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postmaster accepts the following command line arguments:
-B nBuffers
Sets the number of shared-memory disk buffers for the
postmaster
to allocate for use by the backend server processes that it
starts. This value defaults to 64 buffers, where each buffer is 8k bytes
(or whatever BLCKSZ is set to in src/include/config.h).
-D DataDir
Specifies the directory to use as the root of the tree of database
directories. If -D is not given, the default data directory name is
the value of the environment variable
PGDATA.
If PGDATA is not set, then the directory used is
$POSTGRESHOME/data.
If neither environment variable is set and this command-line
option is not specified, the default directory that was
set at compile-time is used.
-N maxBackends
Sets the maximum number of backend server processes that this postmaster
is allowed to start. 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, so you'll need to
increase -B if you increase -N.)
Both the default and upper limit values for -N can be altered
when building Postgres
(see src/include/config.h).
-S
Specifies that the postmaster
process should start up in silent mode. That is, it will disassociate
from the user's (controlling) tty, start its own process group, and
redirect its standard output and standard error to
/dev/null.
Note that using this switch makes it very
difficult to troubleshoot problems, since all tracing and logging
output that would normally be generated by this postmaster and its
child backends will be discarded.
-d DebugLevel
Determines the amount of debugging output the backend servers will
produce.
If DebugLevel
is one, the postmaster will trace all connection traffic.
Levels two and higher turn on increasing amounts of debug output
from the backend processes, and the postmaster
displays more information
including the backend environment and process traffic.
Note that unless the postmaster's standard output and standard error
are redirected into a log file, all this output will appear on the
controlling tty of the postmaster.
-i
Allows clients to connect via TCP/IP (Internet domain) connections.
Without this option, only local Unix domain socket connections are
accepted.
-l
Enables secure connections using SSL. The -i option
is also required.
You must have compiled with SSL enabled to use this option.
-o BackendOptions
The
postgres
option(s) specified in
BackendOptions
are passed to all backend server processes started by this
postmaster.
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 frontend applications. Defaults to
the value of the
PGPORT
environment variable, or if PGPORT
is not set, then defaults to the value established when Postgres was
compiled (normally 5432). If you specify a port other than the
default port then all frontend applications (including
psql) must specify the same
port using either command-line options or
PGPORT.
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.
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 command
% ps -ax | grep postmaster
on BSD-based systems, or
% ps -e | grep postmast
for System V-like or POSIX-compliant systems such as HP-UX.
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.
A likely explanation is that another user attempted to start a
postmaster
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
postmaster,
such conflicts are likely if there is more than one installation on
a single host. If there are no other
postmaster
processes currently running (see above), run
ipcclean
and try again. If other postmaster
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.
Description
postmaster
manages the communication between frontend and backend processes, as
well as allocating the shared buffer pool and SysV semaphores
(on machines without a test-and-set instruction).
postmaster
does not itself interact with the user and should be started as a
background process.
Only one postmaster should be running at a time in a given
Postgres installation.
Here, an installation means a database directory and
postmaster port number.
You can run more than one postmaster on a machine only if each one has a
separate directory and port number.
Notes
If at all possible,
do not
use SIGKILL
when killing the postmaster.
SIGHUP,
SIGINT,
or
SIGTERM
(the default signal for
kill(1))"
should be used instead. Using
% kill -KILL
or its alternative form
% kill -9
will prevent postmaster
from freeing the system resources (e.g., shared memory and semaphores)
that it holds before dying. Use SIGTERM instead
to avoid having to clean up manually (as described earlier).
Useful utilities for dealing with shared memory problems include
ipcs(1),
ipcrm(1), and
ipcclean(1).
Usage
To start postmaster using default
values, type:
% nohup postmaster >logfile 2>&1 &
This command will start up postmaster
on the default port (5432). This is the
simplest and most common way to start the
postmaster.
To start postmaster with a specific port:
% nohup 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
