Ruby: Could not find a temporary directory

Question

I am getting some 500 errors in my Passenger Rails app. When looking at the log it appears passenger cannot access the /tmp dir. I have validated that it is there and has

Answer 1

The most significant part of the stack trace is the error message:

could not find a temporary directory (ArgumentError)

When you tell Ruby >= 2.0 to create a temporary file, it looks for a directory where it can create a file in a secure way. Creating a temporary files in a directory where anybody can replace the file while you are working on it would be a big (and common) security hole!

You have two possibilites:

• Tell ruby where it can securely create temporary files by setting one of the environment variables TMPDIR or TMP or TEMP to a directory that is secure.

• Fix up the permissions on a directory that ruby tries to use anyway. Directories that Ruby tries to use anyway: systempdir ("/tmp") and the current directory

Ruby deems a directory secure if the directory is either not world writeable or has the sticky bit set. (Do not confuse the sticky bit (t) with the seteuid/setgid bit (s)!)

So instead of setting TMPDIR, you might either make your working directory not world writable or do:

chmod +t /tmp

The manual page of chmod explains the use of the sticky bit:

[It] prevents unprivileged users from removing or renaming a file in the directory unless they own the file or the directory; this is called the restricted deletion flag for the directory, and is commonly found on world-writable directories like /tmp.

Here is what can happen without the sticky bit: https://security.stackexchange.com/questions/9115/can-you-describe-a-real-life-scenario-of-exploiting-sticky-bits/108666#108666

See also: https://blog.diacode.com/fixing-temporary-dir-problems-with-ruby-2