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Comment by cryptonector | Hacker News Reader

On Illumos rm -rf / does nothing. POSIX says that removing / has undefined behavior, so the obviously smart (useful, user-friendly, GOOD) thing to do is to do nothing, as that fits "undefined behavior".

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That's quite funny... but ultimately futile. It doesn't say what happens if you say "DROP TABLE xyz<ENTER>WHERE...ohshit". (The <ENTER> bit is because you're used to doing that in your preferred SQL-DB editor.)

One should NEVER do anything non-scripted on a production system. ALWAYS enter it into a file and then do the "run-sql-from-a-file" command.

EDIT: Yes, I also realize that "rm -rf /" can theoretically happen if you have a bad variable substitution, but you MUST turn on the flags that cause your shell to error out instead of just substituting the empty string.

Protecting against every damned footgun is not possible. But some footguns blow users' feet off so often (this one because shell scripting is so tricky and dangerous) that it's est to do something about it.

Indeed not, but just having the extra step of "write this into a file" (and perhaps have someone look it over) catches most of those really bad mistakes.

It's really about NOT getting into the habit of "just fix it in production". That way lies madness.

If you work interactively you can use tab completion which takes care of most typos. That's something you don't have in scripts.

It's actually required by POSIX to do nothing:

If either of the files dot or dot-dot are specified as the basename portion of an operand (that is, the final pathname component) or if an operand resolves to the root directory, rm shall write a diagnostic message to standard error and do nothing more with such operands.

Source: http://pubs.opengroup.org/onlinepubs/9699919799/utilities/rm...

rm -rf /* ?

I believe the spec says arguments can be deleted in any order, so it always chooses "current directory” first, which fails, failing the whole command

Correct.

No, doesn’t work like that, meaning it should actually delete everything. The shell is expanding /* to the list of paths, not rm, and /* does not expand to / at all.

Try adding “echo “ in front of the rm command line to see how it expands. (That, by the way, is often a good idea.)

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