Frequently asked questions
Does the lab have a ...
Video Conference Facility
See the Basic Use Guide.
Yes. Please e-mail sys-admin to be allocated a repository on the UIS Git server.
Subversion repository service
There are two ways to get a local Subversion repository accessible by collaborators:
- For small, short-term collaborations, e.g. to coauthor a paper,
you can grant external collaborators access to a repository in your
normal filespace by configurating your
~/.ssh/authorized_keysfile. Ask each of your collaborators to send you their ssh public key. Add these keys to your
authorized_keysfile as explained in the Subversion book section SSH configuration tricks, namely with a prefix of the form
from="*",command="svnserve -t -r /path/to/repository --tunnel-user=username",\ no-port-forwarding,no-agent-forwarding,no-X11-forwarding,no-pty ssh-dsa AAAABtce9euch...Then tell your collaborators to checkout the URL
man 8 sshd) ensures that your collaborators can only talk to a Subversion server process, can only access the given repository, can only commit under the given username, and can't start a shell. The remaining prefixes disable other
sshfacilities that are not wanted here either. The protection of your personal filespace relies here on the security of the
svnservecommand, therefore such access should only be given temporarily to a very small number of trusted individuals.
- For large collaborations or to grant anonymous access: the department hosts several Subversion servers and repositories on dedicated servers. Additional ones can be requested from sys-admin.
Can I have more quota?
If the request is for a modest increase then the answer will almost certainly be yes. You should make sure you have tidied up things like unpurged deleted mail messages and Firefox cache before you ask.
It may be the case that material does not need to be in backed up filespace — we can offer bulk space on "bigdisc". Although we formally class this as global scratch space, it's actually pretty resilient, being double raid protected in the filer and with the usual snapshots. You may be asked to consider this instead.
There is also local scratch space available on most Unix machines: use
sudo cl-mkscratchdir to
create a filespace in /local/scratch. Local scratch space is not backed up at all, and hence any
deleted files are lost. You should take
care only to use this space for data that you can re-create quite trivially.
For more information on creating and extending scratch space, see Wiki.
I'm leaving the lab, can you keep my filespace/email address/web pages ?
These things are kept for a while by default anyway, we don't delete filespaces on the day that you leave. Your filespace will eventually be archived, but we can forward email indefinitely and set up WWW forwarding if given sufficient information. See Leaving the Computer Laboratory for more information.
I've just accidentally removed a file. Can I get it back?
Probably. See Retrieving lost data for more information.
I can't change my password!
If you get the error message "Token manipulation error" when you try to reset your password from a Linux machine then the most probable cause is that you are not giving a new password of sufficient complexity. Check the rules for password complexity below. If you still are unable to set a password then try to do so on a Windows workstation which should give a more helpful error message.
User passwords must meet the following requirements:
- The password is at least eight characters long.
- The password contains characters from at least three of the following five categories:
- Uppercase letters
- Lowercase letters
- Base 10 digits
- Non-alphanumeric characters
- Unicode characters which are categorized as alphabetic but are neither upper nor lower case (use of these is not recommended)
- The password does not contain three or more sequential characters from the user's account name.
The precise definition of what counts as a letter is documented in detail by Microsoft. Characters outside the ASCII printable set permitted but are best avoided because of the difficulty of typing them on many keyboards.
We recommend that you choose a longer password rather than just using the minimum length necessary. You are unlikely to exceed the maximum permitted length, but some older systems may not accept more than about 28 characters. Around 12 characters is a good compromise between security and convenience.
We do not enforce a regular password change interval, believing that this does more harm than good. However it is important that you change your password if you have any reason to believe that it may have been compromised.
Can I change the default power plan on Windows?
Machines running Microsoft 7 and newer have their power saving option controlled by group policy. The main issue with the power saving mode is if you start a task that cannot be suspended (eg something that requires a network connection to be kept alive), in such cases you may wish to consider setting an alternative power policy which does not sleep. If you do this then please try to use such a setting only when you need it or if you want to use this as your standard setting please try to rember to sleep your machine when you know it is not needed for some time such as at the end of the working day.
