Postgresql Failed to start on linux - linux

Question

My PostgreSQL stopped working suddenly and I am unable to start it. (Last changes in my Linux were, I tried to install dockers).
When I run the command:
sudo service postgresql restart
OR
sudo service postgresql start
I get the error:
* Starting PostgreSQL 11 database server
* Failed to issue method call: Unit postgresql#11-main.service failed to load: No such file or directory. See system logs and 'systemctl status postgresql#11-main.service' for details.
[fail]
and
~$ sudo service postgresql status
11/main (port 5434): down
There result of systemctl status:
~ $ sudo systemctl status postgresql#11-main.service
postgresql#11-main.service
Loaded: error (Reason: No such file or directory)
Active: inactive (dead)
I have tried all the available options on SO and on other forums but neither worked for me.
What can be the issue?
EDIT:
cat /etc/os-release
Output:
NAME="Ubuntu"
VERSION="14.04.6 LTS, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04.6 LTS"
VERSION_ID="14.04"
HOME_URL="http://www.ubuntu.com/"
SUPPORT_URL="http://help.ubuntu.com/"
BUG_REPORT_URL="http://bugs.launchpad.net/ubuntu/"
and
ls -al /var/lib/pgsql
output:
ls: cannot access /var/lib/pgsql: No such file or directory
Then I tried
ls -al /var/lib/postgresql/
output:
total 40
drwxr-xr-x 7 postgres postgres 4096 Mar 24 13:34 .
drwxr-xr-x 90 root root 4096 Apr 6 18:36 ..
drwxr-xr-x 4 postgres postgres 4096 Apr 6 18:20 11
drwxr-xr-x 3 postgres postgres 4096 Feb 11 2016 9.3
drwxr-xr-x 3 postgres postgres 4096 Dec 3 2018 9.4
drwx------ 2 postgres postgres 4096 Jan 31 11:20 .aptitude
-rw------- 1 postgres postgres 5898 Apr 6 18:33 .bash_history
drwx------ 3 postgres postgres 4096 Feb 11 2016 .cache
-rw------- 1 postgres postgres 2180 Mar 24 13:34 .psql_history
and
yum info postgresql11-server
Error: No matching Packages to list
EDIT 2
sudo systemctl list-unit-files | grep postg et
output:
grep: et: No such file or directory
and
ls -l /var/lib/postgresql/11
output:
total 8
drwxr-xr-x 2 root root 4096 Apr 6 18:20 data
drwx------ 19 postgres postgres 4096 Apr 2 18:53 main