Nothing can happen to a database unless the postmaster process is running. As the site administrator, there are a number of things you should remember before starting the postmaster. These are discussed in the installation and configuration sections of this manual. However, if Postgres has been installed by following the installation instructions exactly as written, the following simple command is all you should need to start the postmaster: % postmaster The postmaster occasionally prints out messages which are often helpful during troubleshooting. If you wish to view debugging messages from the postmaster, you can start it with the -d option and redirect the output to the log file: % postmaster -d >& pm.log & If you do not wish to see these messages, you can type % postmaster -S and the postmaster will be "S"ilent. Notice that there is no ampersand ("&") at the end of the last example. createuser enables specific users to access Postgres. destroyuser removes users and prevents them from accessing Postgres. Note that these commands only affect users with respect to Postgres; they have no effect on users other privileges or status with regards to the underlying operating system. It is possible to create a database in a location other than the default location for the installation. Remember that all database access actually occurs through the database backend, so that any location specified must be accessible by the backend. Alternate database locations are created and referenced by an environment variable which gives the absolute path to the intended storage location. This environment variable must have been defined before the backend was started and must be writable by the postgres administrator account. Any valid environment variable name may be used to reference an alternate location, although using variable name with a prefix of PGDATA is recommended to avoid confusion and conflict with other variables. In previous versions of Postgres, it was also permissable to use an absolute path name to specify an alternate storage location. The environment variable style of specification is to be preferred since it allows the site administrator more flexibility in managing disk storage. If you prefer using absolute paths, you may do so by defining "ALLOW_ABSOLUTE_DBPATHS" and recompiling Postgres To do this, either add this line #define ALLOW_ABSOLUTE_DBPATHS 1 to the file src/include/config.h, or by specifying CFLAGS+= -DALLOW_ABSOLUTE_DBPATHS in your Makefile.custom. Remember that database creation is actually performed by the database backend. Therefore, any environment variable specifying an alternate location must have been defined before the backend was started. To define an alternate location PGDATA2 pointing to /home/postgres/data, first type % setenv PGDATA2 /home/postgres/data to define the environment variable to be used with subsequent commands. Usually, you will want to define this variable in the Postgres superuser's .profile or .cshrc initialization file to ensure that it is defined upon system startup. Any environment variable can be used to reference alternate location, although it is preferred that the variables be prefixed with "PGDATA" to eliminate confusion and the possibility of conflicting with or overwriting other variables. To create a data storage area in PGDATA2, ensure that /home/postgres already exists and is writable by the postgres administrator. Then from the command line, type % setenv PGDATA2 /home/postgres/data % initlocation $PGDATA2 Creating Postgres database system directory /home/postgres/data Creating Postgres database system directory /home/postgres/data/base To test the new location, create a database test by typing % createdb -D PGDATA2 test % destroydb test Assuming that your site administrator has properly started the postmaster process and authorized you to use the database, you (as a user) may begin to start up applications. As previously mentioned, you should add /usr/local/pgsql/bin to your shell search path. In most cases, this is all you should have to do in terms of preparation. If you get the following error message from a Postgres command (such as psql or createdb): connectDB() failed: Is the postmaster running at 'localhost' on port '5432'? it is usually because either the postmaster is not running, or you are attempting to connect to the wrong server host. If you get the following error message: FATAL 1:Feb 17 23:19:55:process userid (2360) != database owner (268) it means that the site administrator started the postmaster as the wrong user. Tell him to restart it as the Postgres superuser. Now that Postgres is up and running we can create some databases to experiment with. Here, we describe the basic commands for managing a database. Let's say you want to create a database named mydb. You can do this with the following command: % createdb mydb Postgres allows you to create any number of databases at a given site and you automatically become the database administrator of the database you just created. Database names must have an alphabetic first character and are limited to 16 characters in length. Not every user has authorization to become a database administrator. If Postgres refuses to create databases for you, then the site administrator needs to grant you permission to create databases. Consult your site administrator if this occurs. Once you have constructed a database, you can access it by: running the Postgres terminal monitor program (psql) which allows you to interactively enter, edit, and execute SQL commands. writing a C program using the libpq subroutine library. This allows you to submit SQL commands from C and get answers and status messages back to your program. This interface is discussed further in the PostgreSQL Programmer's Guide. You might want to start up psql, to try out the examples in this manual. It can be activated for the mydb database by typing the command: % psql mydb You will be greeted with the following message: Welcome to the Postgres interactive sql monitor: type \? for help on slash commands type \q to quit type \g or terminate with semicolon to execute query You are currently connected to the database: mydb mydb=> This prompt indicates that the terminal monitor is listening to you and that you can type SQL queries into a workspace maintained by the terminal monitor. The psql program responds to escape codes that begin with the backslash character, "\". For example, you can get help on the syntax of various Postgres SQL commands by typing: mydb=> \h Once you have finished entering your queries into the workspace, you can pass the contents of the workspace to the Postgres server by typing: mydb=> \g This tells the server to process the query. If you terminate your query with a semicolon, the backslash-g is not necessary. psql will automatically process semicolon terminated queries. To read queries from a file, say myFile, instead of entering them interactively, type: mydb=> \i fileName To get out of psql and return to UNIX, type mydb=> \q and psql will quit and return you to your command shell. (For more escape codes, type backslash-h at the monitor prompt.) White space (i.e., spaces, tabs and newlines) may be used freely in SQL queries. Single-line comments are denoted by --. Everything after the dashes up to the end of the line is ignored. Multiple-line comments, and comments within a line, are denoted by /* ... */ If you are the database administrator for the database mydb, you can destroy it using the following UNIX command: % destroydb mydb This action physically removes all of the UNIX files associated with the database and cannot be undone, so this should only be done with a great deal of forethought.