path: root/doc/src/sgml/start-ag.sgml

<!--
-	This file currently contains several small chapters.
-	Each chapter should be split off into a separate source file...
-	- thomas 1998-02-24
-->

<Chapter Id="postmaster">
<Title>Starting <Application>postmaster</Application></Title>

<Para>
     Nothing can happen to a database unless the
  <Application>postmaster</Application>
     process  is  running.  As the site administrator, there
     are a number  of  things  you  should  remember  before
     starting  the  <Application>postmaster</Application>.   
These are discussed in the installation and configuration sections
of this manual.
     However, if <ProductName>Postgres</ProductName> has been installed by following 
     the installation instructions exactly  as  written,  the  
     following  simple  command is all you should
     need to start the <Application>postmaster</Application>:
<ProgramListing>
% postmaster
</ProgramListing>
     The <Application>postmaster</Application> occasionally prints out  
messages  which
     are  often helpful during troubleshooting.  If you wish
     to view debugging messages from the <Application>postmaster</Application>, 
you can
     start  it with the -d option and redirect the output to
     the log file:
<ProgramListing>
% postmaster -d >& pm.log &
</ProgramListing>
     If you do not wish to see these messages, you can type
<ProgramListing>
% postmaster -S
</ProgramListing>
     and the <Application>postmaster</Application> will be "S"ilent.  
Notice that there
     is no ampersand ("&amp") at the end of the last example.
</Para>
</Chapter>

<Chapter Id="newuser">
<Title>Adding and Deleting Users</Title>

<Para>
     <Application>createuser</Application> enables specific users to access
     <ProductName>Postgres</ProductName>.  
<Application>destroyuser</Application> removes  users  and
     prevents them from accessing <ProductName>Postgres</ProductName>.  
Note that these
     commands only affect users with  respect  to  
<ProductName>Postgres</ProductName>;
     they  have  no  effect on users other privileges or status with regards
to the underlying 
     operating system.
</Para>
</Chapter>

<Chapter Id="disk">
<Title>Disk Management</Title>

<Para>
</Para>

<Sect1>
<Title>Alternate Locations</Title>

<Para>
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.
</para>
<Para>
 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.
</para>
<Note>
<Para>
 In previous versions of <ProductName>Postgres</ProductName>, 
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 <ProductName>Postgres</ProductName>
 To do this, either add this line
<ProgramListing>
#define ALLOW_ABSOLUTE_DBPATHS 1
</ProgramListing>
to the file <filename>src/include/config.h</filename>, or by specifying
<ProgramListing>
 CFLAGS+= -DALLOW_ABSOLUTE_DBPATHS
</ProgramListing>
in your <filename>Makefile.custom</filename>.
</Para>
</Note>

<Para>
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 <filename>/home/postgres/data</filename>, first type
<ProgramListing>
% setenv PGDATA2 /home/postgres/data
</ProgramListing>
to define the environment variable to be used with subsequent commands.
Usually, you will want to define this variable in the 
<ProductName>Postgres</ProductName> superuser's
<filename>.profile</filename>
or
<filename>.cshrc</filename>
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.
</para>
<Para>
To create a data storage area in PGDATA2, ensure
that <filename>/home/postgres</filename> already exists and is writable 
by the postgres administrator.
Then from the command line, type
<ProgramListing>
% setenv PGDATA2 /home/postgres/data
% initlocation $PGDATA2
Creating Postgres database system directory /home/postgres/data

Creating Postgres database system directory /home/postgres/data/base

</ProgramListing>
</para>
<Para>
To test the new location, create a database <Database>test</Database> by typing
<ProgramListing>
% createdb -D PGDATA2 test
% destroydb test
</ProgramListing>
</para>
</Sect1>
</Chapter>

