Unable to change PostgreSQL admin password or log in to PostgreSQL on Plesk: psql: FATAL: Ident authentication failed for user “postgres”

Symptoms

• Unable to update PostgreSQL password via command line:

  # plesk bin database-server –update-server localhost:5432 -type postgresql -passwd ‘<password>’
  psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket “/tmp/.s.PGSQL.5432”?
  psql: FATAL: Ident authentication failed for user “postgres”
  psql: could not connect to server: No such file or directory Is the server running locally and accepting connections on Unix domain socket “/tmp/.s.PGSQL.5432”?

• It is not possible to log in to the PostgreSQL server:

  # psql -Uadmin postgres
  Password for user admin:
  psql: FATAL: password authentication failed for user “postgres”

Cause

Incorrect authentication method (ident) configured on PostgreSQL.

Resolution

1. Connect to the server via SSH.

2. Edit file /var/lib/pgsql/data/pg_hba.conf, replacing ident to trust in the section beginning with “local”, as follows:

   # TYPE DATABASE USER CIDR-ADDRESS METHOD
    # "local" is for Unix domain socket connections only 
    local all all trust
    # IPv4 local connections: 
    host all all 127.0.0.1/32 trust 
    # IPv6 local connections: 
    host all all ::1/128 trust

3. In case the following line exists, remove it:

   host all all 0.0.0.0/0 md5

4. Restart PostgreSQL server:

   # service postgresql restart