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UNIX for Dummies Questions & Answers
crontab problem
Post 10130 by Kelam_Magnus on Thursday 8th of November 2001 09:34:42 AM
11-08-2001
crontab options
Guest100,
I used to use only "crontab -e" until I found this way of editing the crontab. It is much safer for you and if you make any mistakes it doesn't corrupt your crontab file.
When you look at the options for the manpage for crontab, the first options is "crontab filename".
My only point about saving the crontab out to a file and editing it is 1) so that you will have a copy of it and 2) when you edit this text file that you just saved out, you can execute "crontab filename" to replace the current crontab with the newly edited one. In addition, it prevents you from making a mistake typing while using "crontab -e".
Step 1
Copy out the crontab to a saved file.
$ crontab -l > somefile
Step 2
edit somefile and make changes.
$ vi somefile
Step 3
copy the newly edited file back into place.
$ crontab somefile
This is the safest way to edit the crontab file so that it doesn't get corrupted.
I work for a very large telecom company and this is the company standard for all platforms: SUN, HPUX, and AIX with several different versions on each platform.
In addition, yes you can go to /usr/spool/cron/crontabs and vi the file in question, edit it and save. The file will be recognized by cron because I have done this as well. I have even cut and pasted from a Word document into a telnet session while vi'ing a file in /usr/spool/cron/crontabs file. And there was no corruption of the file when I saved it and ran cron.
Trust me, all of these things work! Can someone else back me up on this? I am not trying to mess you up, only to help you out.
I used to use only "crontab -e" until I found this way of editing the crontab. It is much safer for you and if you make any mistakes it doesn't corrupt your crontab file.
When you look at the options for the manpage for crontab, the first options is "crontab filename".
My only point about saving the crontab out to a file and editing it is 1) so that you will have a copy of it and 2) when you edit this text file that you just saved out, you can execute "crontab filename" to replace the current crontab with the newly edited one. In addition, it prevents you from making a mistake typing while using "crontab -e".
Step 1
Copy out the crontab to a saved file.
$ crontab -l > somefile
Step 2
edit somefile and make changes.
$ vi somefile
Step 3
copy the newly edited file back into place.
$ crontab somefile
This is the safest way to edit the crontab file so that it doesn't get corrupted.
I work for a very large telecom company and this is the company standard for all platforms: SUN, HPUX, and AIX with several different versions on each platform.
In addition, yes you can go to /usr/spool/cron/crontabs and vi the file in question, edit it and save. The file will be recognized by cron because I have done this as well. I have even cut and pasted from a Word document into a telnet session while vi'ing a file in /usr/spool/cron/crontabs file. And there was no corruption of the file when I saved it and ran cron.
Trust me, all of these things work! Can someone else back me up on this? I am not trying to mess you up, only to help you out.
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LEARN ABOUT REDHAT
crond
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)