Trouble with postgresql -

i have uploaded question hasn't been solved re-posting it.

i experiencing problem in installing postgresql on ubuntu 14.04. did was:

1. sudo su -
2. sudo apt-get install postgresql postgresql-contrib
3. update-rc.d postgresql enable
4. service postgresql start

doing #3, got:

    update-rc.d: warning:  start runlevel arguments (none) not match postgresql default-start values (2 3 4 5)     update-rc.d: warning:  stop runlevel arguments (none) not match postgresql default-stop values (0 1 6)     enabling system startup links /etc/init.d/postgresql ...     removing system startup links /etc/init.d/postgresql ...     /etc/rc0.d/k21postgresql     /etc/rc1.d/k21postgresql     /etc/rc2.d/s19postgresql     /etc/rc3.d/s19postgresql     /etc/rc4.d/s19postgresql     /etc/rc5.d/s19postgresql     /etc/rc6.d/k21postgresql     adding system startup /etc/init.d/postgresql ...     /etc/rc0.d/k21postgresql -> ../init.d/postgresql     /etc/rc1.d/k21postgresql -> ../init.d/postgresql     /etc/rc6.d/k21postgresql -> ../init.d/postgresql     /etc/rc2.d/s19postgresql -> ../init.d/postgresql     /etc/rc3.d/s19postgresql -> ../init.d/postgresql     /etc/rc4.d/s19postgresql -> ../init.d/postgresql     /etc/rc5.d/s19postgresql -> ../init.d/postgresql 

in doing #4, getting error:

    postgresql server failed start. please check log output:     2015-07-17 21:54:24 pht log:  not open secondary authentication file "@admins" "/etc/postgresql/9.3/main/admins": no such file or directory     2015-07-17 21:54:24 pht log:  not open secondary authentication file "@admins" "/etc/postgresql/9.3/main/admins": no such file or directory     2015-07-17 21:54:24 pht log:  not open secondary authentication file "@demodbs" "/etc/postgresql/9.3/main/demodbs": no such file or directory     2015-07-17 21:54:24 pht log:  end-of-line before authentication method     2015-07-17 21:54:24 pht context:  line 75 of configuration file "/etc/postgresql/9.3/main/pg_hba.conf"     2015-07-17 21:54:24 pht fatal:  not load pg_hba.conf 

i thought installed postgresql correctly. wrong?

i have solved problem following joop's advice in comment.

i have opened pg_hba.conf using sudo (without sudo, appears empty) commented out lines have @admins.