Server crashed, now cannot start postgres

   Tried to compile 3 large programs at one time and the CPU overheated,
shutting down the server. Now when I try to start postgres-9.5.4 (as the
superuser, postgres) I get this result:

postgres@salmo:~$ postgres -D /var/lib/pgsql/9.5/data/ &
[1] 14544
postgres@salmo:~$ FATAL:  could not open shared memory segment
"/PostgreSQL.1804289383": Permission denied

   Not before encountering this problem I've no idea where to look to see how
to fix it. Please advise.

TIA,

Rich