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First copy from the man pages.

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<refentry id="APP-POSTMASTER">
<refmeta>
<refentrytitle>
<application>postmaster</application>
</refentrytitle>
<refmiscinfo>Application</refmiscinfo>
</refmeta>
<refnamediv>
<refname id="postmaster">
<application>postmaster</application>
</refname>
<refpurpose>
Run the <productname>Postgres</productname> multi-user backend
</refpurpose>
</refnamediv>
<refsynopsisdiv>
<refsynopsisdivinfo>
<date>1999-05-19</date>
</refsynopsisdivinfo>
<synopsis>
postmaster [ -B <replaceable class="parameter">nBuffers</replaceable> ]
[ -D <replaceable class="parameter">DataDir</replaceable> ] [-N <replaceable class="parameter">nBackends</replaceable> ] [ -S ]
[ -d [ <replaceable class="parameter">DebugLevel</replaceable> ] ]
[ -i ] [ -o <replaceable class="parameter">BackendOptions</replaceable> ] [ -p <replaceable class="parameter">port</replaceable> ]
postmaster [ -n | -s ] ...
</synopsis>
<refsect2 id="R2-APP-POSTMASTER-1">
<refsect2info>
<date>1999-05-19</date>
</refsect2info>
<title>
Inputs
</title>
<para>
<application>postmaster</application> accepts the following command line arguments:
<variablelist>
<varlistentry>
<term>
-B <replaceable class="parameter">nBuffers</replaceable>
</term>
<listitem>
<para>
The number of shared-memory buffers for the
<application>postmaster</application>
to allocate and manage for the backend server processes that it
starts. This value defaults to 64 buffers, where each buffer is 8k bytes
(or whatever BLCKSZ is set to in config.h).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-D <replaceable class="parameter">DataDir</replaceable>
</term>
<listitem>
<para>
Specifies the directory to use as the root of the tree of database
directories. If -D is not given, the default data directory name is
the value of the environment variable
<envar>PGDATA</envar>.
If <envar>PGDATA</envar> is not set, then the directory used is
<filename>$POSTGRESHOME/data</filename>.
If neither environment variable is set and this command-line
option is not specified, the default directory that was
set at compile-time is used.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-N <replaceable class="parameter">nBackends</replaceable>
</term>
<listitem>
<para>
The maximum number of backend server processes that this postmaster
is allowed to start. In the default configuration, this value
is usually set
to 32, and can be set as high as 1024 if your system will support that
many processes. Both the default and upper limit values can be altered
when building <productname>Postgres</productname> (see src/include/config.h).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-S
</term>
<listitem>
<para>
Specifies that the <application>postmaster</application>
process should start up in silent mode. That is, it will disassociate
from the user's (controlling) tty and start its own process group.
This should not be used in combination with debugging options because
any messages printed to standard output and standard error are
discarded.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-d [ <replaceable class="parameter">DebugLevel</replaceable> ]
</term>
<listitem>
<para>
The optional argument <replaceable class="parameter">DebugLevel</replaceable>
determines the amount of debugging output the backend servers will
produce.
If <replaceable class="parameter">DebugLevel</replaceable>
is one, the postmaster will trace all connection traffic,
and nothing else.
For levels two and higher,
debugging is turned on in the backend process and the postmaster
displays more information,
including the backend environment and process traffic.
Note that if no file is specified for backend servers to
send their debugging output then this output will appear on the
controlling tty of their parent <application>postmaster</application>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-i
</term>
<listitem>
<para>
This enables TCP/IP or Internet domain socket communication.
Without this option, only local Unix domain socket communication is
possible.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-o <replaceable class="parameter">BackendOptions</replaceable>
</term>
<listitem>
<para>
The
<literal>postgres</literal>
options specified in
<replaceable class="parameter">BackendOptions</replaceable>
are passed to all backend server processes started by this
<application>postmaster</application>.
If the option string contains any spaces, the entire string must be
quoted.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-p <replaceable class="parameter">port</replaceable>
</term>
<listitem>
<para>
Specifies the TCP/IP port or local Unix domain socket file extension
on which the <application>postmaster</application>
is to listen for connections from frontend applications. Defaults to
the value of the
<envar>PGPORT</envar>
environment variable, or if <envar>PGPORT</envar>
is not set, then defaults to the value established when Postgres was
compiled (normally 5432). If you specify a port other than the
default port then all frontend applications (including
<application>psql</application>) must specify the same
port using either command-line options or
<envar>PGPORT</envar>.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
<para>
A few command line options are available for debugging in the case
when a backend dies abnormally.
These options control the behavior of the
<application>postmaster</application> in this situation, and
<emphasis>neither option is intended for use in
ordinary operation</emphasis>.
</para>
<para>
The ordinary strategy for this situation is to notify all other
backends that they must terminate and then reinitialize the shared
memory and semaphores. This is because an errant backend could have
corrupted some shared state before terminating.
</para>
<para>
These special-case options are:
<variablelist>
<varlistentry>
<term>
-n
</term>
<listitem>
<para>
If the <literal>-n</literal>
option is supplied, then the
<application>postmaster</application>
does not reinitialize shared data structures. A knowledgable system
programmer can then use the
<application>shmemdoc</application>
program to examine shared memory and semaphore state.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
-s
</term>
<listitem>
<para>
<application>postmaster</application>
will stop all other backend processes by sending the signal
<literal>SIGSTOP</literal>,
but will not cause them to terminate. This permits system programmers
to collect core dumps from all backend processes by hand.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
<refsect2 id="R2-APP-POSTMASTER-1">
<refsect2info>
<date>1999-05-19</date>
</refsect2info>
<title>
Outputs
</title>
<para>
<variablelist>
<!--
<varlistentry>
<term>
FindBackend: could not find a backend to execute...
