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Revision as of 23:07, 7 August 2012

Welcome to the explain xkcd wiki! We currently have Expression error: Unrecognised punctuation character ",". comic explanations. Come and add yours!

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Hard Reboot
Googling inevitably reveals that my problem is caused by a known bug triggered by doing [the exact combination of things I want to do]. I can fix it, or wait a few years until I don't want that combination of things anymore, using the kitchen timer until then.
Title text: Googling inevitably reveals that my problem is caused by a known bug triggered by doing [the exact combination of things I want to do]. I can fix it, or wait a few years until I don't want that combination of things anymore, using the kitchen timer until then.


Ambox notice.png This explanation may be incomplete or incorrect: The sentence below the comic: Why everything I have is broken is not explained. Is this because he just crashes his server every day? Also the kitchen timer in the title text is not mentioned. It is not a kitchen timer that is used in the picture

This comic is about using a simple and unrelated trick to fix a problem.

Swap space is an area of a computer's hard drive reserved for use when the computer runs out of RAM. Ideally, RAM + SWAP >= MAX, where MAX is the amount of memory the computer will ever try to use at the same time. However, some [broken] programs may keep requesting memory from the system until computer runs out of resources. Alternatively, system may be misconfigured to run more and more programs simultaneously. Rebooting the computer will empty the RAM and swap space so resources can be reallocated, but this only temporarily alleviates the underlying issue. Determining the root cause of the problem is often nontrivial.

It would take up to 10 hours to figure out why the server is running out of swap space and fix the problem. Alternatively, Randall could just take 5 minutes and plug the server into a light timer. This attitude to problem solving is in contrast to the attitude shown in 974: The General Problem.

Timers like the one in the comic typically have four switches or notches per hour, so using the timer would replace an unpredictable and indefinite loss of service with a regular 15 minute downtime event once a day. Also, it can be scheduled during, say, the middle of the night when most users are sleeping to minimize disruption.

The correct method of scheduling a regular reboot would be using a cron task, but perhaps the server is "crashing" in such a dramatic manner that cron, or shutdown, or init stops working. The comic title alludes to this, in that a "hard" reboot scheduled with an analog timer is more guaranteed to work than a "soft" one scheduled with cron.

If a memory leak is not present, the problem might be fixable by simply increasing swap space, however if there is a more complex underlying issue, this is the first step along the path of 10 hours of troubleshooting. As a general stereotype, the type of person who has a home server is probably also the kind of person who would start by 'just' increasing the swap size, and before they know it has spent 10 hours completely engrossed in the challenge of fixing the problem. (See 349: Success)

The title text's first sentence refers to situations where the given solution to a problem is just the original problem rephrased to sound like a solution. It may also refer to bug trackers, where someone found out and posted what causes the issue, but the bug is marked as "Unresolved," "Waiting," or "Will not fix."

The title text's second sentence is about the human tendency to wait on someone else to fix a problem rather than doing it yourself. Since everyone is waiting on someone else to do it, such problems tend to never be fixed, hence the solution of "wait[ing] a few years until I don't want that combination of things anymore."


[Inside a frame there is two pictures. To the left there is a section of a computer screen with white text on a black background. The screen is covered in lines of illegible text.]
[Above the screen it says:]
Figuring out why my home server keeps running out of swap space and crashing:
[Below the screen it says:]
1-10 hours
[To the right there is a frame with a drawing of a timer plugged into a power port with cable running off to the side.]
[Above the frame it says:]
Plugging it into a light timer so it reboots every 24 hours:
[Below the frame it says:]
5 minutes
[Below the main frame]
Why everything I have is broken

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