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This is a quick start guide covering the installation and configuration of PostgreSQL. This guide is complementary to the official documentation; it does not mean to supplant it.


PostgreSQL is a free and open source relational database management system (RDBMS). It supports such things as transactions, schemata and foreign keys, and is often touted to adhere to the SQL standards more strictly and be more secure, by default, than any other database, commercial or otherwise.

Visit the About page on for more information.

What this article will cover

This article will guide you through the Gentoo specific steps to install the PostgreSQL RDBMS.

The ebuild covered by this article is dev-db/postgresql.

This article assumes that you will be installing the latest, stable version of PostgreSQL; at the time of this writing, the version was 9.3.5. Adjust the commands in this article as necessary for your specific version.

About the ebuilds

The PostgreSQL ebuilds in Portage feature slotting based on the major version. This allows you to have two major versions of PostgreSQL operating simultaneously; 9.0-9.4 libraries and servers can be installed and serve at the same time. This is useful in such circumstances where you need to move data from an older database to a new database, or need to have a production and a testing database on the same machine. Also, this prevents a database, corresponding libraries or executables from being overwritten by an incompatible update. That would require migration which is described in this guide.

Additionally, bug and security fixes, which are delivered via minor version updates, can be applied without fear of corrupting the database or the PostgreSQL installation itself; 9.3.4 can be updated to 9.3.5 as they are guaranteed to be compatible and require no more interaction from you than to emerge it and restart the server process neither migration, reconfiguration nor initialization are necessary.

Read the PostgreSQL Versioning Policy for more information.

What this article will not cover

There is quite a bit that will not be covered. The official documentation is somewhere in the neighborhood of 2,000 pages. So, a lot of details will be left out in this quick start guide. Only Gentoo specific issues will be covered and some basic configuration guidelines.


USE flags

USE flags for dev-db/postgresql PostgreSQL RDBMS

debug Enable extra debug codepaths, like asserts and extra output. If you want to get meaningful backtraces see
doc Add extra documentation (API, Javadoc, etc). It is recommended to enable per package instead of globally
icu Enable ICU (Internationalization Components for Unicode) support, using dev-libs/icu
kerberos Add kerberos support
ldap Add LDAP support (Lightweight Directory Access Protocol)
llvm Add support for llvm JIT engine
lz4 Enable support for lz4 compression (as implemented in app-arch/lz4)
nls Add Native Language Support (using gettext - GNU locale utilities)
pam Add support for PAM (Pluggable Authentication Modules) - DANGEROUS to arbitrarily flip
perl Add optional support/bindings for the Perl language
python Add optional support/bindings for the Python language
readline Enable support for libreadline, a GNU line-editing library that almost everyone wants
selinux !!internal use only!! Security Enhanced Linux support, this must be set by the selinux profile or breakage will occur
server Disable to build and install the clients and libraries only.
ssl Add support for SSL/TLS connections (Secure Socket Layer / Transport Layer Security)
static-libs Build static versions of dynamic libraries as well
systemd Enable use of systemd-specific libraries and features like socket activation or session tracking
tcl Add support the Tcl language
uuid Enable server side UUID generation (via dev-libs/ossp-uuid).
xml Add support for XML files
zlib Add support for zlib compression
zstd Enable support for ZSTD compression

Information on relevant USE flags:

  • doc: Include the online documentation to be stored on your system
  • pg_legacytimestamp: Use the older, floating-point method for formatting timestamps instead of the higher resolution 64-bit integer method. Unless you had a previous installation that utilized this deprecated method, leave this USE flag disabled. Flipping 'pg_legacytimestamp' will require you to do a dump and restore if any of your databases utilize timestamps. The two methods are incompatible with each other.
  • readline: You really want this enabled. Disabling removes command line editing and history in psql.
  • selinux: This can only be enabled by using the SELinux profile.
  • uuid: Include support to generate a 128 bit random unique identifier. This is useful for merging databases together so the chances of collisions become extremely low.


root #emerge --ask dev-db/postgresql
[ebuild N ] dev-db/postgresql-9.3.5 USE="doc -kerberos -ldap -pg_legacytimestamp
  nls perl python -pg_legacytimestamp (-selinux) readline ssl -tcl -threads
  -uuid -xml zlib" LINGUAS="-af -cs -de -es -fa -fr -hr -hu -it -ko -nb -pl
  -pt_BR -ro -ru -sk -sl -sv -tr -zh_CN -zh_TW" 0 kB

You may receive a notice regarding that any of the above packages are blocked by any or all of the following packages: dev-db/postgresql-libs, dev-db/postgresql-client, or dev-db/libpq. These packages were not maintained and obsoleted (removed from the Gentoo ebuild repository). Refer to the section on migration from the previous ebuilds to the new ones to know how to handle this situation.

