DoC Computing Support Group

Authentication: Passwords

Single Sign On (Kerberos)

We are aiming towards a single College password for each user, that allows you to access all standard university and Departmental services, such as email, remote login and web services. Currently, all CSG-maintained Linux systems in the Department will accept


  • your College password (actually a Kerberos password stored in the College Active Directory domain),


  • your DoC Kerberos password (if you've been at DoC for at least 5 years, and if your doc password was not been deactivated (for instance, in Feb 2011).

DoC Windows machines currently use their own separately-stored passwords - however changing your College password via ICT's password change webpage attempts to also set your DoC Windows password.

So usually, your College and DoC Windows passwords will be the same. Sometimes the synchronization fails (we're working on this), and you may need to manually change your DoC Windows password to the same as your College password.

Kerberos also provides the ability to use ticket-based automatic single sign-on across services that have been extended to support it. When you login to (or unlock a locked session on) a DoC Linux machine, you receive a Kerberos ticket that lasts 8 hours. All the following services will try your current ticket rather than asking you for your password again until your ticket expires after 8 hours:

  • Remote login via Secure Shell (SSH);
  • Departmental web pages accessed over HTTPS from Kerberos-aware browsers like Firefox;
  • Network filesystem access via Windows Networking (SMB/CIFS) - but this uses your DoC Windows AD/Kerberos ticket.

When your ticket has expired, you can give yourself another ticket from the College Kerberos/AD servers either by screen locking and unlocking your Linux session, or via the Linux command:

kinit xyz13@IC.AC.UK

[if your username is xyz13].

Note that "IC.AC.UK" must be written in upper case as shown, it's not an email address, it's a Kerberos realm. If you're having trouble logging in to any service, this is a really good test command to run, as it provides specific error messages in the event that something unusual has happened, such as your account being locked.

Changing your College Password

Assuming that you know your current College password, you can change your College password either by:

kpasswd xyz13@IC.AC.UK

Please note that College passwords must be changed at least once a year, if you receive an email saying you need to change your College password in the next few days, take it seriously and do so. Do not ignore it or your account will get locked out and you will need to visit the ICT Service Desk in person to get it unlocked.

Changing your DoC Kerberos password

If you still have a vestigial DoC Kerberos password set, you can change it from the Linux command line:

kpasswd abc02@DOC.IC.AC.UK

Changing your DoC super-user password

If you have been granted super-user access to a machine, you will have a 'root principal' with a different password to your main accounts. You can change it from the Linux command line:

kpasswd xyz13/root@DOC.IC.AC.UK

Changing your DoC Windows password

Assuming that you know your current password, either:

  • Log in, press CTRL-ALT-DELETE, and select 'Change password'.
  • from the Linux command line:

kpasswd xyz13@WIN.DOC.IC.AC.UK

If you can't remember your password

If you can't remember your College password, choose from these options:

  • come to CSG (room 225 Huxley) with your swipe card and ask us to let you change it.
  • go to the ICT service desk (level 4, Sherfield) and ask the same.
  • email (eg. when abroad) and plead insanity. provide sensible info, eg. your username, your CID and they'll usually take pity on you..

  • contact the ICT service desk on x49000 (i.e. 0207 594 9000) and plead insanity again.

If you can't remember one of your DoC passwords, come to CSG (room 225 Huxley) with your swipe card and ask to let you change it.


services/authentication (last edited 2015-11-01 16:56:46 by ldk)