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I'm inspecting /var/spool/cron/atjobs/a001cf01570e44 with cat, after running the at command from PHP using exec().

It looks like at has prepended the script with lots of APACHE environment variables.

#!/bin/sh
# atrun uid=33 gid=33
# mail www-data 0
umask 22
APACHE_RUN_DIR=/var/run/apache2; export APACHE_RUN_DIR
APACHE_PID_FILE=/var/run/apache2.pid; export APACHE_PID_FILE
PATH=/usr/local/bin:/usr/bin:/bin; export PATH
APACHE_LOCK_DIR=/var/lock/apache2; export APACHE_LOCK_DIR
LANG=C; export LANG
APACHE_RUN_USER=www-data; export APACHE_RUN_USER
APACHE_RUN_GROUP=www-data; export APACHE_RUN_GROUP
APACHE_LOG_DIR=/var/log/apache2; export APACHE_LOG_DIR
PWD=/home/jordanarseno/webroot/public_html/myapp; export PWD
cd /home/jordanarseno/webroot/public\_html/myapp || {
     echo 'Execution directory inaccessible' >&2
     exit 1
}
curl -k http://localhost/myapp/crons/this_action/3

The last line is the only real command I sent along with at via stdin. What is the purpose of these variables? Where is this procedure stored?

Jordan Arseno
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1 Answers1

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When you invoke the at command it copies the current environment so that's what you're seeing.

The working directory, the environment (except for the variables TERM, DISPLAY and _) and the umask are retained from the time of invocation.

You are running at in a php script via apache so what you are seeing in the script is the environment etc that apache is running in.

user9517
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  • Thanks, what's the purpose though... What was the motivation for `at` to do this? And can I suppress them?... Or would it be wise not to do so? What is a command I could have handed to `exec()` that would be dependable on these variables? The reason I ask is I may have *many* scripts in the atjob directory and I'd like to keep them a small filesize. – Jordan Arseno Sep 29 '12 at 21:28
  • @JordanArseno: The purpose is so that your command/script runs in the same environment as the account that added it to the queue. Cron runs jobs under a restricted environment - you wouldn't believe the number of questions we get here which are solved because the cron job environment is different from the OPs command line environment - at doesn't suffer from this problem. Your script above is 633 bytes - on any reasonably modern system you'd need billions of jobs to cause space problems surely? – user9517 Sep 29 '12 at 21:49