POSTMASTER(1) PostgreSQL Server Applications POSTMASTER(1)NAMEpostmaster - PostgreSQL multi-user database server
SYNOPSISpostmaster [ -A { 0 | 1 } ] [ -B nbuffers ] [ -c name=value ] [ -d
debug-level ] [ -D datadir ] [ -F ] [ -h hostname ] [ -i ] [ -k direc‐
tory ] [ -l ] [ -N max-connections ] [ -o extra-options ] [ -p port ] [
-S ] [ -n | -s ]
DESCRIPTIONpostmaster is the PostgreSQL multi-user 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 sepa‐
rate server process (``postgres(1)'') to handle the connection. The
postmaster also manages the communication among server processes.
By default the postmaster starts in the foreground and prints log mes‐
sages 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 clus‐
ter. 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 vari‐
able; 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 dif‐
ferent communication ports (see below). A data area is created with
initdb(1).
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 pro‐
cesses. 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 assign‐
ment.
On some systems it is also possible to equivalently use GNU-
style long options in the form --name=value.
-d debug-level
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.
-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. Read the detailed documentation before using
this!
-h hostname
Specifies the TCP/IP hostname 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) connec‐
tions. Without this option, only local Unix domain socket con‐
nections are accepted.
-k directory
Specifies the directory of the Unix-domain socket on which the
postmaster is to listen for connections from client applica‐
tions. 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 postmas‐
ter 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 -B is required to be at least twice -N.)
-o extra-options
The command line-style options specified in extra-options are
passed to all backend server processes started by this postmas‐
ter. See postgres(1) 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 (control‐
ling) 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 trou‐
bleshoot problems. See below for a better way to start the post‐
master in the background.
Two additional command line options are available for debugging prob‐
lems 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 back‐
ends 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:
-npostmaster will not reinitialize shared data structures. A
knowledgeable system programmer can then use a debugger to exam‐
ine shared memory and semaphore state.
-spostmaster will stop all other backend processes by sending the
signal SIGSTOP, but will not cause them to terminate. This per‐
mits system programmers to collect core dumps from all backend
processes by hand.
OUTPUTS
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 Postgres' shared memory consumption,
and/or by reducing -N to reduce Postgres' 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 com‐
mand
$ 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 termi‐
nate 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 lengthy shutdown, resulting in
a recovery run during restart.
The utility command pg_ctl(1) can be used to start and shut down the
postmaster safely and comfortably.
USAGE
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
Application 2000-12-25 POSTMASTER(1)
