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PostgreSQL teaching and research databases

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What PostgreSQL resources are available?

The school maintains two PostgreSQL servers, one for teaching and one for research. Staff and students can be granted access to either server as appropriate.

Generally there is no limit on research database use, but where consumption of resources becomes detrimental to other users of the server we may request that you source dedicated server hardware.

What versions are installed?

It depends!

On DICE desktops and servers we usually carry two versions of PostgreSQL: one older version as maintained by our upstream Scientific Linux distribution (9.2 on SL7) and a newer version (presently 9.6) maintained for use by servers and clients connecting to those servers. We also install other versions and will do this on request.

You can see which versions are available with something like:

 # this is an example - your versions might differ
 $ ls /usr/bin/psql*
 /usr/bin/psql  /usr/bin/psql95

 $ psql --version
 psql (PostgreSQL) 9.2.15

 $ psql95 --version
 psql (PostgreSQL) 9.5.1

The same convention is used for differing versions of other tools:

 $ ls /usr/bin/pg_dump*
 /usr/bin/pg_dump /usr/bin/pg_dumpall 
 /usr/bin/pg_dump96 /usr/bin/pg_dumpall96

note that while clients are usually compatible with servers of different versions, a warning is given:

$ psql -h pgteach
  WARNING: psql version 9.2, server version 9.6.
           Some psql features might not work.
  SSL connection (cipher: DHE-RSA-AES256-GCM-SHA384, bits: 256)
  Type "help" for help.

or in the case of tools like pg_dump, an error:

 $ pg_dump -h servername mydatabase
 pg_dump: server version: 9.4.7; pg_dump version: 9.2.15
 pg_dump: aborting because of server version mismatch

in this case you should use the matching version where possible, replacing psql, pg_dump, or whatever command with the appropriate version, e.g. psqlXX or pg_dumpXX.


How do I get a PostgreSQL account / database?

For most students and teaching users this is entirely automatic. You will receive an account if you are taking any courses which requires one. Once you drop this course, your access will be suspended and, ultimately, any stored data removed (unless you request otherwise). You can check if you have an account by following the instructions below. If you do not have an account but feel you are entitled to one, please get in touch with support noting any course or supervisor details you think are relevant.

If you are a member of staff and would like an account, you may request one using the support form. Please state whether the account is to be used for teaching or research, and if it is to be shared with anybody.

How long can I keep my account?

If you are an undergraduate student, and have been granted a postgresql database as part of a course you are taking, your account and database will be made available in time for your coursework, and removed when it ends. If you wish to retain your account for longer than this, please contact support.

How do I access my database?

From any DICE machine (except certain research group servers), simply type the following:

psql -h pgteach


psql -h pgresearch

You will be connected to your database on the database server. If you have been given access to a named database (for example a shared group database) then you may access it by specifying the name of the database at the shell:

psql -h pgresearch databasename

If you are not on a DICE machine, the only recommended connection method is to use SSH to connect to a DICE machine, and then to use psql.

I tried typing psql, but got an error

  • While attempting to connect to your database you may receive the following error:

    psql: krb5_sendauth: Ticket expired

    This is most likely because you have been logged in for a long time, or perhaps left your computer locked overnight. The solution is simply to issue the following command at a terminal:


    You will be prompted for your DICE password.

    A similar error can be found if you clear out the contents of /tmp on your machine:

    psql: pg_krb5_init: krb5_cc_get_principal: No credentials cache found

    This can be avoided by not deleting files named /tmp/krb5cc_*, and is solved by the renc procedure described above.

    If you have any other problems, feel free to contact support. Copy or write the error message into the form if possible.

  • If you're attempting to use your scripting password (see below) and receive an error relating to GSSAPI it's likely that you've not disabled SSL. See Why is my script's SSL connection breaking? below.


Can I install my own extensions?

No, but we will be able to install some extensions on your behalf. Generally we should be able to add any of the standard "contrib" extensions on a per-account basis. We might also grant permission to install some third-party extensions where we're confident that they will not be detrimental to the server. Extensions won't typically be installed for students unless needed for a course or project.

