Docker daemon can't starting after system reboot
I solved my problem.
I had SocketGroup=docker configuration in /usr/lib/systemd/system/docker.socket file, but at Docker startup time a group docker did not exist because I manage my Linux identities (users, groups, etc) with FreeIPA and this starts after Docker.
Solution
Add this line to /etc/group file:
docker:x:GID:
GID is a same number as is configured in FreeIPA for group docker.