</term>
<listitem>
<para>
If you see this message, you do not have the
<application>postgres</application>
executable in your path. Add the directory in which
<application>postgres</application> resides to
your path.
</para>
</listitem>
</varlistentry>
-->
<varlistentry>
<term>
semget: No space left on device
</term>
<listitem>
<para>
If you see this message, you should run the
<application>ipcclean</application>
command. After doing this, try starting
<application>postmaster</application>
again. If this still doesn't work, you probably need to configure
your kernel for shared memory and semaphores as described in the
installation notes. If you run multiple instances of
<application>postmaster</application>
on a single host, or have a kernel with particularly small shared memory
and/or semaphore limits, you may have to reconfigure your kernel to increase
its shared memory or semaphore parameters.
<tip>
<para>
You may be able to postpone
reconfiguring your kernel by decreasing -B to reduce
<productname>Postgres</productname>' shared memory
consumption, or by reducing -N to reduce Postgres' semaphore
consumption.
</para>
</tip>
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
StreamServerPort: cannot bind to port
</term>
<listitem>
<para>
If you see this message, you should be certain that there is no other
<application>postmaster</application>
process already running. The easiest way to determine this is by
using the command
<programlisting>
% ps -ax | grep postmaster
</programlisting>
on BSD-based systems, or
<programlisting>
% ps -e | grep postmast
</programlisting>
for System V-like or POSIX-compliant systems such as HP-UX.
</para>
<para>
If you
are sure that no other
<application>postmaster</application>
processes are running and you still get this error, try specifying a
different port using the
<literal>-p</literal>
option. You may also get this error if you terminate the
<application>postmaster</application>
and immediately restart it using the same port; in this case, you must
simply wait a few seconds until the operating system closes the port
before trying again. Finally, you may get this error if you specify
a port number that your operating system considers to be reserved.
For example, many versions of Unix consider port numbers under 1024 to
be <firstterm>trusted</firstterm>
and only permit the Unix superuser to access them.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term>
IpcMemoryAttach: shmat() failed: Permission denied
</term>
<listitem>
<para>
A likely explanation is that another user attempted to start a
<application>postmaster</application>
process on the same port which acquired shared resources and then
died. Since Postgres shared memory keys are based on the port number
assigned to the
<application>postmaster</application>,
such conflicts are likely if there is more than one installation on
a single host. If there are no other
<application>postmaster</application>
processes currently running (see above), run
<application>ipcclean</application>
and try again. If other <application>postmaster</application>
images
are running, you will have to find the owners of those processes to
coordinate the assignment of port numbers and/or removal of unused
shared memory segments.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsect2>
</refsynopsisdiv>
<refsect1 id="R1-APP-POSTMASTER-1">
<refsect1info>
<date>1999-05-19</date>
</refsect1info>
<title>
Description
</title>
<para>
<application>postmaster</application>
manages the communication between frontend and backend processes, as
well as allocating the shared buffer pool and SysV semaphores
(on machines without a test-and-set instruction).
<application>postmaster</application>
does not itself interact with the user and should be started as a
background process.
</para>
<para>
<emphasis>Only one postmaster should be running at a time in a given
<productname>Postgres</productname> installation.</emphasis>
Here, an installation means a database directory and
<application>postmaster</application> port number.
You can run more than one postmaster on a machine only if each one has a
separate directory and port number.
</para>
<refsect1 id="R1-APP-VACUUMDB-2">
<refsect1info>
<date>1998-10-04</date>
</refsect1info>
<title>
Notes
</title>
<para>
If at all possible,
<emphasis>do not</emphasis>
use <literal>SIGKILL</literal>
when killing the <application>postmaster</application>.
<literal>SIGHUP</literal>,
<literal>SIGINT</literal>,
or
<literal>SIGTERM</literal>
(the default signal for
<application>kill</application>(1))"
should be used instead. Using
<programlisting>
% kill -KILL
</programlisting>
or its alternative form
<programlisting>
% kill -9
</programlisting>
will prevent <application>postmaster</application>
from freeing the system resources (e.g., shared memory and semaphores)
that it holds before dying. This prevents you from having to deal with
the problem with shared memory described earlier.
</para>
<para>
Useful utilities for dealing with shared memory problems include
<application>ipcs(1)</application>,
<application>ipcrm(1</application>), and
<application>ipcclean(1)</application>.
</para>
</refsect1>
<refsect1 id="R1-APP-VACUUMDB-3">
<refsect1info>
<date>1998-10-04</date>
</refsect1info>
<title>
Usage
</title>
<para>
To start <application>postmaster</application> using default
values, type:
<programlisting>
% nohup postmaster >logfile 2>&1 &
</programlisting>
This command will start up <application>postmaster</application>
on the default port (5432). This is the
simplest and most common way to start the
<application>postmaster</application>.
</para>
<para>
To start <application>postmaster</application> with a specific port
and executable name:
<programlisting>
% nohup postmaster -p 1234 &
</programlisting>
This command will start up <application>postmaster</application>
communicating through the port 1234. In order to
connect to this <application>postmaster</application>
using psql, you would need to run it as
<programlisting>
% psql -p 1234
</programlisting>
or set the environment variable <envar>PGPORT</envar>:
<programlisting>
% setenv PGPORT 1234
% psql
</programlisting>.
</refsect1>
</refentry>
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