[lvm2] no devices after reboot

I was installing a Gentoo system on lvm partitions. While doing so, the system of the live USB stick froze and I had to reboot. However, no lvm devices where present in /dev even though I successfully displayed the volume group (vgdisplay) and the logical volumes (lvdisplay). The point is, that after the boot volume groups are deactivated so I had to activate them. I had this info from #gentoo IRC channel but was too dump to record it somewhere accessible because I had to shutdown my system to go home. It took me a good deal of time to find the solution again on the net but here it is:

vgchange --activate y vg_sata