at

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at is a tool for running delayed jobs and batching processes. Processes can be scheduled via 12 or 24 hour time in HH:MM notation. If that time is already passed, the next day is assumed. It's also possible to specify a job's time with a few different aliases, notably: midnight (00:00), noon (12:00), and teatime (16:00). Relative times are also acceptable.

It is also possible to schedule a job contingent upon acceptable system load via the batch command.

Installation

USE flags

USE flags for sys-process/at Queues jobs for later execution

`pam`	Add support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip
`selinux`	!!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur

Data provided by the Gentoo Package Database · Last update: 2024-09-12 18:37 More information about USE flags

Emerge

root #emerge --ask sys-process/at

Environment variables

LOGNAME — if the user is not logged in at the time of the at job's scheduled execution, mail is sent to the user account specified in this variable.
SHELL — used by at at execution time to determine the appropriate shell.

Files

/var/spool/at/atjobs — The directory for storing scheduled jobs.
/var/spool/at/atspool — The directory for storing the output of completed jobs.
/proc/loadavg — The system's load average.
/var/run/utmp — Account login records.
/etc/at/at.allow — The system whitelist for determining who may submit at batch jobs.
/etc/at/at.deny — The system blacklist for preventing abuse of at batch jobs.

Service

The atd service is required in order for at batch job execution to occur. It can be enabled as follows:

OpenRC

root #rc-update add atd default

root #rc-service atd start

runit

root #ln -s /etc/sv/atd /var/service/

root #sv up atd

systemd

root #systemctl enable atd

root #systemctl start atd

Usage

at

List scheduled jobs:

user $at -l

10	Mon Mar 20 08:15:00 2023 a alice 
11	Mon Mar 20 09:45:00 2023 a bob

Pipe a simple command to at and have it run in 5 minutes.

user $echo -e "testing, testing, 1, 2, 3" | at now +5 minutes

Delete scheduled jobs:

user $at -r 11

atrun

Define the system load below which scheduled jobs are permitted to run. For example, given a 4 core system running batch jobs with a system load of 3.0 might be far more realistic than the 0.8 default.

user $atrun -l 3.0

atq

List scheduled jobs:

user $atq

10	Mon Mar 20 08:15:00 2023 a alice 
11	Mon Mar 20 09:45:00 2023 a bob

atrm

Delete a scheduled job:

user $atrm 11

batch

Note
The compile time default for batch is a system load of 0.8, which may not be what you want on a modern multi-core system. To override this compile-time default use the atd -l command.

Run pending batch jobs when the current system load drops below a given threshold.

user $batch

Invocation

user $at -h

Usage: at [-V] [-q x] [-f file] [-u username] [-mMlbv] timespec ...
       at [-V] [-q x] [-f file] [-u username] [-mMlbv] -t time
       at -c job ...
       at [-V] -l [-o timeformat] [job ...]
       atq [-V] [-q x] [-o timeformat] [job ...]
       at [ -rd ] job ...
       atrm [-V] job ...
       batch

Removal

Unmerge

root #emerge --ask --depclean --verbose sys-process/at

at

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