Is there a tool to generate ERD diagram for PostgresQL especially for PgAdmin under Linux?

DbVisualizer is a Java Swing app which can generate relation graphs from any JDBC source (including PostgreSQL). I've found the best way to view the generated graph (after you have found a layout you like) is to print it to PDF and use Preview.app to view the result. The built-in view is somewhat lacking.

There are also a few Graphviz options around including AutoDocTry Aqua Data Studio http://www.aquafold.com/downloads.htmlYou can also try out SQL*Power Architect

ERMaster is free GUI editor for ER diagrams and runs as Eclipse plugin. It has a feature to create ER diagram by importing tables from existing database. It supports several databases (MySQL, Oracle, DB2, PostgresSQL, HSQLDB, SQLITE, SQLServer)

Try SchemaSpy, it does a good result for PostgreSQL including some of meta-data as commentsSchemaCrawler for PostgreSQL is a command-line tool that can generate database diagrams from a PostgreSQL database. It is free and open-source.