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PostgreSQL documentation

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<command>postgres</command> is the

<productname>PostgreSQL</productname> database server. In order

for a client application to access a database it connects (over a

network or locally) to a running <command>postgres</command>process.

network or locally) to a running <command>postgres</command>instance.

The <command>postgres</command> instance then starts a separate server

process to handle the connection.

</para>

<para>

One <command>postgres</command> instance always manages the datafrom

One <command>postgres</command> instance always manages the dataof

exactly one database cluster. A database cluster is a collection

of databases that is stored at a common file system location (the

<quote>data area</quote>). More than one

<command>postgres</command>process can run on a system at one

<command>postgres</command>instance can run on a system at one

time, so long as they use different data areas and different

communication ports (see below). When

<command>postgres</command> starts it needs to know the location

<para>

Sets the number of shared buffers for use by the server

processes. The default value of this parameter is chosen

automatically by <application>initdb</application>; refer to <xref

linkend="runtime-config-resource-memory"> for more information.

automatically by <application>initdb</application>.

Specifying this option is equivalent to setting the

<xref linkend="guc-shared-buffers"> configuration parameter.

</para>

</listitem>

</varlistentry>

<listitem>

<para>

Sets the maximum number of client connections that this

server will accept. By

default, this value is 32, but it can be set as high as your

system will support. (Note that

<option>-B</option> is required to be at least twice

<option>-N</option>. See <xref linkend="kernel-resources"> for a discussion of

system resource requirements for large numbers of client

connections.) Specifying this option is equivalent to setting the

server will accept. The default value of this parameter is chosen

automatically by <application>initdb</application>.

Specifying this option is equivalent to setting the

<xref linkend="guc-max-connections"> configuration parameter.

</para>

</listitem>

<term><option>-o <replaceable class="parameter">extra-options</replaceable></option></term>

<listitem>

<para>

The commandline-style options specified in <replaceable

The command-line-style options specified in <replaceable

class="parameter">extra-options</replaceable> are passed to

all server processes started by this

<command>postgres</command> process. If the option string contains

<title>Semi-internal Options</title>

<para>

There are several otheroptionsthat can be specified, used

mainly for debugging purposes and in some cases to assist with

Theoptionsdescribed here are used

mainly for debugging purposes, and in some cases to assist with

recovery of severely damaged databases. There should be no reason

to use them in a production database setup.These are listed

here only fortheuse by <productname>PostgreSQL</productname>

to use them in a production database setup.They are listed

here only for use by <productname>PostgreSQL</productname>

system developers. Furthermore, these options might

change or be removed in a future release without notice.

</para>

<term><replaceable class="parameter">database</replaceable></term>

<listitem>

<para>

Specifies the name of the database to be accessed. If it is

omitted it defaults to the user name.

Specifies the name of the database to be accessed. This must be

the last argument on the command line. If it is

omitted it defaults to the user name.

</para>

</listitem>

</varlistentry>

<refsect1>

<title>Notes</title>

<para>

The utility command <xref linkend="app-pg-ctl"> can be used to

start and shut down the <command>postgres</command> server

safely and comfortably.

</para>

<para>

If at all possible, <emphasis>do not</emphasis> use

all clients to terminate before quitting, the second will

forcefully disconnect all clients, and the third will quit

immediately without proper shutdown, resulting in a recovery run

during restart. The <literal>SIGHUP</literal> signal will reload

the server configuration files. It is also possible to send

<literal>SIGHUP</literal> to an individual server process, but that

is usually not sensible.

during restart.

</para>

<para>

The utility command <xref linkend="app-pg-ctl"> can be used to

start and shut down the <command>postgres</command> server

safely and comfortably.

The <literal>SIGHUP</literal> signal will reload

the server configuration files. It is also possible to send

<literal>SIGHUP</literal> to an individual server process, but that

is usually not sensible.

</para>

<para>