systemd-remount-fs.service, systemd-remount-fs — Remount root and kernel file systems
systemd-remount-fs.service
/usr/lib/systemd/systemd-remount-fs
systemd-remount-fs.service
                is an early-boot service that applies mount options
                listed in
                fstab(5)
                to the root file system, the /usr
                file system and the kernel API file systems. This is
                required so that the mount options of these file
                systems -- which are pre-mounted by the kernel, the
                initial RAM disk, container environments or system
                manager code -- are updated to those listed in
                /etc/fstab. This service ignores
                normal file systems and only changes the root file
                system (i.e. /),
                /usr and the virtual kernel API
                file systems such as /proc,
                /sys or
                /dev. This service executes no
                operation if /etc/fstab does not
                exist or lists no entries for the mentioned file
                systems.
For a longer discussion of kernel API file systems see API File Systems.