postgres：无法识别的服务

读完这个问题后，我做了：

gsamaras@gsamaras:~$ sudo apt-get install postgresql
Reading package lists... Done
Building dependency tree       
Reading state information... Done
postgresql is already the newest version.
The following packages were automatically installed and are no longer required:
  account-plugin-windows-live asymptote asymptote-doc freeglut3 gdebi-core
  gksu latex-beamer latex-xcolor libgksu2-0 libgsl0ldbl liblouis-data
  liblouis2 libpoppler-qt4-4 libsigsegv2 libupstart1 linux-headers-3.16.0-30
  linux-headers-3.16.0-30-generic linux-headers-3.16.0-40
  linux-headers-3.16.0-40-generic linux-image-3.16.0-30-generic
  linux-image-3.16.0-40-generic linux-image-extra-3.16.0-30-generic
  linux-image-extra-3.16.0-40-generic pgf preview-latex-style prosper ps2eps
  python-imaging-tk python3-brlapi python3-louis python3-pyatspi
  python3-speechd texlive-extra-utils texlive-font-utils
  texlive-generic-recommended texlive-lang-english texlive-latex-extra
  texlive-latex-extra-doc texlive-latex-recommended
  texlive-latex-recommended-doc texlive-pictures texlive-pictures-doc
  texlive-pstricks texlive-pstricks-doc texmaker-data
Use 'apt-get autoremove' to remove them.
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
gsamaras@gsamaras:~$ sudo service postgres restart
postgres: unrecognized service
gsamaras@gsamaras:~$ sudo apt-get install postgresql-server
Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package postgresql-server is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package 'postgresql-server' has no installation candidate

任何想法？