não pôde se conectar ao servidor: Nenhum arquivo ou diretório no PostgreSQL

Question

Eu tenho um VPS com o Ubuntu 14.04.5 LTS (GNU / Linux 2.6.32-042stab127.2 x86_64) e também tenho o Postgresql instalado. Estou usando o Postgresql em um aplicativo Ruby on Rails. De repente meu aplicativo parou de funcionar jogando o erro

could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

    $psql -V 
     psql (PostgreSQL) 11.0 (Ubuntu 11.0-1.pgdg14.04+2)

    $pg_config --version
      PostgreSQL 11.0 (Ubuntu 11.0-1.pgdg14.04+2)

    $postgres -V
     The program 'postgres' is currently not installed. You can install it by typing:
     apt-get install postgres-xc

   $locate bin/postgres
    /usr/lib/postgresql/11/bin/postgres
    /usr/lib/postgresql/9.3/bin/postgres
    /usr/lib/postgresql/9.4/bin/postgres
    /usr/lib/postgresql/9.5/bin/postgres

  $/usr/lib/postgresql/11/bin/postgres -V
    postgres (PostgreSQL) 11.0 (Ubuntu 11.0-1.pgdg14.04+2)

  $pg_lsclusters
  9.3 main    5432 down   postgres /var/lib/postgresql/9.3/main /var/log/postgresql/postgresql-9.3-main.log
  11  main    5433 down   postgres /var/lib/postgresql/11/main  /var/log/postgresql/postgresql-11-main.log

O status do postgres está baixo

 $service postgresql status
 9.3/main (port 5432): down
 11/main (port 5433): down

 $systemctl status postgresql.service

  postgresql.service
  Loaded: error (Reason: No such file or directory)
 Active: inactive (dead)

 $systemctl status [email protected]

   [email protected]
   Loaded: error (Reason: No such file or directory)
   Active: inactive (dead)

$grep -H '^port' /etc/postgresql/*/main/postgresql.conf /etc/postgresql/11/main/postgresql.conf:port = 5433
/etc/postgresql/9.3/main/postgresql.conf:port = 5432

Estou tentando iniciar o Postgresql 9.3 com

 $service postgresql start 9.3
    * Starting PostgreSQL 9.3 database server                                                                                          
    * Failed to issue method call: Unit [email protected] failed 
     to load: No such file or directory. See system logs and 'systemctl 
     status [email protected]' for details.


  $sudo systemctl start postgresql
   Failed to issue method call: Unit postgresql.service failed to load: No 
   such file or directory. See system logs and 'systemctl status 
    postgresql.service' for details.


   $/etc/init.d# /etc/init.d/postgresql start
    * Starting PostgreSQL 11 database server                                                                                           
    * Failed to issue method call: Unit [email protected] failed to 
    load: No such file or directory. See system logs and 'systemctl status 
    [email protected]' for details.

    [fail]
   * Starting PostgreSQL 9.3 database server                                                                                          
   * Failed to issue method call: Unit [email protected] failed to 
    load: No such file or directory. See system logs and 'systemctl status 
    [email protected]' for details.
    [fail]

Não consigo iniciar o PostgreSQL. Não entendo por que caiu de repente, estava funcionando bem até ontem.