<Chapter Id="trouble">
<Title>Troubleshooting</Title>

<Para>
     Assuming that  your  site  administrator  has  properly
     started  the  <Application>postmaster</Application>  process 
and authorized you to use the database, you (as a user) may begin to start up
     applications.   As previously mentioned, you should add
     <filename>/usr/local/pgsql/bin</filename> to your  shell  search  path.
     In  most  cases,  this  is all you should have to do in
     terms of preparation.
</para>
<Para>
     If  you get the following error message from a 
<ProductName>Postgres</ProductName>
     command (such as <Application>psql</Application> or 
<Application>createdb</Application>):
<ProgramListing>
connectDB() failed: Is the postmaster running at 'localhost' on port '5432'?
</ProgramListing>
     it is usually because either the <Application>postmaster</Application> is not running,
 or you are attempting to connect to the wrong server host.
     If you get the following error message:
<ProgramListing>
FATAL 1:Feb 17 23:19:55:process userid (2360) != database owner (268)
</ProgramListing>
     it means that the site administrator started the  <Application>postmaster</Application>
  as  the  wrong user.  Tell him to restart it as
     the <ProductName>Postgres</ProductName> superuser.
</Para>
</Chapter>

<Chapter Id="manage-ag">
<Title>Managing a Database</Title>

<Para>
     Now that <ProductName>Postgres</ProductName> is up and running we can create
  some     databases  to  experiment  with.  Here, we describe the
     basic commands for managing a database.
</Para>

<Sect1>
<Title>Creating a Database</Title>

<Para>
     Let's say you want to create  a  database  named  mydb.
     You can do this with the following command:
<ProgramListing>
% createdb mydb
</ProgramListing>

     <ProductName>Postgres</ProductName>  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 <ProductName>Postgres</ProductName> 
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.
</Para>
</Sect1>

<Sect1>
<Title>Accessing a Database</Title>

<Para>
     Once you have constructed a database, you can access it
     by:

<ItemizedList Mark="bullet" Spacing="compact">
<ListItem>
<Para>
running the <ProductName>Postgres</ProductName>  terminal  monitor  program 
(<Application>psql</Application>) which allows you to interactively
        enter, edit, and execute <Acronym>SQL</Acronym> commands.
</Para>
</ListItem>
<ListItem>
<Para>
      writing a  C  program  using  the  <literal>libpq</literal>  subroutine
        library.   This  allows  you  to submit <Acronym>SQL</Acronym> commands
        from C and get answers and status messages  back  to
        your  program.   This interface is discussed further
        in the <citetitle>PostgreSQL Programmer's Guide</citetitle>.
</Para>
</ListItem>
</ItemizedList>

     You might want to start up <Application>psql</Application>, 
to try out  the  examples  in  this manual. It can be activated for the mydb
     database by typing the command:
<ProgramListing>
% psql mydb
</ProgramListing>

     You will be greeted with the following message:
<ProgramListing>
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=>
</ProgramListing>
</Para>

<Para>
This prompt indicates that the terminal monitor is listening  
to you and that you can type <Acronym>SQL</Acronym> queries into a
     workspace maintained by the terminal monitor.
     The <Application>psql</Application> program responds to escape
  codes  that  begin
     with  the  backslash  character, "\".  For example, you
     can get help on the syntax of various 
<ProductName>Postgres</ProductName> <Acronym>SQL</Acronym> commands by typing:
<ProgramListing>
mydb=> \h
</ProgramListing>

     Once  you  have finished entering your queries into the
     workspace, you can pass the contents of  the  workspace
     to the <ProductName>Postgres</ProductName> server by typing:
<ProgramListing>
mydb=> \g
</ProgramListing>

     This  tells  the  server  to process the query.  If you
     terminate your query with a semicolon, the  backslash-g is  not
     necessary.   <Application>psql</Application> will automatically 
process semicolon terminated queries.
     To read queries from a file,  say  myFile,  instead  of
     entering them interactively, type:
<ProgramListing>
mydb=> \i fileName
</ProgramListing>

     To get out of <Application>psql</Application> and return to UNIX, type
<ProgramListing>
mydb=> \q
</ProgramListing>

     and  <Application>psql</Application>  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 <Acronym>SQL</Acronym> queries.  
Single-line comments  are  denoted  by
     <Quote>--</Quote>.   Everything  after the dashes up to the end of the
     line is ignored. Multiple-line comments, and comments within a line,
     are denoted by <Quote>/* ... */</Quote>
</Para>
</Sect1>
     
<Sect1>
<Title>Destroying a Database</Title>

<Para>
     If you are the database administrator for the  database
     mydb,  you can destroy it using the following UNIX command:
<ProgramListing>
% destroydb mydb
</ProgramListing>
     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.
</Para>
</Sect1>

</Chapter>