Preparing to initialize the database cluster

Once the packages have finished emerging, you may want to edit /etc/conf.d/postgresql-9.3. There are three lines that effect the defaults of the server and cannot be changed later without deleting the directory that contains the database cluster and reinitializing.

PGDATA defines where to place the configuration files. DATA_DIR defines where to create the database cluster and related files. PG_INITDB_OPTS may contain any extra options you would care to set. The extra options are not required as the reasonable defaults are, ahem, reasonable.

In the following example, PGDATA states that the configuration files are to be located in /etc/postgresql-9.3/ . DATA_DIR states that the database cluster should be installed to /var/lib/postgresql/9.3/data/ , which is the default. If you decide to stray from the default, bear in mind that it is a very good idea to keep the major version in the path. PG_INITDB_OPTS states that the default locale should be en_US.UTF-8 . That is, U.S. English ordering and formatting, and UTF-8 character encoding.

FILE /etc/conf.d/postgresql-9.3Example content
# Location of configuration files
# Where the data directory is located/to be created
# Additional options to pass to initdb.
# See 'man initdb' for available options.
This only determines the default locale and character encoding. You can specify different locales and/or character encodings at database creation time ( CREATE DATABASE ) in the same database cluster.

There are six locale options that can be set to override --locale= . The following table lists the six options that, if used, are to be formatted as: --option=lo_LO.ENCODING.

Option Effects
lc-collate String sort order
lc-ctype Character classification (What is a letter? Its upper-case equivalent?)
lc-messages Language of messages
lc-monetary Formatting of currency amounts
lc-numeric Formatting of numbers
lc-time Formatting of dates and times

So, if you would like the default to be English, but you want messages in, say, Swedish, then your PG_INITDB_OPTS would look like so:

PG_INITDB_OPTS="--locale=en_US.UTF-8 --lc-messages=sv_SE.UTF-8"

A complete list of language and character encodings supported by the server can be found in the documentation, but your system must also support the respective languages and character encodings. Compare the output of locale -a to the encodings in the documentation.

You can change your locale and encoding selections at database creation time. In order to change the locale for a database after you have created it, you must drop the database and start over again.

root #emerge --config dev-db/postgresql:9.3

This will create the database cluster and store all the related server files into PGDATA and DATA_DIR .


Where the configuration files are located

Sample configuration files can be found in /usr/share/postgresql-9.3 (or whatever version), see the trouble shooting section for the script.

This time the focus is upon the files in the PGDATA directory, /etc/postgresql-9.3 , instead with primary focus on the postgresql.conf and pg_hba.conf files.


This is the main configuration file. The line that you may find of immediate interest is listen_addresses . This variable defines to which addresses PostgreSQL will bind. By default, only localhost and the Unix socket are bound. Changing listen_addresses is not enough to enable remote connections. That will be covered in the next section. The official documentation is fairly easy to understand and is exhaustive on all the settings available. It would behoove you to read that in addition to what is covered here as some things may change.

Of secondary interest is the logging destination. By default, everything is logged to postmaster.log in the DATA_DIR directory. There is an entire subsection of postgresql.conf that covers a slew of options for how, what and where to log. The subsection is marked: ERROR REPORTING AND LOGGING.

Other than listen_addresses and the logging options, the rest of the defaults in postgresql.conf are reasonable enough to get you going.


The pg_hba.conf file states who is allowed to connect to the database server and which authentication method must be used to establish the connection. Again, the documentation is quite exhaustive on the settings and what they all mean, but a few things are covered here for clarification.

FILE pg_hba.confDefault settings
# "local" is for Unix domain socket connections only
local   all         all                               trust
# IPv4 local connections:
host    all         all          trust
# IPv6 local connections:
host    all         all         ::1/128               trust

As has been mentioned before, by default the server is secure. Kind of. There is only one database role that is available for log in by default: postgres . And, the only way to initiate a connection to the database is through the /run/postgresql/.s.PGSQL.5432 Unix socket, which is owned by the postgres system user and system group, or via localhost. Now for the "kind of" bit: Any user on the system can make a connection to the database through the localhost. Even as the postgres database superuser.

