<!-- $Header: /cvsroot/pgsql/doc/src/sgml/ref/postmaster.sgml,v 1.16 2000/11/22 01:41:13 momjian Exp $ Postgres documentation --> <refentry id="APP-POSTMASTER"> <docinfo> <date>2000-11-12</date> </docinfo> <refmeta> <refentrytitle id="APP-POSTMASTER-TITLE"><application>postmaster</application></refentrytitle> <manvolnum>1</manvolnum> <refmiscinfo>Application</refmiscinfo> </refmeta> <refnamediv> <refname id="postmaster-ref">postmaster</refname> <refpurpose><productname>PostgreSQL</productname> multi-user database server</refpurpose> </refnamediv> <refsynopsisdiv> <cmdsynopsis> <command>postmaster</command> <arg>-A <group choice="plain"><arg>0</arg><arg>1</arg></group></arg> <arg>-B <replaceable>nbuffers</replaceable></arg> <arg>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></arg> <arg>-d <replaceable>debug-level</replaceable></arg> <arg>-D <replaceable>datadir</replaceable></arg> <arg>-F</arg> <arg>-h <replaceable>hostname</replaceable></arg> <arg>-i</arg> <arg>-k <replaceable>filename</replaceable></arg> <arg>-l</arg> <arg>-N <replaceable>max-connections</replaceable></arg> <arg>-o <replaceable>extra-options</replaceable></arg> <arg>-p <replaceable>port</replaceable></arg> <arg>-S</arg> <group><arg>-n</arg><arg>-s</arg></group> </cmdsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para> <application>postmaster</application> is the <productname>PostgreSQL</productname> multi-user database server. In order for a client application to access a database it connects (over a network or locally) to a running <application>postmaster</application>. The <application>postmaster</application> then starts a separate server process (<quote><xref linkend="app-postgres" endterm="app-postgres-title"></quote>) to handle the connection. The postmaster also manages the communication among server processes. </para> <para> By default the postmaster starts in the foreground and prints log messages to the standard output. In practical applications the postmaster should be started as a background process, perhaps at boot time. </para> <para> One postmaster always manages the data from exactly one database cluster. A database cluster is a collection of databases that is stored at a common file system location. When the postmaster starts it needs to know the location of the database cluster files (<quote>data area</quote>). This is done with the <option>-D</option> invocation option or the <envar>PGDATA</envar> environment variable, there is no default. More than one postmaster process can run on a system at one time, as long as they use different data areas and different port numbers (see below). A data area is created with <xref linkend="app-initdb" endterm="app-initdb-title">. </para> <refsect2 id="app-postmaster-options"> <title>Options</title> <para> <application>postmaster</application> accepts the following command line arguments. For a detailed discussion of the options consult the <citetitle>Administrator's Guide</citetitle>. You can also save typing most of these options by setting up a configuration file. <variablelist> <varlistentry> <term>-A 0|1</term> <listitem> <para> Enables run-time assert checks, which is a debugging aid to detect programming mistakes. This is only available if it was enabled during compilation. If so, the default is on. </para> </listitem> </varlistentry> <varlistentry> <term>-B <replaceable class="parameter">nbuffers</replaceable></term> <listitem> <para> Sets the number of shared buffers for use by the server processes. This value defaults to 64 buffers, where each buffer is 8 kB. </para> </listitem> </varlistentry> <varlistentry> <term>-c <replaceable>name</replaceable>=<replaceable>value</replaceable></term> <listitem> <para> Sets a named run-time parameter. Consult the <citetitle>Administrator's Guide</citetitle> for a list and descriptions. Most of the other command line options are in fact short forms of such a parameter assignment. </para> <para> On some systems it is also possible to equivalently use GNU-style long options in the form <literal>--name=value</literal>. </para> </listitem> </varlistentry> <varlistentry> <term>-d <replaceable>debug-level</replaceable></term> <listitem> <para> Sets the debug level. The higher this value is set, the more debugging output is written to the server log. The default is 0, which means no debugging. Values up to 4 make sense. </para> </listitem> </varlistentry> <varlistentry> <term>-D <replaceable class="parameter">datadir</replaceable></term> <listitem> <para> Specifies the file system location of the data directory. See discussion above. </para> </listitem> </varlistentry> <varlistentry> <term>-F</term> <listitem> <para> Disables <function>fsync</function> calls for performance improvement at the risk of data corruption. Read the detailed documentation before using this! </para> </listitem> </varlistentry> <varlistentry> <term>-h <replaceable class="parameter">hostname</replaceable></term> <listitem> <para> Specifies the TCP/IP hostname or address on which the <application>postmaster</application> is to listen for connections from client applications. Defaults to the value of the <envar>PGHOST</envar> environment variable, or if <envar>PGHOST</envar> is not set, it defaults to listening on all configured addresses (including localhost). </para> </listitem> </varlistentry> <varlistentry> <term>-i</term> <listitem> <para> Allows clients to connect via TCP/IP (Internet domain) connections. Without this option, only local Unix domain socket connections are accepted. </para> </listitem> </varlistentry> <varlistentry> <term>-k <replaceable class="parameter">filename</replaceable></term> <listitem> <para> Specifies the directory for Unix domain socket on which the <application>postmaster</application> is to listen for connections from client applications. Defaults to the value of the <envar>PGUNIXSOCKET</envar> environment variable, or if <envar>PGUNIXSOCKET</envar> is not set, then defaults to a file in <filename>/tmp</filename>. </para> </listitem> </varlistentry> <varlistentry> <term>-l</term> <listitem> <para> Enables secure connections using SSL. The <option>-i</option> option is also required. You must have compiled with SSL enabled to use this option. </para> </listitem> </varlistentry> <varlistentry> <term>-N <replaceable class="parameter">max-connections</replaceable></term> <listitem> <para> Sets the maximum number of client connections that this postmaster will accept. By default, this value is 32, but it can be set as high as 1024 if your system will support that many processes. (Note that <option>-B</option> is required to be at least twice <option>-N</option>.) </para> </listitem> </varlistentry> <varlistentry> <term>-o <replaceable class="parameter">extra-options</replaceable></term> <listitem> <para> The command line-style options specified in <replaceable class="parameter">EXTRA-OPTIONS</replaceable> are passed to all backend server processes started by this <application>postmaster</application>. See <xref linkend="app-postgres" endterm="app-postgres-title"> for possibilities. 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 client 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 during compilation (normally 5432). If you specify a port other than the default port, then all client applications must specify the same port using either command-line options or <envar>PGPORT</envar>. </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) terminal, start its own process group, and redirect its standard output and standard error to <filename>/dev/null</filename>. </para> <para> Using this switch discards all logging output, which is probably not what you want, since it makes it very difficult to troubleshoot problems. See below for a better way to start the postmaster in the background. </para> </listitem> </varlistentry> </variablelist> </para> <para> Two additional command line options are available for debugging problems that cause a backend to die 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> <application>postmaster</application> will not reinitialize shared data structures. A knowledgeable system programmer can then use a debugger 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-2"> <title> Outputs </title> <para> <variablelist> <varlistentry> <term><computeroutput> semget: No space left on device </computeroutput></term> <listitem> <para> If you see this message, you should run the <application>ipcclean</application> command. After doing so, 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, and/or by reducing -N to reduce Postgres' semaphore consumption. </para> </tip> </para> </listitem> </varlistentry> <varlistentry> <term><computeroutput> StreamServerPort: cannot bind to port </computeroutput></term> <listitem> <para> If you see this message, you should make certain that there is no other <application>postmaster</application> process already running on the same port number. 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><computeroutput> IpcMemoryAttach: shmat() failed: Permission denied </computeroutput></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> </refsect1> <refsect1> <title>Notes</title> <para> If at all possible, <emphasis>do not</emphasis> use <literal>SIGKILL</literal> to kill the <application>postmaster</application>. This will prevent <application>postmaster</application> from freeing the system resources (e.g., shared memory and semaphores) that it holds before terminating. </para> <para> To terminate the postmaster normally, the signals <literal>SIGTERM</literal>, <literal>SIGINT</literal>, or <literal>SIGQUIT</literal> can be used. The first will wait for all clients to terminate before quitting, the second will forcefully disconnect all clients, and the third will quit immediately without lengthy shutdown, resulting in a recovery run during restart. </para> <para> The utility command <xref linkend="app-pg-ctl"> can be used to start and shut down the postmaster safely and comfortably. </para> </refsect1> <refsect1 id="app-postmaster-usage"> <title>Usage</title> <para> To start <application>postmaster</application> in the background using default values, type: <screen> <prompt>$</prompt> <userinput>nohup postmaster >logfile 2>&1 </dev/null &</userinput> </screen> </para> <para> To start <application>postmaster</application> with a specific port: <screen> <prompt>$</prompt> <userinput>postmaster -p 1234</userinput> </screen> 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 <screen> <prompt>$</prompt> <userinput>psql -p 1234</userinput> </screen> or set the environment variable <envar>PGPORT</envar>: <screen> <prompt>$</prompt> <userinput>export PGPORT=1234</userinput> <prompt>$</prompt> <userinput>psql</userinput> </screen> </para> </refsect1> </refentry> <!-- Keep this comment at the end of the file Local variables: mode: sgml sgml-omittag:nil sgml-shorttag:t sgml-minimize-attributes:nil sgml-always-quote-attributes:t sgml-indent-step:1 sgml-indent-data:t sgml-parent-document:nil sgml-default-dtd-file:"../reference.ced" sgml-exposed-tags:nil sgml-local-catalogs:"/usr/lib/sgml/catalog" sgml-local-ecat-files:nil End: -->