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Crond Demystified !!

Wed, 02/23/2005 - 15:17 — nepalexpo

In Linux Fedora Core 1, "crond" is started from the script "/etc/rc.d/init.d/crond". The manual `man cron` says that cron searches "/var/spool/cron" for crontab files which are named after accounts in "/etc/passwd"; crontabs found are loaded into memory. Cron also searches for "/etc/crontab" and the files in the "/etc/cron.d/" directory.

The "/etc/crontab" file contains the following.

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root
HOME=/

# run-parts
01 * * * * root run-parts /etc/cron.hourly
02 4 * * * root run-parts /etc/cron.daily
22 4 * * 0 root run-parts /etc/cron.weekly
42 4 1 * * root run-parts /etc/cron.monthly

The "/etc/cron.d" directory contains nothing. So clearly, all system cron are in the /etc/cron.* files. The above commands mean that the program "run-parts" will be run as user "root" for each of the scripts.

The command "run-parts" turns out to be the script "/usr/bin/run-parts", as follows.

#!/bin/bash
 
# run-parts - concept taken from Debian
 
# keep going when something fails
set +e
 
if [ $# -lt 1 ]; then
        echo "Usage: run-parts <dir>"
        exit 1
fi
 
if [ ! -d $1 ]; then
        echo "Not a directory: $1"
        exit 1
fi
 
# Ignore *~ and *, scripts
for i in $1/*[^~,] ; do
        [ -d $i ] && continue
        # Don't run *.{rpmsave,rpmorig,rpmnew,swp} scripts
        [ "${i%.rpmsave}" != "${i}" ] && continue
        [ "${i%.rpmorig}" != "${i}" ] && continue
        [ "${i%.rpmnew}" != "${i}" ] && continue
        [ "${i%.swp}" != "${i}" ] && continue
        [ "${i%,v}" != "${i}" ] && continue
 
        if [ -x $i ]; then
                $i 2>&1 | awk -v "progname=$i" \
                              'progname {
                                   print progname ":\n"
                                   progname="";
                               }
                               { print; }'
        fi
done
 
exit 0

In essence, this just runs all of the scripts in the specified directory. E.g. each hour, the executable plain files in /etc/cron.hourly are run.

See also crontab tutorial.

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Wed, 03/09/2005 - 20:02 — michaellee job sequence in cron.daily

Hi,
I have created a job in cron.daily for backup. Before backup, i would like to perform logrotate (which is also in cron.daily). However, the job sequence is first backup and then logrotate. I have modified run-parts to list all jobs in cron.daily and the sequence is in alphabetic order (which is what i wanted). However, the job log send to root account indicate a different sequence. Why? How to control the sequence?

(I'm use fedora 2 but the run-parts is just the same as the one posted)
Regards,
Michael

Wed, 03/09/2005 - 21:58 — nepalexpo sequencing jobs

Try renaming "logrotate" to "0logrotate". That is a zero prefix.

Wed, 03/09/2005 - 22:35 — michaellee Sequencing Jobs

Good suggestion. I'll try and see whether it work.

However, i just don't know why the sequence displayed by my test script no match execution sequence.

#!/bin/bash

# run-parts - concept taken from Debian

# keep going when something fails
set +e

if [ $# -lt 1 ]; then
echo "Usage: run-parts dir"
exit 1
fi

if [ ! -d $1 ]; then
echo "Not a directory: $1"
exit 1
fi

# Ignore *~ and *, scripts
for i in $1/*[^~,] ; do
[ -d $i ] && continue
echo "${i}"
done

exit 0

Regards,
Michael

Thu, 03/10/2005 - 21:44 — michaellee Job Sequence

After modify the script name from logrotate to 0logrotate, logrotate is executed before backup.
Thanks.

Comment