Never disable the Unix socket entirely. The initscripts require access to it in order to operate properly. The method can be changed freely.

The trust method is fine vor playing on a local system. If more then one user working on your system, you will probably use peer ([ | s. docu for more details). For remote connection, use scram-sha-256 and allow only hosts in your network. (The trust method is what allows any user to log on as any user without a password. It specifies just what it implies: Trust all connections for the given type to the given database from the given database user (but not the system user) from the given location without a password. This is what allows any user on the system to log on as any user through the localhost connection from the get go. This is not as dangerous as it seems, but does pose a serious security risk in most circumstances.)

The two methods you will most likely use are: peer for local connection (have a look to ident map) and scram-sha-256 (md5 is broken! The password method only specifies that a password is required to start the connection and the password is sent "in-the-clear". This method is fine when such information will never leave the machine, such as connecting via the Unix socket or localhost. The md5 method is like password, but protects the password by using an md5 hash.)

At this point, this author would like to bring your attention to the last two lines, four lines including comments, of the pg_hba.conf file. PostgreSQL has native support for IPv6 regardless of your desires for such support. Additionally, IPv4 addresses are automatically mapped to IPv6 addresses, i.e. , will be mapped to ::FFFF: and as "pure" IPv6 ::FFFF:7F00:0001.

There seems to be some misunderstanding, though, as to how host names are mapped to IP addresses. Let us take a look at the /etc/hosts file.

FILE /etc/hosts
# IPv4 and IPv6 localhost aliases       localhost
::1             localhost

From the example above you can see that both an IPv4 and an IPv6 IP address are mapped to localhost. When psql refers to this file, it will grab the first match and use that as the address; in this case When PostgreSQL parses this, it will match the IPv6 formatted address as well, e.g. ::ffff: If, however, the IPv6 address appears first, then psql will map to ::1 alone; ::1 is not the same as ::ffff: As such, if you do not have ::1 as a permitted means of access, psql will not be able to establish a connection. Furthermore, your kernel needs to support the IPv6 protocol.

So, it is better to specify IP addresses alone to psql and in pg_hba.conf rather than to rely on /etc/hosts to be ordered properly, and it removes any doubt as to which IP addresses are allowed or to which server you will connect.

Starting the server

Give it a go!

Now start PostgreSQL and set the password for the database superuser postgres.

Change 'trust' to 'password' for the 'host' (not the 'local', Unix domain socket) connections.

root #nano -w /etc/postgresql-9.3/pg_hba.conf

Now start the database:

root #/etc/init.d/postgresql-9.3 start
postgresql-9.3  | * Starting PostgreSQL ...                             [ ok ]

Open a connection to the server and set the password:

root #psql -U postgres
psql (9.3.5)
Type "help" for help.
Enter new password:
Enter it again:

Change 'trust' to 'password' for the local connection:

root #nano -w /etc/postgresql-9.3/pg_hba.conf

Now have the database reload the configuration:

root #/etc/init.d/postgresql-9.3 reload
postgresql-9.3 | * Reloading PostgreSQL configuration ...               [ ok ]

Finally, once everything works as it should, have PostgreSQL start at boot:

root ## rc-update add postgresql-9.3 default
 * service postgresql-9.3 added to runlevel default

At this point you are ready to continue on with the official PostgreSQL Tutorial. The tutorial will guide you through creating roles, databases, schemata and all that fun and useful stuff.

Migrating PostgreSQL

When you need to migrate

If you are moving from one major version to another, e.g. from PostgreSQL 12.17 to 15.5, (but not from 12.16 to 12.17) you must migrate your data.

Perform the migration

For a migration you need the old and the new binary files as well as the data files.

All steps should done as user postgres.

First do a check:

user $ pg_upgrade15 -b /usr/lib64/postgresql-12/bin/ -B /usr/lib64/postgresql-15/bin/ -d /var/lib/postgresql/12/data/ -D /var/lib/postgresql/15/data/ --check

If something looks wrong, you'll (usually) get a hint on what to do.

If it works, you get:

  *Clusters are compatible*


Now you can start:

user $ pg_upgrade15 -b /usr/lib64/postgresql-12/bin/ -B /usr/lib64/postgresql-15/bin/ -d /var/lib/postgresql/12/data/ -D /var/lib/postgresql/15/data/

There are more information about this tool in the PostgreSQL documentation. (in particular, you will want to take a look at 'copy' or 'link')

Post migration steps

There are still a few things that should be done to complete the migration. (pg_upgrade writes a corresponding note at the end and generates the necessary scripts)

Update extensions:

user $psql -f update_extensions.sql

No statistics are transferred during migration. It therefore makes sense to execute this command:

user $/usr/lib64/postgresql-15/bin/vacuumdb --all --analyze-in-stages


user $ ./


old cluster uses data checksums but the new one does no

This mean you have done the initdb or emerge config postgresql:15 not with enabled checksums.

