There is no "mount" session in Posix.
Where can it be specified ?
Is there a standard for kernel ?
Don't you read near the end of my previous post?
If the whole system (including all user data) is incorporated in SINGLE filesystem, (new writings hereafter) and if nothing other local optional filesystem is completely disallowed (POSIX wouldn't be prohibiting such an configuration) by the system developers and administrators, network access via protocols that does NOT require filesystem mounts (http, ftp, smtp,...) are allowed but anything requiring moutnts (NFS, SMB, Netware,...) are prohibited, mount / unmount is completely unnecessary.
So my current guess is "mount is out of scope on POSIX".
If you really mandated to research with 100% correctness (logical thinking is not at all sufficient for you), purchase whichever of de-jure standard, read it from the top to bottom, without overlooking any single character, figure, diagram,... and confirm there's any description about /etc/fstab or mount.
As ISO/IEC/IEEE 9945 is currently under developement for update (you can see a link to
Draft International Standard
ISO/IEC DIS 9945 in the page linked from my previous post) and IEEE version (also linked from my previous post) is already updated as 2024 version, you'd better preferring it.
Quite fortunately, you can purchase PDF version, no need to wait for arrival of printed standard.