Can I use PostGIS?

Yes, PostGIS is a good example of a well-supported third-party extension. We will install this on request.

Are there any catches with third-party extensions?

The continued operation and compatibility of third-party extensions can't be guaranteed across major database upgrades (which, typically, happen annually at most). If we encounter problems with third-party extensions on a shared server we may have to arrange alternative hosting with you.


How do I use my database with scripts or other applications?

Your regular database access is authenticated using Kerberos; this means that, while using PSQL, you will not need to enter your password to access databases. For convenience however we also permit access with a password, for scripted access where it is not possible or convenient to use stored Kerberos credentials.

If you have not set a password, your account will have have none. This denies all password attempts. To create a password, follow the instructions for resetting your password below.

Why is my script's SSL connection breaking?

Sorry, but at present, SSL is only allowed for Kerberos-authenticated clients (typically, just interactive psql sessions). If you are connecting with your password, you must use a regular, unsecured connection (with a few specific exceptions).

Exceptions have been made for a number of web servers, including Groups and Homepages, so that both SSL and non-SSL connections will work.

You can force PHP not to use SSL by adding "sslmode=disable" to your list of pg_connect options, for example using PHP:

    $dbconn = pg_connect ("host=$server dbname=$db user=$username password=$password sslmode=disable")

If you are using the interactive psql client in a script, setting the $PGSSLMODE environment variable to 'disable' before running psql will have a similar effect.

The sslmode parameter and $PGSSLMODE environment variable are amongst the standard connection parameters defined in libpq, the PostgreSQL client library on which most clients are based. You'll find that this trick also works for the likes of popular python PostgreSQL module psycopg2, for example.

I'm using a shared database. Can I give access to another user?

You can do this using the SQL GRANT and REVOKE commands to give access to other users, either on an individual table basis or en masse using the "ALL IN SCHEMA" clause.

PostgreSQL provides documentation on all of the above: a good starting point might be the GRANT command.

Some examples:

-- Check who has permission to access your tables using 
-- the postgresql \z and \dp commands.

myuser=> \z
                Access privileges
 Schema |    Name     | Type  | Access privileges
 public | foo         | table |
 public | bar         | table |

-- Remember that in this example myuser has implicit access 
--  to the database: it's the owner.

myuser=> GRANT SELECT ON foo TO another;

myuser=> \z
                   Access privileges
 Schema |    Name     | Type  |    Access privileges
 public | foo         | table | another=arwd/myuser
 public | bar         | table | another=r/myuser

-- Using the schema noted above (default in postgresql is 'public')
-- it is simple to revoke privileges from all tables, if you wish:

myuser=> REVOKE ALL ON ALL TABLES IN SCHEMA public FROM another;

I am trying to empty a table but it is taking ages. Should I just keep trying until the database server breaks?

This shouldn't happen, but massive DELETE FROM ... statements can take ages due to a quirk of the combination of PostgreSQL version and file system used on DICE servers.

It will help you (and please Support) greatly if you empty very large tables in a more efficient way:

  myuser=> TRUNCATE TABLE tablename

But it would be wise to read the postgresql documentation on the TRUNCATE command and to please make sure you have a copy of any important data before deciding to TRUNCATE it.

I left my scripting password on a post-it note in a lab/at a conference. How can I change it?

Note your password is your responsibility, and should be secret. Don't write it down.

Most users can change their own passwords in postgres. (note the quotes in the commands below; they are important)

  • Log in to your account on pgteach/pgresearch from any desktop DICE machine. You will not be required to enter a password.
  • Now change your main account password to match:
    myuser=> ALTER ROLE username WITH password 'new password here';

Alternatively, if you have no Kerberos access to your account, and no password, support can reset the password on your behalf. Be sure to change it (using the above) as soon as you have received the new password.

I've forgotten my password, and lost the post-it note. How can I reset it?

Your password is not stored in accessible form anywhere, but you don't need to know your password to change it. Simply reset it as above.

I'm still stuck. How can I get help?

Please visit the Informatics support form. Ensure you have read all relevant FAQs before continuing.

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