Tip (and Question) regarding crontab sysadministration

[Thad P Floryan]

In a quest to simplify system administration, I desired to make the cronlog
easier to scan for any "funny business."  As you know, the use of "here is"
files (e.g. command << FOO ...text... FOO) implied by using a crontab entry
such as:

16,46 *  *  *  *  /bin/su uucpadm %   /usr/lib/uucp/uudemon.admin >/dev/null

produces a very cluttered cronlog.  After RTFM for sh(1), ksh(1), su(1), it
still wasn't clear WHY some of the default crontab entries are like the above
entry (ref. ``%'') and why some are like the following (ref. ``-c "...." ''):

18,48 *  *  *  *  /bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour  >/dev/null"

crontab entries (at least on my systems) are executed as "root", so I figured
I'd switch to using "-c" for all crontab entries and see a readable cronlog.

A few entries had to be changed from "/bin/su" to "/bin/sh", but otherwise
everything works fine (even with /bin/ksh as root's shell in /etc/passwd) and
an extraction of crontab now looks like:

16,46 *  *  *  *  /bin/su uucpadm -c "/usr/lib/uucp/uudemon.poll   >/dev/null"
18,48 *  *  *  *  /bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour   >/dev/null"
00    4  *  *  *  /bin/su uucpadm -c "/usr/lib/uucp/uudemon.admin  >/dev/null"
59   23  *  *  *  /bin/sh         -c "/usr/local/bin/hdwarn.day    >/dev/null"
59   23  *  *  *  /bin/sh         -c "/usr/local/bin/du-logs.day   >/dev/null"
03    3  *  *  0  /bin/sh         -c "/etc/clockupd.wk             >/dev/null"
30    5  *  *  1  /bin/su uucpadm -c "/usr/lib/uucp/uudemon.cleanu >/dev/null"
30    5  *  *  1  /bin/sh         -c "/etc/cleanup.wk              >/dev/null"

and a corresponding sample of cronlog output now looks like the following
two hours' entries:

Mon Jan 29 23:00:00 1990

/bin/su uucpadm -c "/usr/lib/uucp/uudemon.poll    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.poll    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour    >/dev/null"
/bin/sh         -c "/usr/local/bin/hdwarn.day     >/dev/null"
/bin/sh         -c "/usr/local/bin/du-logs.day    >/dev/null"

Sun Feb  4 03:00:00 1990

/bin/sh         -c "/etc/clockupd.wk              >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.poll    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.poll    >/dev/null"
/bin/su uucpadm -c "/usr/lib/uucp/uudemon.hour    >/dev/null"

I've been running one system this way for over a week now with no apparent
problems.  As you can see, the cronlog entries are far easier to quickly scan.
I trust you find this tip useful!

However, I'm still puzzled why ALL the default examples I've seen in crontabs
on many systems mix both the "%" and "-c" usage in the same file.  Is there
any real reason for invoking (otherwise similar) scripts using one method or
the other?

Thad Floryan [ thad at cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]