[adrian_b]

While tmpfs can be very useful even as it is, users must beware that copying a file from another Linux file system to tmpfs can lose a part of the file metadata, without giving any warnings or errors.

The main problem is that copying a file to tmpfs will drop extended attributes. Old versions of tmpfs dropped all extended attributes, modern versions of tmpfs keep some security-related extended attributes, but they still drop any user-defined extended attributes.

Old versions of tmpfs truncated some high-resolution timestamps, e.g. those coming from xfs, but I do not know if this still happens on modern versions of tmpfs.

Before learning these facts, I could not understand while some file copies lost parts of their metadata, after being copied via /tmp between 2 different users, on a multi-user computer where /tmp was mounted on tmpfs.

Now that I know, when I have to copy a file via tmpfs, I have to make a pax archive, which preserves file metadata. Older tar archive formats may have the same problems like tmpfs.