/tmp and other temporary directories and files are now managed by systemd and are not tmpfs. sytemd-tmpfiles gives to the user the ability to choose what they want to do with temporary directories/files. There are a ton of options that the user can choose from and everything is managed though config files (see man tmpfiles.d).

Create a temporary directory in your HOME folder

Using the global /tmp directory can be security issue as anyone can read this directory. If the user is not very carefull with the permissions they set on their files, confidential information might leak. Also, programs packaged with snap cannot access the global temporary directory /tmp by default.

To create a temporary directory in your HOME, write a config file like this one in $HOME/.config/user-tmpfiles.d/tmp.conf:

# Delete the content of ~/tmp on reboot
D %h/tmp 0750 - - -

and enable the following user service:

systemctl --user enable systemd-tmpfiles-setup.service

Now everytime the user login, $HOME/tmp will be cleaned (or created if needed). For the config to take effect immediately, you can run systemd-tmpfiles --user --create to create the directory and systemd-tmpfiles --user --remove to cleanup the directory.

If you don’t like to see your Downloads becoming more of a mess day after day, you can also create the following rule:

e %h/Downloads 0755 - - 30d

Then, files older than 30 days will be removed automatically.