Comment by woodruffw
4 years ago
Genuine question: on what systems is `/tmp` persistent? Both macOS and Ubuntu 20.04 clear `/tmp` on every reboot for me, and I haven't changed the defaults at all.
4 years ago
Genuine question: on what systems is `/tmp` persistent? Both macOS and Ubuntu 20.04 clear `/tmp` on every reboot for me, and I haven't changed the defaults at all.
Right, /var/tmp is the "Persistent Temp" directory, and /tmp is "Ephemeral Temp". The /run directory is for runtime data such as PID files, Unix sockets, named FIFOs, and generated systemd units—it has a specific internal structure and shouldn't be used as a direct alternative to the relatively unstructured /tmp directory. While both are generally ephemeral tmpfs mounts, only /tmp is writable to all users.
"Persistent Temp" should be /var/tmp. "Persistent Temp" is also an oxymoron.
> "Persistent Temp" is also an oxymoron.
It's not an oxymoron to have files which are temporary but not limited in scope to a single power cycle. For example, you could have a long-running process which you want to be able to resume if it's interrupted; /var/tmp would be an appropriate place for the state. The data is temporary because it will be deleted once the process is finished, but you wouldn't want it wiped out by a system reset. Generally /tmp is cleared at every reset, and is often a tmpfs mount, while files in /var/tmp are automatically cleaned up only when they reach a certain age.
Except that the FHS says that "data stored in /var/tmp is typically deleted in a site-specific manner", and as an application vendor you have no control over that site-specific clean frequency. On all my systems, /var/tmp is a symlink to /tmp and that has never caused any issue.
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Basically no one uses /var/tmp for anything (and nobody should either). World writable directories are a mistake and only continue to exist because apps assume they are available.
/tmp and friends are poorly named. They really should be /shared or /dmz or /freeforall or something.
* If you need service-specific tmp space use RuntimeDirectory or PrivateTmp if your app is hardcoded to /tmp.
* If you need service-specific persistent data that goes in /var/lib/your-app.
* If you need temp space for your user it's at /var/run/user/your-uid.
* If you need more than one user/service to share files but not everyone then god have mercy on your soul because all options are bad. There sure are a lot of them but none of them are at all satisfying.
> Basically no one uses /var/tmp for anything
Gentoo does, at least by default: https://wiki.gentoo.org/wiki//etc/portage/make.conf#PORTAGE_...
All storage is temporary. You just gotta wait long enough.
People don't reboot often. Persistent tmp basically means it will be cleared in an infrequent manner, so the likelihood of it going away 1s after you release your file handle is low.