07-08-2002
I'm not sure of what you are asking but I think you are confusing going from console and changing root's crontab on a system versus going from another server (telnet, ssh....) to a system and changing root's crontab.
The crontab for root is a file (as you specified, /var/spool/cron/crontabs/root). To change the crontab for root, use the crontab -e command (read the man page on crontab first). The system will start some type of editor session - so it's like editing any other file at that point. You make changes, save, and exit the editor.
Quote:
if the root cron reach its maximum capacity how the unix will handle the incoming cron job from the console.
I have never heard of a maximum capacity for cron - I doubt you could reach it since those of us who have mistakenly created incorrect entries in cron which have created multiple processes in seconds can tell you, it won't be the crontab that gets to a maximum but the server - with runaway processes in endless loops. The most entries I have seen in a crontab to date: 171 (a DBA who has so much running in cron, I don't think he even needs to come to work anymore).
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CRON(8) System Manager's Manual CRON(8)
NAME
cron - daemon to execute scheduled commands (Vixie Cron)
SYNOPSIS
cron
DESCRIPTION
Cron should be started from /etc/rc or /etc/rc.local. It will return immediately, so you don't need to start it with '&'.
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, which are in a different format (see crontab(5)). Cron then
wakes up every minute, examining all stored crontabs, checking each command to see if it should be run in the current minute. When execut-
ing commands, any output is mailed to the owner of the crontab (or to the user named in the MAILTO environment variable in the crontab, if
such exists).
Additionally, cron checks each minute to see if its spool directory's modtime (or the modtime on /etc/crontab) has changed, and if it has,
cron will then examine the modtime on all crontabs and reload those which have changed. Thus cron need not be restarted whenever a crontab
file is modified. Note that the Crontab(1) command updates the modtime of the spool directory whenever it changes a crontab.
SEE ALSO
crontab(1), crontab(5)
AUTHOR
Paul Vixie <paul@vix.com>
4th Berkeley Distribution 20 December 1993 CRON(8)