postmaster1ApplicationpostmasterPostgreSQL multiuser database serverpostmasterpostmaster-A 01-B nbuffers-c name=value-d debug-level-D datadir-F-h hostname-i-k directory-l-N max-connections-o extra-options-p port-S--name=value-n-sDescriptionpostmaster is the
PostgreSQL multiuser database server.
In order for a client application to access a database it connects
(over a network or locally) to a running
postmaster. The
postmaster then starts a separate server
process () to handle
the connection. The postmaster also
manages the communication among server processes.
By default the postmaster starts in the
foreground and prints log messages to the standard error stream. In
practical applications the postmaster
should be started as a background process, perhaps at boot time.
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 (data area). This is
done with the invocation option or the
PGDATA 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
communication ports (see below). A data area is created with .
Optionspostmaster accepts the following
command line arguments. For a detailed discussion of the options
consult . You can also save typing most of these
options by setting up a configuration file.
Enables run-time assertion 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.
Sets the number of shared buffers for use by the server
processes. This value defaults to 64 buffers, where each
buffer is 8 kB.
Sets a named run-time parameter. Consult for
a list and descriptions. Most of the other command line
options are in fact short forms of such a parameter
assignment.
Sets the debug level. The higher this value is set, the more
debugging output is written to the server log. Values are from
1 to 5.
Specifies the file system location of the data directory. See
discussion above.
Disables fsync calls for performance
improvement, at the risk of data corruption in event of a
system crash. This option corresponds to setting
fsync=false> in postgresql.conf>. Read the detailed
documentation before using this!
has the opposite effect
of this option.
Specifies the IP host name or address on which the
postmaster is to listen for
connections from client applications. Defaults to
listening on all configured addresses (including
localhost).
Allows clients to connect via TCP/IP (Internet domain)
connections. Without this option, only local Unix domain
socket connections are accepted. This option corresponds
to setting tcpip_socket=true> in postgresql.conf>.
has the opposite
effect of this option.
Specifies the directory of the Unix-domain socket on which the
postmaster is to listen for
connections from client applications. The default is normally
/tmp, but can be changed at build time.
Enables secure connections using SSL. The
option is also required. You must have compiled with SSL
enabled to use this option.
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 your
system will support. (Note that
is required to be at least twice
. See for a discussion of
system resource requirements for large numbers of client
connections.)
The command line-style options specified in extra-options are passed to
all server processes started by this
postmaster. See for possibilities. If the option
string contains any spaces, the entire string must be quoted.
Specifies the TCP/IP port or local Unix domain socket file
extension on which the postmaster
is to listen for connections from client applications.
Defaults to the value of the PGPORT environment
variable, or if PGPORT 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 PGPORT.
Specifies that the postmaster
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 /dev/null.
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.
has the opposite effect
of this option.
Sets a named run-time parameter; a shorter form of
Two additional command line options are available for debugging
problems that cause a server process to die abnormally. The
ordinary strategy in this situation is to notify all other server
processes that they must terminate and then reinitialize the
shared memory and semaphores. This is because an errant server
process could have corrupted some shared state before terminating.
These options select alternative behaviors of the
postmaster in this situation.
Neither option is intended for use in ordinary
operation.
These special-case options are:
postmaster
will not reinitialize shared data structures. A knowledgeable system
programmer can then use a debugger
to examine shared memory and semaphore state.
postmaster
will stop all other server processes by sending the signal
SIGSTOP,
but will not cause them to terminate. This permits system programmers
to collect core dumps from all server processes by hand.
EnvironmentPGCLIENTENCODING
Default character encoding used by clients. (The clients may
override this individually.) This value can also be set in the
configuration file.
PGDATA
Default data direction location
PGDATESTYLE
Default value of the DATESTYLE run-time
parameter. (The use of this environment variable is deprecated.)
PGPORT
Default port (preferably set in the configuration file)
TZ
Server time zone
others
Other environment variables may be used to designate alternative
data storage locations. See for more
information.
Diagnostics
A failure message mentioning semget> or shmget>
probably indicates you need to configure your kernel to provide adequate
shared memory and semaphores. For more discussion see .
You may be able to postpone reconfiguring your kernel by decreasing
shared_buffers to reduce the shared memory consumption
of PostgreSQL>, and/or by reducing
max_connections to reduce the semaphore consumption.
A failure message suggesting that another postmaster is already running
should be checked carefully, for example by using the command
$ps ax | grep postmaster
or
$ps -ef | grep postmaster
depending on your system. If you are certain that no conflicting
postmaster is running, you may remove the lock file mentioned in the
message and try again.
A failure message indicating inability to bind to a port may
indicate that that port is already in use by some
non-PostgreSQL process. You may also
get this error if you terminate the postmaster
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 trusted and only permit
the Unix superuser to access them.
Notes
If at all possible, do not use
SIGKILL to kill the
postmaster. Doing so will prevent
postmaster from freeing the system
resources (e.g., shared memory and semaphores) that it holds before
terminating. This may cause problems for starting a fresh
postmaster run.
To terminate the postmaster normally,
the signals SIGTERM, SIGINT,
or SIGQUIT 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 proper shutdown, resulting in a recovery run
during restart. The SIGHUP signal will
reload the server configuration files.
The utility command can be used to
start and shut down the postmaster
safely and comfortably.
The Examples
To start postmaster in the background
using default values, type:
$nohup postmaster >logfile 2>&1 </dev/null &
To start postmaster with a specific
port:
$postmaster -p 1234
This command will start up postmaster
communicating through the port 1234. In order to connect to this
postmaster using psql>, you would need to
run it as
$psql -p 1234
or set the environment variable PGPORT:
$export PGPORT=1234$psql
Named run-time parameters can be set in either of these styles:
$postmaster -c sort_mem=1234$postmaster --sort-mem=1234
Either form overrides whatever setting might exist for SORT_MEM>
in postgresql.conf>. Notice that underscores in parameter
names can be written as either underscore or dash on the command line.
Except for short-term experiments,
it's probably better practice to edit the setting in
postgresql.conf> than to rely on a command-line switch
to set a parameter.
See Also,