could not bind IPv4 socket: Permission denied - postgresql

Question

I am trying to set up a new instance of PostgreSQL 9.6 on a machine. I have tested it on another machine and its working fine on that machine. But the same process is not working on new machine. Below are the steps I am using
created a new data directory with below command
/opt/rh/rh-postgresql96/root/bin/initdb -D /var/lib/pgsql/9.6/data/
created a service file /etc/systemd/system/rh-postgresql96-inst2.service with below content
.include /lib/systemd/system/rh-postgresql96-postgresql.service
[Service]
Environment=PGDATA=/var/lib/pgsql/9.6/data/
Environment=PGPORT=5433
User=postgres
Group=root
registered service using command systemctl enable rh-postgresql96-inst2
now using command systemctl start rh-postgresql96-inst2 to start service.
All these steps are working fine on one machine but not on the 2nd one.
I am getting below error while starting service on the 2nd machine
rh-postgresql96-inst2.service - PostgreSQL database server
Loaded: loaded (/etc/systemd/system/rh-postgresql96-inst2.service; enabled; vendor preset: disabled)
Active: failed (Result: exit-code) since Mon 2018-06-18 09:59:01 UTC; 10s ago
Process: 7552 ExecStart=/opt/rh/rh-postgresql96/root/usr/libexec/postgresql-ctl start -D ${PGDATA} -s -w -t ${PGSTARTTIMEOUT} (code=exited, status=1/FAILURE)
Process: 7550 ExecStartPre=/opt/rh/rh-postgresql96/root/usr/libexec/postgresql-check-db-dir %N (code=exited, status=0/SUCCESS)
HINT: Is another postmaster already running on port 5433? If not, wait a few seconds and retry.
LOG: could not bind IPv4 socket: Permission denied
HINT: Is another postmaster already running on port 5433? If not, wait a few seconds and retry.
WARNING: could not create listen socket for "localhost"
FATAL: could not create any TCP/IP sockets
LOG: database system is shut down
systemd[1]: rh-postgresql96-inst2.service: control process exited, code=exited status=1
systemd[1]: Failed to start PostgreSQL database server.
systemd[1]: Unit rh-postgresql96-inst2.service entered failed state.
systemd[1]: rh-postgresql96-inst2.service failed.
However, I am able to start service using pg_ctl.
Also, I have checked with netstat, lsof command to check if any other postgresql instance is running on port 5433 but its not the case.
Infact i tried 5431, 5434 ports also but server is not starting up

Answer 1

Instead of turning of SELinux you should allow postgres to bind to port 5433 in SELinux.
There is a port parameter postgresql_port_t which by default has port 5432 and 9898.
semanage port -l | grep post
postgresql_port_t tcp 5433, 9898
What you could do is simply add port 5433 to this list.
semanage port -a -t postgresql_port_t 5433 -p tcp
semanage port -l | grep post
postgresql_port_t tcp 5433, 5432, 9898
After that you can start your postgres server listening on port 5433
systemctl enable rh-postgresql96-postgresql
systemctl start rh-postgresql96-postgresql
netstat -tulpn
tcp 0 0 127.0.0.1:5432 0.0.0.0:* LISTEN 2847/postgres
tcp 0 0 127.0.0.1:5433 0.0.0.0:* LISTEN 2775/postgres
There is also a handy tool called audit2allow to help debug selinux problems.
audit2allow -m whatiswrong < /var/log/audit/audit.log > /root/showme.te
The file showme.te show you why SELinux is not allowing the service to do what you need.
You should not turn off SELinux just because it's hard to understand or if you don't know how it works. Instead you should study it :)
I reccomend this lecture from the Red Hat Summit https://www.redhat.com/en/about/videos/summit-2018-security-enhanced-linux-mere-mortals

Answer 2

This issue was related to SELinux.
When I run command sestatus on both machines, output was a little bit different.
One server had Current mode: permissive and 2nd one had Current mode: enforcing.
So I changed the current mode to permissive on the 2nd machine using command setenforce 0.
and it resolved the permission related issue. Now I am able to start 2nd instance.