>>> telnet 127.0.0.1 5432
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
Connection closed by foreign host.

>>> sudo iptables -L
Chain INPUT (policy ACCEPT)
target     prot opt source               destination

Chain FORWARD (policy ACCEPT)
target     prot opt source               destination

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             all                     md5
# IPv6 local connections:
host    all             all             ::1/128                 md5
# Allow replication connections from localhost, by a user with the
# replication privilege.
local   replication     all                                     peer
host    replication     all             127.0.0.1/32            md5
host    replication     all             ::1/128                 md5

# PostgreSQL configuration file

#------------------------------------------------------------------------------
# FILE LOCATIONS
#------------------------------------------------------------------------------

# The default values of these variables are driven from the -D command-line
# option or PGDATA environment variable, represented here as ConfigDir.

data_directory = '/var/lib/postgresql/12/main'          # use data in another directory
                                        # (change requires restart)
hba_file = '/etc/postgresql/12/main/pg_hba.conf'        # host-based authentication file
                                        # (change requires restart)
ident_file = '/etc/postgresql/12/main/pg_ident.conf'    # ident configuration file
                                        # (change requires restart)

# If external_pid_file is not explicitly set, no extra PID file is written.
external_pid_file = '/var/run/postgresql/12-main.pid'                   # write an extra PID file
                                        # (change requires restart)


#------------------------------------------------------------------------------
# CONNECTIONS AND AUTHENTICATION
#------------------------------------------------------------------------------

# - Connection Settings -

listen_addresses = '*'                  # what IP address(es) to listen on;
                                        # comma-separated list of addresses;
                                        # defaults to 'localhost'; use '*' for all
                                        # (change requires restart)
port = 5432                             # (change requires restart)
max_connections = 100                   # (change requires restart)
#superuser_reserved_connections = 3     # (change requires restart)
unix_socket_directories = '/var/run/postgresql' # comma-separated list of directories
                                        # (change requires restart)


# - Authentication -

authentication_timeout = 5s
password_encryption = md5               # md5 or scram-sha-256
#db_user_namespace = off

# - SSL -

ssl = on
#ssl_ca_file = ''
ssl_cert_file = '/etc/ssl/certs/ssl-cert-snakeoil.pem'
#ssl_crl_file = ''
ssl_key_file = '/etc/ssl/private/ssl-cert-snakeoil.key'

#------------------------------------------------------------------------------
# RESOURCE USAGE (except WAL)
#------------------------------------------------------------------------------

# - Memory -

shared_buffers = 128MB                  # min 128kB
                                        # (change requires restart)

dynamic_shared_memory_type = posix      # the default is the first option
                                        # supported by the operating system:
                                        #   posix
                                        #   sysv
                                        #   windows
                                        #   mmap
                                        # (change requires restart)

#------------------------------------------------------------------------------
# WRITE-AHEAD LOG
#------------------------------------------------------------------------------

# - Checkpoints -

max_wal_size = 1GB
min_wal_size = 80MB

# - Archiving -

/mnt/server/archivedir/%f'

#------------------------------------------------------------------------------
# REPORTING AND LOGGING
#------------------------------------------------------------------------------

# - What to Log -

log_line_prefix = '%m [%p] %q%u@%d '            # special values:
                             
log_timezone = 'Etc/UTC'

#------------------------------------------------------------------------------
# PROCESS TITLE
#------------------------------------------------------------------------------

cluster_name = '12/main'                        # added to process titles if nonempty
                                  
#------------------------------------------------------------------------------
# CLIENT CONNECTION DEFAULTS
#------------------------------------------------------------------------------

# - Locale and Formatting -

datestyle = 'iso, mdy'
#intervalstyle = 'postgres'
timezone = 'Etc/UTC'


# These settings are initialized by initdb, but they can be changed.
lc_messages = 'C.UTF-8'                 # locale for system error message
                                        # strings
lc_monetary = 'C.UTF-8'                 # locale for monetary formatting
lc_numeric = 'C.UTF-8'                  # locale for number formatting
lc_time = 'C.UTF-8'                             # locale for time formatting

# default configuration for text search
default_text_search_config = 'pg_catalog.english'



include_dir = 'conf.d'                  # include files ending in '.conf' from