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Support Docs & Contrib
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Marc G. Fournier
323
doc/man/postmaster.1
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323
doc/man/postmaster.1
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.\" This is -*-nroff-*-
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.\" XXX standard disclaimer belongs here....
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.\" $Header: /cvsroot/pgsql/doc/man/Attic/postmaster.1,v 1.1.1.1 1996/08/18 22:14:26 scrappy Exp $
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.TH POSTMASTER UNIX 11/05/95 Postgres95 Postgres95
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.SH "NAME"
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postmaster \(em run the Postgres postmaster
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.SH "SYNOPSIS"
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.BR "postmaster"
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[\c
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.BR "-B"
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n_buffers]
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[\c
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.BR "-D"
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data_dir]
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[\c
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.BR "-S" \c
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]
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[\c
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.BR "-a"
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system]
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.br
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.in +5n
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[\c
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.BR "-b"
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backend_pathname]
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[\c
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.BR "-d"
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[debug_level]]
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[\c
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.BR "-n" \c
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]
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.br
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[\c
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.BR "-o"
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backend_options]
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[\c
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.BR "-p"
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port]
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[\c
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.BR "-s" \c
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]
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.in -5n
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.SH "DESCRIPTION"
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The
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.IR "postmaster"
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manages the communication between frontend and backend processes, as
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well as allocating the shared buffer pool and semaphores (on machines
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without a test-and-set instruction). The
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.IR postmaster
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does not itself interact with the user and should be started as a
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background process.
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.BR "Only one postmaster should be run on a machine."
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.PP
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The
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.IR "postmaster"
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understands the following command-line options:
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.TP 5n
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.BR "-B" " n_buffers"
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.IR "n_buffers"
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is the number of shared-memory buffers for the
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.IR "postmaster"
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to allocate and manage for the backend server processes that it
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starts. This value defaults to 64.
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.TP
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.BR "-D" " data_dir"
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Specifies the directory to use as the root of the tree of database
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directories. This directory uses the value of the environment
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variable
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.SM PGDATA.
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If
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.SM PGDATA
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is not set, then the directory used is
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.SM $POSTGRESHOME\c
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/data. If neither environment variable is set and this command-line
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option is not specified, the default directory that was
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set at compile-time is used.
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.TP
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.BR "-S"
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Specifies that the
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.IR "postmaster"
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process should start up in silent mode. That is, it will disassociate
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from the user's (controlling) tty and start its own process group.
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This should not be used in combination with debugging options because
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any messages printed to standard output and standard error are
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discarded.
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.TP
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.BR "-a" " system"
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Specifies whether or not to use the authentication system
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.IR "system"
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(see
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.IR introduction (1))
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for frontend applications to use in connecting to the
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.IR postmaster
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process. Specify
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.IR "system"
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to enable a system, or
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.BI "no" "system"
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to disable a system. For example, to permit users to use
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.IR Kerberos
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authentication, use
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.BR "-a kerberos" ;
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to deny any unauthenticated
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connections, use
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.BR "-a nounauth .
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The default is site-specific.
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.TP
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.BR "-b" " backend_pathname"
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.IR "backend_pathname"
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is the full pathname of the Postgres backend server executable file that
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the
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.IR "postmaster"
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will invoke when it receives a connection from a frontend application.
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If this option is not used, then the
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.IR postmaster
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tries to find this executable file in the directory in which its own
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executable is located (this is done by looking at the pathname under
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which the
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.IR "postmaster"
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was invoked. If no pathname was specified, then the
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.SM PATH
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environment variable is searched for an executable named
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\*(lqpostgres\*(rq).
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.TP
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.BR "-d" " [debug_level]"
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The optional argument
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.IR debug_level
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determines the amount of debugging output the backend servers will
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produce.
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If
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.I debug_level
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is one, the postmaster will trace all connection traffic,
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and nothing else.
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For levels two and higher,
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debugging is turned on in the backend process and the postmaster
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displays more information,
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including the backend environment and process traffic.
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Note that if no file is specified for backend servers to
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send their debugging output then this output will appear on the
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controlling tty of their parent
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.IR postmaster .
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.TP
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.BR "-n" ", " "-s"
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The
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.IR "-s" " and " "-n"
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options control the behavior of the
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.IR "postmaster"
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when a backend dies abnormally. \fBNeither option is intended for use in
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ordinary operation\fP.
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.IP
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The ordinary strategy for this situation is to notify all other
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backends that they must terminate and then reinitialize the shared
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memory and semaphores. This is because an errant backend could have
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corrupted some shared state before terminating.
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.IP
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If the
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.IR "-s"
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option is supplied, then the
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.IR "postmaster"
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will stop all other backend processes by sending the signal
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.SM SIGSTOP,
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but will not cause them to terminate. This permits system programmers
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to collect core dumps from all backend processes by hand.
