12-30-2010
Quote:
Which is the preferred method to modify crontabs. To issue the crontab –e or to edit the file and reset it using the crontab [filename] method?
Personally I always extract a crontab file twice to an editing area using "crontab -l" redirected once under its correct name and once with a date suffix.
I never use "crontab -e" and prefer to edit the crontab in the editing area under its correct name with say "vi" and then finally publish the end-product with "crontab". At the final publish stage the "crontab" command validates the file.
There are several advantages with this approach:
1) You always have a backup. (It is remarkably easy to wipe a crontab file).
2) You have before and after files which you can check with "diff" before publishing the crontab.
3) You have control over when your crontab becomes live. I have prepared and checked an edited crontab in advance by this method. I have also taken lines from a test system crontab and injected them into the live crontab by this method.
4) You create an archive of changes which can be useful for looking up what you did last time.
5) On some sites such an audit trail is mandatory.
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LEARN ABOUT MOJAVE
crontab
CRONTAB(1) BSD General Commands Manual CRONTAB(1)
NAME
crontab -- maintain crontab files for individual users (V3)
SYNOPSIS
crontab [-u user] file
crontab [-u user] { -l | -r | -e }
DESCRIPTION
The crontab utility is the program used to install, deinstall or list the tables used to drive the cron(8) daemon in Vixie Cron. Each user
can have their own crontab, and they are not intended to be edited directly.
(Darwin note: Although cron(8) and crontab(5) are officially supported under Darwin, their functionality has been absorbed into launchd(8),
which provides a more flexible way of automatically executing commands. See launchctl(1) for more information.)
If the /usr/lib/cron/cron.allow file exists, then you must be listed therein in order to be allowed to use this command. If the
/usr/lib/cron/cron.allow file does not exist but the /usr/lib/cron/cron.deny file does exist, then you must not be listed in the
/usr/lib/cron/cron.deny file in order to use this command. If neither of these files exists, then depending on site-dependent configuration
parameters, only the super user will be allowed to use this command, or all users will be able to use this command. The format of these
files is one username per line, with no leading or trailing whitespace. Lines of other formats will be ignored, and so can be used for com-
ments.
The first form of this command is used to install a new crontab from some named file or standard input if the pseudo-filename '-' is given.
The following options are available:
-u Specify the name of the user whose crontab is to be tweaked. If this option is not given, crontab examines ``your'' crontab, i.e.,
the crontab of the person executing the command. Note that su(1) can confuse crontab and that if you are running inside of su(1) you
should always use the -u option for safety's sake.
-l Display the current crontab on standard output.
-r Remove the current crontab.
-e Edit the current crontab using the editor specified by the VISUAL or EDITOR environment variables. The specified editor must edit
the file in place; any editor that unlinks the file and recreates it cannot be used. After you exit from the editor, the modified
crontab will be installed automatically.
FILES
/usr/lib/cron/cron.allow
/usr/lib/cron/cron.deny
DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command line.
SEE ALSO
crontab(5), compat(5), cron(8), launchctl(1)
STANDARDS
The crontab command conforms to IEEE Std 1003.2 (``POSIX.2''). The new command syntax differs from previous versions of Vixie Cron, as well
as from the classic SVR3 syntax.
AUTHORS
Paul Vixie <paul@vix.com>
BSD
December 29, 1993 BSD