在尝试安装ambari2.4时，我得到以下错误。

root@ishanNode1:~# apt-get install ambari-server 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
ambari-server : Depends: postgresql (>= 8.1) but it is not going to be       installed
E: Unable to correct problems, you have held broken packages.

我已经安装了postgresql，因为它不是在ubuntu中默认安装的

root@ishanNode1:~# service postgresql status
● postgresql.service - PostgreSQL RDBMS
Loaded: loaded (/lib/systemd/system/postgresql.service; disabled; vendor  preset: enabled)
Active: active (exited) since Fri 2018-02-16 00:01:58 IST; 16s ago
Process: 5847 ExecStart=/bin/true (code=exited, status=0/SUCCESS)
Main PID: 5847 (code=exited, status=0/SUCCESS)

Feb 16 00:01:58 ishanNode1 systemd[1]: Starting PostgreSQL RDBMS...
Feb 16 00:01:58 ishanNode1 systemd[1]: Started PostgreSQL RDBMS.

请告诉我怎么修。