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. | ||
| β | 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 his 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 discard them, or simply disable the mail in the crontab.) 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. |
In reality, this will not cause significant problems as the <code>MAILTO</code> environmental variable in cron takes an email address or usernames on the local system and attempts to send emails to them. It will not write or append output to a local file like <code>/etc/crontab</code>. Thus when cron attempts to email <code>/etc/crontab</code> the mail program cron uses will generate an error saying it can't find the user <code>/etc/crontab</code>. | In reality, this will not cause significant problems as the <code>MAILTO</code> environmental variable in cron takes an email address or usernames on the local system and attempts to send emails to them. It will not write or append output to a local file like <code>/etc/crontab</code>. Thus when cron attempts to email <code>/etc/crontab</code> the mail program cron uses will generate an error saying it can't find the user <code>/etc/crontab</code>. | ||
