1728: Cron Mail

2016-09-02T13:32:28Z

Rincewind:

{{comic
| number = 1728
| date = September 2, 2016
| title = Cron Mail
| image = cron_mail.png
| titletext = Take THAT, piece of 1980s-era infrastructure I've inexplicably maintained on my systems for 15 years despite never really learning how it works.
}}

==Explanation==
{{incomplete|More detailed explanation off Cron (with wiki links). Why would it break because of Cueball's action and what is the "etc/". Title text not explained at all.}}
On Unix-like systems, [https://en.wikipedia.org/wiki/Cron cron] is a background process which allows one to schedule jobs to run at well-defined time slots.
It is conceptually the same software which has been used since, at least, the 1980s and is still heavily used in modern operating systems, for example in several linux distributions. Many administrational tasks on servers can be automated with cron, like monitoring or updates. Most people administrating a server-like system with a UNIX-like operating system will therefore know it, at least the basis.
When one of these jobs produces output, that output is sent as an email to the user, using the /usr/bin/sendmail program. A common situation on many unix-like systems is that sendmail (or the program implementing that binary, like exim or postfix) is not configured to send email to the actual email address of the person behind the user account that configured the cron job. In that situation, the default is often to write the mail in question to /var/mail/username, in mbox format.

The "/etc" directory is used for configuration files on UNIX-systems, therefore "/etc/crontab" is the main configuration file of cron.

Most shells will check that file, and produce a message "You have new mail" when its timestamps have changed.

[[Cueball]] is not aware of all of the above, and expresses surprise at the repeated messages. [[Ponytail]] tells him to check /var/mail/cueball, When he realizes what has happened, he configures the mail system so that it writes all mail for his user to the cron configuration, thereby probably breaking it and ensuring that the shell will stop producing "You have new mail" messages.

==Transcript==
:[Cueball is sitting at a table in an office chair working on his laptop. Ponytail walks up to him.]
:Cueball: I've been getting these "You have new mail" UNIX notifications for like 15 years, but I've never bothered to figure out what it's talking about.

:[Ponytail has stopped behind Cueball who is typing on his laptop. When Ponytail (and later Cueball) mentions code, the text uses both small and capital letters (as opposed to only capital letters in all other text).]
:Ponytail: Look in /var/mail?
:Cueball: OK...
:Cueball: Oh, wow, there's like a gigabyte of stuff from Cron in here.

:[In a frame-less panel Ponytail is facepalming. Cueball is replying from off-panel with a starburst indicating his position.]
:Ponytail: *Sigh*
:Ponytail: You should fix your Cron, then point "MAILTO=" somewhere you actually see-
:Cueball (off-panel): Better idea:

:[Same setting as panel 2 but Cueball is visibly typing on the laptop as shown with three small curved lines over his hands on the keyboard.]
:Cueball: export MAILTO=/etc/crontab
:Cueball: There. Your move, Cron.
:Ponytail: Wow. Hardball.
:Cueball: Let's see how important it thinks that mail really is.

{{comic discussion}}

[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Cueball]]
[[Category:Computers]]

Talk:1728: Cron Mail

2016-09-02T13:09:28Z

Rincewind:

I think the "MAILTO" variable in "/etc/crontab" is meant, so only only cron-mails would go to this address, not all mails for the user

[[User:Rincewind|Rincewind]] ([[User talk:Rincewind|talk]]) 13:09, 2 September 2016 (UTC)

explain xkcd - User contributions [en]

1728: Cron Mail

Talk:1728: Cron Mail