Don't download to tmpfs

[jimsynz]

On my Debian trixie machine /tmp is mounted on tmpfs meaning that sometimes downloading and extracting the Debian image runs out of space. This is easily avoided by setting TMPDIR=/var/tmp before running the flasher however not everyone is going to understand how to figure this out (I had to use strings on the binary before the source was available).

[per1234]

Thanks for your report @jimsynz.

I think your report can be separated into two distinct components:

• Report that the location used for storing files on the host is inappropriate in the case where the user is using tmpfs
• Request for an easy way for the user to configure an arbitrary location

The implementation of the latter is already planned, tracked (tangentially) here: #17

allow the user to specify, using a flag (for example --temp-dir), a different directory to download and/or extract the image.

However, we might still consider that the first component would only be resolved by using an appropriate default location. I am wondering about this though:

This is easily avoided by setting TMPDIR=/var/tmp

From what I can see from the codebase and some experiments, the TMPDIR environment variable is not used:

arduino-flasher-cli/updater/download_image.go

Lines 114 to 115 in fb5dcd7

	// Download the zip
	temp, err := GetTempDir("download-")

arduino-flasher-cli/updater/download_image.go

Lines 169 to 170 in fb5dcd7

	func GetTempDir(prefix string) (*paths.Path, error) {
	userCacheDir, err := os.UserCacheDir()

https://cs.opensource.google/go/go/+/refs/tags/go1.25.1:src/os/file.go;l=531-538

	default: // Unix
		dir = Getenv("XDG_CACHE_HOME")
		if dir == "" {
			dir = Getenv("HOME")
			if dir == "" {
				return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined")
			}
			dir += "/.cache"

So the location used by arduino-flasher-cli is determined by the XDG_CACHE_HOME environment variable, or by HOME as a fallback.

Perhaps on your system the TMPDIR environment variable is referenced in the definition of XDG_CACHE_HOME?

So I'm wondering if perhaps this is actually a matter of your system being misconfigured rather than arduino-flasher-cli? Does it make sense to configure the XDG_CACHE_HOME environment variable to a path on tmpfs?