Title text: He sees you when you're sleeping, he knows when you're awake, he's copied on /var/spool/mail/root, so be good for goodness' sake.
This comic was posted on Christmas Eve. While Christmas is principally a Christian holiday, celebrating the birth of Jesus on December 25, there are many traditions around it, among them a tradition that on Christmas Eve Santa Claus will make his round delivering gifts to good children.
Rob sits behind a UNIX computer and tried to change his user account from his normal access to the access of a super user by using the command "sudo su". Sudo is a famous phrase in xkcd lore, made famous by comic 149: Sandwich. Before allowing administrator access (as root user), it asks for a password. The field is blank because, in most UNIX systems, the characters of the password are not shown. When Rob is unable to use the command his account is not authorized and the system says that the incident "will be reported" (usually to the system administrator, so he can see if someone is making repeated attempts at accessing administrator privileges).
In the comic, however, sudo and the system report the incidents to Santa Claus, who, in Christmas lore, makes a list of who is naughty and who is nice. If you are nice then you get presents, while if you are naughty, you get a lump of coal. When sudo reports to Santa that Rob's account is not authorized, he puts Rob on the naughty list.
In the title text, which is a parody of the famous Christmas song, "Santa Claus Is Coming To Town",
/var/spool/mail/root is the root (superuser) mailbox on a Linux system, where the incident described in the comic would commonly be reported to.
- [Rob is sitting at a computer. The computer's prompt is shown.]
[email protected]~$ sudo su
robm is not in the sudoers file. This incident will be reported.
[email protected]~$ █
- [Megan approaches.]
- Rob: Hey — who does sudo report these "incidents" to?
- Megan: You know, I've never checked.
- [Santa Claus is sitting at a desk supported by candy canes, with a red monitor. On the wall are two lists labeled 'naughty' and 'nice'. He is in the process of adding a line to the 'naughty' list.]
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