Can cron write job output to a log *by default* (instead of mail)?

Solution 1:

The short answer is no, cron mails to the owner of the crontab by design. In the standard cron there is no way to change this.

The best I can think of is to configure the MTA's on the machines where you want this behavior to dump the mail in to a log file instead of a user mailbox.

Solution 2:

I am not sure what you mean exactly when you say "mail is disabled". But maybe you could set up an alias in /etc/aliases that is directed to a pipe? Something like

root: "|/bin/cat >> /var/log/cron.log"

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Solution 3:

I don't think what you're asking for is actually possible with Ubuntu (or any other) cron.

Aside from geekmonkeys idea, you could also set $MAILTO to a local account and route the output through procmail.