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Scheduling AFS Cron Jobs -- The 'acrontab' Command

  Rainer Toebbicke CN/DCI

A new command, 'acrontab' , is now available (on ASIS) for the automatic scheduling of periodic jobs (cron) to be run with valid AFS tokens.

The command format is similar to the normal (SysV) crontab command:

• 'acrontab' without any arguments reads your acrontab entries from stdin,
• 'acrontab -l' lists your cron jobs,
• 'acrontab -e' invokes $VISUAL or $EDITOR on your acrontab.

cron jobs are triggered by acrontab entries which are kept on a central server. The jobs themselves are run on a machine of the user's choice. The format of the acrontab entries is the usual SysV (to be precise: AIX) crontab one, except that the command field must start with the IP node name of the node the command is to be executed on. For more details, consult the 'acrontab' man page.

An example:

rsrtb> acrontab
18 22 * * *  rsrtb date
/usr/afsws/bin/tokens
scripts/do_my_backup
<ctrl-D key pressed>
rsrtb>

creates a cron job that executes 'date', 'tokens' and the script 'do_my_backup' on 'rsrtb' every day at 22:18.

The cron-job's output is returned as a mail message to userid@afsmail (from where it can be '.forward'ed elsewhere. The job starts in the user's home directory with a fresh AFS token which is valid for the standard token lifetime (currently 25 hours). In the above example it was assumed that the do_my_backup script resides in the user's ~/scripts directory.

Prerequisites:

1.

in order to use the 'acrontab'

command, the user must hold a valid Kerberos ticket. Normally this is the case on machines using AFS-integrated login.

2.

the node on which the command is to be executed has SUE and the SUE-feature 'arc' installed. This is indicated by the presence of /usr/sue/etc/config/arc. The prerequisite of SUE currently restricts this to IBM, HP and Sun (Solaris). In case of doubt contact aix.support (or hp.support or sun.support). More information about SUE is in

http://wsspinfo.cern.ch/file/doc/sue/sue.html

3.

acrontab-triggered cron jobs are subject to the normal cron restrictions as imposed by cron.allow and cron.deny files in the directory applicable to the target system. The system administrator may therefore select who is allowed to run 'cron' (and 'acron') jobs. On most systems the default is to allow jobs from everybody.