This chapter outlines the interaction between Postgres and the operating system. All Postgres commands that are executed directly from a Unix shell are found in the directory .../bin. Including this directory in your search path will make executing the commands easier. A collection of system catalogs exist at each site. These include a class (pg_user) that contains an instance for each valid Postgres user. The instance specifies a set of Postgres privileges, such as the ability to act as Postgres super-user, the ability to create/destroy databases, and the ability to update the system catalogs. A Unix user cannot do anything with Postgres until an appropriate instance is installed in this class. Further information on the system catalogs is available by running queries on the appropriate classes.

shows how the Postgres distribution is laid out when installed in the default way. For simplicity, we will assume that Postgres has been installed in the directory /usr/local/pgsql. Therefore, wherever you see the directory /usr/local/pgsql you should substitute the name of the directory where Postgres is actually installed. All Postgres commands are installed in the directory /usr/local/pgsql/bin. Therefore, you should add this directory to your shell command path. If you use a variant of the Berkeley C shell, such as csh or tcsh, you would add set path = ( /usr/local/pgsql/bin path ) in the .login file in your home directory. If you use a variant of the Bourne shell, such as sh, ksh, or bash, then you would add PATH=/usr/local/pgsql/bin PATH export PATH to the .profile file in your home directory. From now on, we will assume that you have added the Postgres bin directory to your path. In addition, we will make frequent reference to "setting a shell variable" or "setting an environment variable" throughout this document. If you did not fully understand the last paragraph on modifying your search path, you should consult the UNIX manual pages that describe your shell before going any further. If you have not set things up in the default way, you may have some more work to do. For example, if the database server machine is a remote machine, you will need to set the PGHOST environment variable to the name of the database server machine. The environment variable PGPORT may also have to be set. The bottom line is this: if you try to start an application program and it complains that it cannot connect to the postmaster, you must go back and make sure that your environment is properly set up.