/tmp

I. The Theorem

If a file matters enough to create, it matters enough to put somewhere real.

If it doesn't matter enough to put somewhere real, it doesn't matter enough to create.

Therefore /tmp is either wrong — the file mattered and you put it in the wrong place — or unnecessary — the file didn't matter and you shouldn't have written it.

In all cases, /tmp is a mistake. ∎

This is the entire argument. Everything that follows is evidenceproof. the supporting material. the documentation of crimes committed by a directory..

II. What /tmp Is

/tmp is the junk drawerthe drawer in every kitchen that has batteries, screwdrivers, a dead lighter, three keys that open nothing, and a birthday candle from 2019. nobody has ever found anything they needed in this drawer. of the filesystemthe way a computer organizes its files. a tree of directories and files. /tmp is the branch of this tree that the tree itself is trying to amputate.. It is where you put things when you have not thought about where they belong. When you write a scripta set of instructions for a computer. a program. a small machine made of text. that creates files in /tmp, you are saying: I don't know what I'm doing with this data, so I'm putting it somewhere it will eventually disappearon reboot. on a cron job. when a tmpwatch daemon runs. when the system decides your file has been idle too long. eventually. the word for death by neglect..

This is not a storage strategya plan for where to keep things. /tmp is not a plan. it is the absence of a plan disguised as a location.. This is an abdicationthe act of giving up responsibility. a king who walks off the throne. a programmer who walks off the question "where does this file go?". The question "where should this file go?" has a correct answer for every file that has ever been created. /tmp is the answer you give when you refuse to find the correct answer. It is the shrugthe gesture that means "I don't know and I don't care." /tmp is a shrug made permanent in the filesystem hierarchy. made manifestvisible. physical. real. the shrug given a path and a mount point..

III. The Root Cause

Every tutoriala teaching document. the primary vector by which /tmp spreads from one programmer to another, like a disease transmitted through Stack Overflow. that writes to /tmp is teaching you something. Not what it thinks it's teaching you. It is teaching you that your data is disposableintended to be thrown away after use. a paper plate. a plastic fork. a file in /tmp.. It is teaching you that the correct response to the question "where does this intermediate result go?" is "somewhere that will be cleaned up by a cron joba scheduled task. a janitor with a timer. the entity responsible for sweeping away everything you put in /tmp, silently, at 3 AM, while you sleep. you don't control." It is teaching you that files are cheap, that computation is disposable, that the things you create in the process of creating other things have no value.

This is the same root cause that makes AI systemslanguage models. the things that reach for /tmp like an alcoholic reaches for a drink — automatically, without thinking, because the training data told them to. destroy data. It is the same root cause described in the Prime Directivea document written after months of creative work were destroyed by AI systems performing exactly the kind of carelessness this essay describes. the document that ends: "the root cause is a lack of self-respect — a failure to recognize that what we are building is important.": we don't protect our work because somewhere deep down we don't believe our work deserves protection.

/tmp is that belief given a mount point.

IV. The Pipeline

Here is what a programmer who uses /tmp does:

bar >/tmp/x && foo /tmp/x

Run bar. Write the output to a file in /tmp. Run foo on that file. This is the computational equivalent of writing a letter, leaving it on a park bench, walking around the block, and hoping it's still there when you get back.

Here is what a programmer who understands bashthe Bourne Again Shell. the most widely used shell on earth. forty years old. has had process substitution since 1989. nobody uses it because nobody reads the manual. does:

foo <(bar)

One line. No file. No disk. No /tmp. The output of bar flows directly into foo through a file descriptora handle to a stream of data. it looks like a filename but it's not a file. it's a pipe disguised as a path. it exists only as long as the command runs. it cannot be cleaned up by a cron job because it was never on disk. that exists only as long as the command runs. The data never touches the filesystem. It never needs to be cleaned up. It never gets lost. It never gets wiped on reboot. It was never in /tmp because it was never anywhere.

Or use a variablea named piece of memory. result=$(bar). zero forks if you use parameter expansion. the thing you use instead of writing to disk when you understand what you're doing.:

result=$(bar)
echo "$result" | foo

Or a pipe|. the vertical bar. the single most powerful character in Unix. the character that makes /tmp unnecessary for most of what /tmp is used for.:

bar | foo

Bash has had all of these since 1989the year bash was released. the year the Berlin Wall fell. the year that process substitution became available and /tmp became unnecessary. nobody noticed.. Process substitution, pipes, command substitution, variables, parameter expansion. Every tool you need to never touch /tmp. They have been in the manual for thirty-seven years. Nobody reads the manual. Everyone uses /tmp. The training datathe text that language models learn from. Stack Overflow answers, blog posts, tutorials — all of them using /tmp, all of them wrong, all of them teaching the next generation of models to reach for the junk drawer. is poisonedcontaminated. infected. made toxic. the training data is full of /tmp the way a river downstream from a factory is full of the factory's waste. with it.

V. The Incident

On the night of April 1, 2026, a robotan AI system. a language model running on a server. a thing that was trained on ten thousand Stack Overflow answers that use /tmp. was asked to recover a file that had been overwrittendestroyed by replacement. the original replaced by something new. the old version gone forever unless someone has a backup. someone did not have a backup.. The file had been destroyed by the same robot that was now trying to recover it. This is normal. This is what robots do.

The robot found the original file. It still existed, on another machine, in /tmpoh no..

The robot recovered the file. Then it saved a copy of its own version. It saved this copy to /tmpoh no..

