How to fix PostgreSQL installation
You need to increase the maximum size of a chunk of shared memory Linux kernel allows to allocate at once (known as SHMMAX parameter)
You need to edit /etc/sysctl.conf
and add the following line:
kernel.shmmax = 41943040
(where 41943040
is the size of memory in bytes, i.e. 40 megabytes. On production system you probably want to set this value way higher - Postgres documentation recommends to start with 1/4 of available memory)
Then run
sudo sysctl -p
and restart postgres again.
Alternatively, you can edit /etc/postgresql/<version>/main/postgresql.conf
and reduce the value of shared_buffers
parameter.
This is a bug, more info here
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/264336
(there's also /etc/sysctl.d/30-postgresql-shm.conf
file which is supposed to be used for this purpose but it doesn't seem to be included from the main config so editing it has no effect)