postmaster 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 ("postgres") 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 output. 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 -D 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 initdb.
Options
postmaster accepts the following
command line arguments. For a detailed discussion of the options
consult the Administrator's Guide. You can
also save typing most of these options by setting up a
configuration file.
-A 0|1
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.
-B nbuffers
Sets the number of shared buffers for use by the server
processes. This value defaults to 64 buffers, where each
buffer is 8 kB.
-c name=value
Sets a named run-time parameter. Consult the
Administrator's Guide for a list and
descriptions. Most of the other command line options are in
fact short forms of such a parameter assignment. -c
can appear multiple times to set multiple parameters.
-d debug-level
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.
-D datadir
Specifies the file system location of the data directory. See
discussion above.
-F
Disables fsync calls for performance
improvement, at the risk of data corruption in event of a
system crash. This parameter corresponds to setting
fsync=false in postgresql.conf. Read the detailed
documentation before using this!
--fsync=true has the opposite effect
of this option.
-h hostname
Specifies the TCP/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).
-i
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.
--tcpip_socket=false has the opposite
effect of this option.
-k directory
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.
-l
Enables secure connections using SSL. The -i
option is also required. You must have compiled with SSL
enabled to use this option.
-N max-connections
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
-B is required to be at least twice
-N. See the Administrator's
Guide for a discussion of system resource requirements
for large numbers of client connections.)
-o extra-options
The command line-style options specified in extra-options are passed to
all backend server processes started by this
postmaster. See postgres for possibilities. If the option
string contains any spaces, the entire string must be quoted.
-p port
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.
-S
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.
--silent_mode=false has the opposite effect
of this option.
--name=value
Sets a named run-time parameter; a shorter form of
-c.
Two additional command line options are available for debugging
problems that cause a backend to die abnormally. These options
control the behavior of the postmaster
in this situation, and neither option is intended for
use in ordinary operation.
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.
These special-case options are:
-n
postmaster
will not reinitialize shared data structures. A knowledgeable system
programmer can then use a debugger
to examine shared memory and semaphore state.
-s
postmaster
will stop all other backend processes by sending the signal
SIGSTOP,
but will not cause them to terminate. This permits system programmers
to collect core dumps from all backend processes by hand.
Environment
PGCLIENTENCODING
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
PGDATASTYLE
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 the Administrator's
Guide for more information.
Diagnostics
semget: No space left on device
If you see this message, you should run the
ipcclean
command. After doing so, try starting
postmaster
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
postmaster
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: You may be able to postpone
reconfiguring your kernel by decreasing -B to reduce
the shared memory consumption of PostgreSQL,
and/or by reducing -N to reduce the semaphore
consumption.
StreamServerPort: cannot bind to port
If you see this message, you should make certain that there is no
other postmaster
process already running on the same port number. The easiest way to
determine this is by using the command
$ps ax | grep postmaster
or
$ps -e | grep postmaster
depending on your system.
If you
are sure that no other
postmaster
processes are running and you still get this error, try specifying a
different port using the
-p
option. 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. This will prevent
postmaster from freeing the system
resources (e.g., shared memory and semaphores) that it holds before
terminating.
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 utility command pg_ctl can be used to
start and shut down the postmaster
safely and comfortably.
The -- options will not work on FreeBSD or OpenBSD.
Use -c instead. This is a bug in the affected operating
systems; a future release of PostgreSQL
will provide a workaround if this is not fixed.
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:
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.
Tip: 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.
