> There should be per-user temporary directories. In fact, on modern systems there are per-user temporary directories!
On Linux+systemd, I think this is referring to /run/user/$UID. $XDG_RUNTIME_DIR is set to this path in a session by default. There's a spec for that environment variable at <https://specifications.freedesktop.org/basedir-spec/latest/>. I assume there's also some systemd doc talking about this.
On macOS, I see that $TMPDIR points to a path like /var/folders/jd/d94zfh8d1p3bv_q56wmlxn6w0000gq/T/ that appears to be per-user also.
What do FreeBSD/OpenBSD/NetBSD do?
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