In the previous sections, you have seen how to install PostgreSQL and connect to it, but we have not looked at the storage part of a cluster. Since the aim of PostgreSQL, as well as the aim of any relational database, is to permanently store data, the cluster needs some sort of permanent storage. In particular, PostgreSQL exploits the underlying filesystem to store its own data. All of the PostgreSQL-related stuff is contained in a directory known as PGDATA.
The PGDATA directory acts as the disk container that stores all the data of the cluster, including the users' data and cluster configuration.
The following is an example of the content of PGDATA for a running PostgreSQL 12 cluster (it looks the same for a PostgreSQL 13 instance):
$ sudo ls -1 /postgres/12
PG_VERSION
base
global
pg_commit_ts
pg_dynshmem
pg_hba.conf
pg_ident.conf
pg_logical
pg_multixact
pg_notify
pg_replslot
pg_serial
pg_snapshots
pg_stat
pg_stat_tmp
pg_subtrans
pg_tblspc
pg_twophase
pg_wal
pg_xact...
