:

   If uuclean is in your current directory, enter:

   at   5   pm   Friday
   uuclean
   <Ctrl-D>
    
   at   now   next   week
   uuclean
   <Ctrl-D>

   If uuclean is in $HOME/bin/uuclean, enter:

   at   now   +   2   days
   $HOME/bin/uuclean
   <Ctrl-D>

   Note: When entering a command name as the last item on the command line, a full path name must be given if the command is not in the current directory, and the at command will not accept any arguments.
2. To run the uuclean command at 3:00 in the afternoon on the 24th of January, enter any one of the following commands:

   echo   uuclean   |   at   3:00   pm   January   24
    
   echo   uuclean   |   at   3 pm   Jan   24
    
   echo   uuclean   |   at   1500   jan   24

3. To have a job reschedule itself, invoke the at command from within the shell procedure by including code similar to the following within the shell file:

   echo   "ksh   shellfile"   |   at   now   tomorrow

4. To list the jobs you have sent to be run later, enter:

   at    -l

5. To cancel a job, enter:

   at    -r   ctw.635677200.a

   This cancels job ctw.635677200.a. Use the at -l command to list the job numbers assigned to your jobs.

Files