Editing 1728: Cron Mail
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When a cron job produces output, cron's default behavior is to send an email to the user account under which the job ran. However, in most situations, an email address has not been set up for that user, so the email is instead written to a mailbox file. Most Unix shells will notify the user with a message like "You have new mail" when this mailbox file is updated, but if the user doesn't know how to check this mail file, they will likely just ignore the message. | When a cron job produces output, cron's default behavior is to send an email to the user account under which the job ran. However, in most situations, an email address has not been set up for that user, so the email is instead written to a mailbox file. Most Unix shells will notify the user with a message like "You have new mail" when this mailbox file is updated, but if the user doesn't know how to check this mail file, they will likely just ignore the message. | ||
− | In this case, Cueball has been ignoring his mailbox for fifteen years. When he finally learns where to look, he discovers more than a gigabyte worth of messages from the cron program, the vast majority of which are likely meaningless. Ponytail | + | In this case, Cueball has been ignoring his mailbox for fifteen years. When he finally learns where to look, he discovers more than a gigabyte worth of messages from the cron program, the vast majority of which are likely meaningless. Ponytail suggests that Cueball "fix your cron" (likely meaning to fix the task that's generating the output so that it doesn't do so), then set a parameter that tells cron to send email to an address he actually checks. (He could also opt to direct the mails to <code>/dev/null</code>, which would simply discard them). Cueball, however, interprets the tremendous amount of email as spam and decides to redirect the emails to <code>/etc/crontab</code>, the main configuration file that contains all of cron's scheduling information. He apparently believes that this will either stop the emails or cause cron to spam itself instead. |
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+ | In reality, this will most likely break cron entirely, as the text output from the cron jobs is unlikely to be in the same format as a valid schedule entry in the crontab file. Invalid scheduling information will cause cron to ignore the file - this will then cause it to have no scheduled jobs at all, and it will simply do nothing after the first job that sends itself an email. Cueball will, in fact, have stopped the tide of cron spam, but will likely cause bigger problems due to the sudden lack of critical system maintenance tasks. | ||
The title text shows that Cueball is somewhat aware of what cron does, including the fact that it's existed pretty much unchanged for several decades, but he hasn't bothered to really get into understanding it, treating it more as a foe to vanquish rather than as a tool to understand and use. | The title text shows that Cueball is somewhat aware of what cron does, including the fact that it's existed pretty much unchanged for several decades, but he hasn't bothered to really get into understanding it, treating it more as a foe to vanquish rather than as a tool to understand and use. |