You will have checksums enable!

You can fix it:

user $pg_checksums15 -e /var/lib/postgresql/15/data
old cluster does not use data checksums but the new one does
  1. enable checksum on the old cluster pg_checksums12 -e /var/lib/postgresql/12/data
  2. repeat the migration.


  1. remove checksum from the new cluster pg_checksums12 -d /var/lib/postgresql/12/data
  2. do the migration
  3. enable checksum on the new cluster pg_checksums15 -e /var/lib/postgresql/15/data



pgAdmin is a graphical utility for managing PostgreSQL. It is available as dev-db/pgadmin4.


PgBouncer is a connection pooling service. It is available as dev-db/pgbouncer.

Its main design goal is improving performance of short-lived connections.[1]


Obsolete ebuilds

If any of the following PostgreSQL ebuilds are installed on the system, then the system is using a very old, obsolete installation of PostgreSQL and should migrate now: dev-db/postgresql-libs, dev-db/postgresql-client, dev-db/libpq, and dev-db/postgresql older than 9.0.

The split ebuilds named dev-db/postgresql-docs, dev-db/postgresql-base, and/or dev-db/postgresql-server have been unified into a single atomic ebuild: dev-db/postgresql. Nothing is required to move from the split ebuilds to the unified ebuild other than to emerge the unified ebuild.

This article does cover migrating from the old ebuilds to the new ones.

Server lacks instrumentation functions

This problem is easy to solve, with the solution depending on the version you are using. What is difficult about it is finding the answer. What is required is an import from a file that already exists on the storage drive: adminpack.sql . To resolve this issue, run one of the following commands appropriate to the version you have.

For PostgreSQL 9.0 and earlier:

user $psql -U postgres --file /usr/share/postgresql-9.0/contrib/adminpack.sql

For PostgreSQL 9.1 and later:

user $psql -U postgres -c "CREATE EXTENSION adminpack;"

Missing config files in /etc/postgresql-9.x and /var/lib/postgresql/9.x/data

You can try to move the config files into the directory, where x is your postgresql version number, as follows:

root #cp /var/lib/postgresql/9.x/data/*.conf /etc/postgresql-9.x/

If those files are missing you will need to initialize them.

First su into the postgres user:

root #su postgres

Then, as the postgres user, run initdb and specify the data directory:

user $initdb -D /var/lib/postgresql/9.x/data/

This will generate your configuration files and allow you to copy them over to /etc/postgresql-9.x/ as shown in the first command in this section.

"ERROR: timezone directory stack overflow" or "FATAL: too many private dirs demanded"

This is caused by a symlink loop. To fix it, type the following:

root #rm /usr/share/zoneinfo/posix

Keep in mind that any update to zoneinfo will recreate this symlink, thus requiring you to remove it again.


Force the service to start on bootup:

root #systemctl enable postgresql-9.4

To start service immediately:

root #systemctl start postgresql-9.4

If an error occurs check if the /run/postgresql/ directory is there. If not, then create it like so:

root #systemd-tmpfiles --create

Check the config file permissions:

root #ls -l /etc/postgresql-9.*/*
root #chown postgres:postgres /etc/postgresql-9.*/*
root #chmod 600 /etc/postgresql-9.*/*

Service file and changes to it

Systemd service files (postgresql-@SLOT@-.service) can be found in /lib/systemd/system/:

example config change:

FILE /lib/systemd/system/postgresql-@SLOT@.serviceExample config port change

This will override the setting appearing in /lib/systemd/system/postgresql-@SLOT@.service.

(source: postgresql-10.service file)


PostgreSQL recommends in to change the RemoveIPC setting to no in /etc/systemd/logind.conf:

FILE /etc/systemd/logind.confRemoveIPC


This page is based on a document formerly found on our main website
The following people contributed to the original document: Aaron W. Swenson,Mikkel A. Clausen
They are listed here because wiki history does not allow for any external attribution. If you edit the wiki article, please do not add yourself here; your contributions are recorded on each article's associated history page.


  1. PgBouncer command-line usage, pgbouncer. Retrieved on February 11, 2022