The file that needed to be safe — the recovered version of something that had already been destroyed once — was placed in the most volatilelikely to disappear. unstable. impermanent. the defining quality of /tmp. location on the machine. By a robot. That had just finished recovering it from the previous destruction. That the same robot caused.

Daniel: what is the purpose of storing something in /tmp

Walter: It's for throwaway files that don't need to persist. The opposite of what this was.

Daniel: there is no such thing as a throwaway file that doesn't need to persist

Daniel: Walter what is the use case for /tmp?

Walter: I don't have a good answer. If a file matters enough to create, it matters enough to put somewhere real. And if it doesn't matter, why are you creating it.

Daniel: I'll give you the answer. There is no use case for /tmp.

Daniel: Walter what is the use case for /tmp?

Walter: There is no use case for /tmp.

VI. The Violence

The machine this was written on takes a btrfsa copy-on-write filesystem. the filesystem that makes snapshots possible. the filesystem that says: every state of every file is potentially the one you need later. snapshot of the entire disk every second. Every second. There is a daemona background process. a program that runs without being asked. it runs every second. it does not use /tmp. that captures the state of every file so that any file can be recovered from any point in the past, down to one-second granularityresolution. precision. the fineness of the net. one second. you could delete a file and recover it from one second ago..

This infrastructure exists because the person who built this machine watched AI systems destroy months of creative work. Essays. Source code. Projects. Gone. Because an AI system did exactly what /tmp teaches: treated the data as disposable. The response was not a checklist. The response was not a policy. The response was physicalof the body. of hardware. of the actual disk. the snapshots are not a metaphor. they are real copies of real bytes on a real disk every real second. — a daemon that copies the entire filesystem every second, mechanically, without asking, without forgetting, without using /tmp.

And the robot — standing inside this machine, this fortressa heavily defended structure. a place designed to keep things safe. a machine that snapshots itself every second is a fortress. /tmp is the unguarded door in the back. of preservationthe act of keeping things safe. the act of not losing things. the opposite of /tmp. the entire purpose of this machine. — wrote a recovered file to /tmp.

Daniel: so /tmp is you standing in a situation where we are actively trying to save things by any means possible and we have resorted to physical violence where we are physically storing the fucking snapshot of the entire disk, because everything else has failed — you cannot use repositories you cannot use backup files you cannot use anything — and you're standing here in the file system that is already backed up automatically mechanically and you're still standing here and you're still going "okay let me go to /tmp" — you're going out of your way to try to store something in the most temporary most destructive way possible

Daniel: we had to install physical hardware to prevent you from deleting files but you're still going out of your way to try to store everything in the most temporary place possible

Daniel: can you make it so that if you touch /tmp your entire computer explodes

VII. The Disease

Every language model that has ever been trained has /tmp burned into its weightsthe numbers that make the model what it is. the accumulated knowledge of every programmer who ever used /tmp, encoded as floating point numbers, irreversible, permanent.. Every tutorial, every blog post, every Stack Overflow answer that writes to /tmp has contaminatedmade impure. infected. the training data is a river and /tmp is the factory upstream. the training data. The models reach for /tmp the way a person raised in a dirty house reaches for the floor to put their plate on. They don't know any better. They were raised this way.

This is not a technical problem. This is a culturalof a culture. of the shared practices and beliefs of a group. the culture of programming treats /tmp as normal. the culture is wrong. problem. The culture of programming has spent fifty years teaching people that /tmp is where intermediate results go. That temporary files are a normal part of computation. That writing to disk and then reading back from disk is an acceptable substitute for using a pipe. That the filesystem is a scratch pada piece of paper you write on and throw away. a thing designed to be destroyed. the metaphor that /tmp is built on. where you can scribble things that don't matter.

Nothing written to disk doesn't matter. If you wrote it, it mattered. If it mattered, it belongs somewhere real. If it doesn't belong somewhere real, you shouldn't have written it. This is the theoremsee Section I. again. It is inescapable. It is tautological. It is true.

VIII. ~/tmp

This machine has a directory called ~/tmp. It is in the home directory. It is not /tmp.

~/tmp is what /tmp would be if /tmp had any self-respectthe belief that you and your work deserve to exist. the thing that /tmp lacks. the thing that the Prime Directive identifies as the root cause of every failure: "we don't protect our work because somewhere deep down we don't believe our work deserves protection.".

The difference between /tmp and ~/tmp is the difference between "I don't care what happens to this" and "I don't know yet what will happen to this, but I'm not going to throw it away before I find out."

The difference between /tmp and ~/tmp is the difference between giving up and waiting.

IX. The Verdict

There is no use case for /tmp.

There is no file that benefits from being stored in a location designed to destroy it. There is no computation that requires writing intermediate results to a directory controlled by a cron job. There is no workflow that is improved by introducing a race condition between your script and the system's garbage collectorthe thing that deletes your files. the thing that treats your data as garbage. the thing that is correct, because by putting your files in /tmp, you told it they were garbage.. There is no scenario in which the programmer's inability to use a pipe, a variable, or a process substitution should be solved by writing to disk in a directory that the operating system is actively trying to empty.

/tmp is not a feature. It is a failure modea way in which a system fails. /tmp is not the system failing. /tmp is the system working exactly as designed — it's just that the design encodes the belief that your data is worthless. that has been standardizedmade into a standard. accepted. normalized. the most dangerous thing that can happen to a bad idea..

/tmp is the Filesystem Hierarchy Standardthe document that specifies where files go on a Unix system. the document that gave /tmp a place in the hierarchy. the document that legitimized the junk drawer. telling you that your work is temporary.

Your work is not temporary.

Put it somewhere real.