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.IP
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If the
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.IR "-n"
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option is supplied, then the
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.IR "postmaster"
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does not reinitialize shared data structures. A knowledgable system
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programmer can then use the
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.IR shmemdoc
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program to examine shared memory and semaphore state.
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.TP
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.BR "-o" " backend_options"
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The
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.IR postgres (1)
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options specified in
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.IR "backend_options"
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are passed to all backend server processes started by this
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.IR postmaster .
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If the option string contains any spaces, the entire string must be
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quoted.
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.TP
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.BR "-p" " port"
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Specifies the Internet TCP port on which the
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.IR postmaster
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is to listen for connections from frontend applications. Defaults to
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5432, or the value of the
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.SM PGPORT
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environment variable (if set). If you specify a port other than the
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default port then all frontend application users must specify the same
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port (using command-line options or
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.SM PGPORT\c
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) when starting any libpq application, including psql.
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.SH "WARNINGS"
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If at all possible,
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.BR "do not"
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use
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.SM SIGKILL
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when killing the
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.IR "postmaster" "."
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.SM SIGHUP,
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.SM SIGINT,
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or
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.SM SIGTERM
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(the default signal for
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.IR "kill" "(1))"
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should be used instead. Hence, avoid
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.nf
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kill -KILL
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.fi
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or its alternative form
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.nf
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kill -9
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.fi
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as this will prevent the
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.IR postmaster
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from freeing the system resources (e.g., shared memory and semaphores)
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that it holds before dying. This prevents you from having to deal with
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the problem with
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.IR shmat (2)
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described below.
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.SH "EXAMPLES"
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.nf
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# start postmaster using default values
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postmaster -S
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.fi
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This command will start up
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.IR "postmaster"
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on the default port (5432) and will search
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.SM $PATH
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to find an executable file called \*(lqpostgres\*(rq. This is the
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simplest and most common way to start the
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.IR "postmaster" .
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.nf
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# start with specific port and executable name
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postmaster -p -b /usr/postgres/bin/postgres &
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.fi
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This command will start up a
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.IR "postmaster"
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communicating through the port 1234, and will attempt to use the
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backend located at \*(lq/usr/postgres/bin/postgres\*(rq. In order to
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connect to this
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.IR "postmaster"
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using psql, you would need to either
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specify
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.BR "-p 1234"
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on the
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.IR "psql"
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command-line or set the environment variable
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.SM PGPORT
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to 1234.
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.SH "SEE ALSO"
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ipcs(1),
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ipcrm(1),
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ipcclean(1),
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psql(1),
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postgres(1),
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.SH "DIAGNOSTICS"
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.TP
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.BR "FindBackend: could not find a backend to execute..."
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If you see this message, you do not have the
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.IR "postgres"
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executable in your path. Add the directoy in which postgres resides to
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your path.
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.TP
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.BR "semget: No space left on device"
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If you see this message, you should run the
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.IR "ipcclean"
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command. After doing this, try starting the
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.IR "postmaster"
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again. If this still doesn't work, you probably need to configure
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your kernel for shared memory and semaphores as described in the
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installation notes. If you run multiple
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.IR postmaster s
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on a single host, or have reduced the shared memory and semaphore
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parameters from the defaults in the generic kernel, you may have to
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go back and increase the shared memory and semaphores configured
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into your kernel.
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.TP
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.BR "StreamServerPort: cannot bind to port"
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If you see this message, you should be certain that there is no other
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.IR "postmaster"
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process already running. The easiest way to determine this is by
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using the command
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.nf
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ps -ax | grep postmaster
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.fi
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on BSD-based systems
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.nf
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ps -e | grep postmast
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.fi
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(the equivalent syntax is on System V-like or POSIX-compliant systems such as HP-UX). If you
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are sure that no other
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.IR "postmaster"
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processes are running and you still get this error, try specifying a
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different port using the
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.BR "-p"
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option. You may also get this error if you terminate the
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.IR "postmaster"
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and immediately restart it using the same port; in this case, you must
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simply wait a few seconds until the operating system closes the port
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before trying again. Finally, you may get this error if you specify
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a port number that your operating system considers to be reserved.
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For example, many versions of Unix consider port numbers under 1024 to
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be \*(lqtrusted\*(rq and only permit the Unix superuser to access them.
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.TP
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.BR "IpcMemoryAttach: shmat() failed: Permission denied"
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A likely explanation is that another user attempted to start a
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.IR "postmaster"
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process on the same port which acquired shared resources and then
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died. Since Postgres shared memory keys are based on the port number
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assigned to the
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.IR "postmaster" ,
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such conflicts are likely if there is more than one installation on
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a single host. If there are no other
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.IR "postmaster"
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processes currently running (see above), run
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.IR "ipcclean"
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and try again. If other
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.IR "postmaster" s
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are running, you will have to find the owners of those processes to
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coordinate the assignment of port numbers and/or removal of unused
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shared memory segments.
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