Microsoft Dreamspark membership
Microsoft makes selected operating systems and development tools freely available to academic staff and students of the Computer Laboratory, under the Microsoft Dreamspark for Academic Institutions programme. You will receive the account details needed by e-mail in the Michaelmas term after arrival. This email is send from the hosting institution so may be classified as spam.
Please ensure you keep a record of all licenses issued to you, as they cannot be retrieved after you leave the department.
This scheme does not cover Microsoft Office and is not available to students from other departments or faculties.
The network and connections
Can I attach my own (or a visitors) machine to the Department's network?
Possibly, but only if you are a member of staff or a research student and only subject to certain rules. For more information, see The CL network.
I can't connect to a host address or, what does strict checking mean ?
This question is usually in response to a message from
ssh like this:
No RSA host key is known for "host address" and you have requested strict checking. Host key verification failed.
and you are not offered the chance to accept the key on the basis of the fingerprint.
The purpose of the strict checking is to make sure that the host really is the expected one, and that there isn't a man-in-the-middle compromise. You need some way to make sure that the public key is that of the ACTUAL machine. If you can get the system administrator at that address to mail you the fingerprint or key in such a way that you trust the information, use that.
Otherwise, the best bet is probably to login using your user key if it is already installed (you may be able to get the system manager to do this for you) using
slogin -o StrictHostKeyChecking=ask $host
and making sure that it really is the machine you expect. Something like
ssh-keygen -l -f /etc/ssh/ssh_host_rsa_key
should confirm the fingerprint you just received.
In general, if you have a problem connecting to a host using
ssh and need to ask
us for assistance, please try using
ssh -v hostname, which causes
ssh to print
debugging messages about its progress. You should then cut & paste the result
into your email message asking us for help.
For more information, see SSH access to the CL systems.
Can I have piece of software X installed on my lab-managed linux box ?
Where is java/javac ?
Machines usually have java installed when they are set up, and have the version of the jre installed that is appropriate at the time. Thus we have a mixture of versions on different machines, and sometimes more than one version. Whatever the version it will be placed in a subdirectory of /usr/java, so that is the first place to look. The RPMs we install from do not always place links in /usr/bin, so you may have to add the /usr/java/some-version-of-the-jre/bin directory to your PATH.
You may not have the java compiler installed by default (if you do it will also be in some subdirectory of /usr/java), in which case you may be able to install it yourself. See Can I have piece of software X installed on my lab-managed linux box ? and look for the jdk bundle.
I'm having difficulty finding Open Office ?
Unfortunately the name of Open Office executables seems to be different on and within each Operating System distribution. There is a local wrapper script called soffice which tries to hide these differences and find a suitable executable, use that instead.
Why am I told Firefox is running, when its not?
Every time you click on the shortcut to launch Mozilla Firefox, you get a pop-up message box saying:
"Firefox is already running, but is not responding. To open a new window, you must first close the existing Firefox process, or restart your system."
The cause seems to be a .parentlock file which has remained locked after a crash, preventing further use of the application. You need to remove this file (which resides in the .mozilla folder in your home folder) to get back up and working again.
How can I put files on the Lab web server?
For your personal web space, see Personal web pages, but you should remember that when you leave the lab, this must either be removed or redirected to another private web space elsewhere. For anything that should remain in the lab after you have gone, you will need a directory elsewhere in the server. Most research groups already have a suitable area and somebody looking after it, so talk to them first. If you have something which does not seem to fit in any existing structure, you should contact pagemaster for advice.
How do I run CGI, PHP or similar scripts on the Lab web server?
Unfortunately you cannot do this on the main lab server. The lab web server is a mission critical server and we cannot allow user-written code to run on it. Scripts may introduce security holes, or simply consume excessive resources. However, there is a separate server www-dyn.cl.cam.ac.uk that only has access to a small part of the departmental file server and where CGI and PHP scripts can be executed.
Can I run my own web server?
A web server is just a program, and any machine can run one, though it may not be possible to bind to port 80. Such a server will be available inside the department but will not be accessible from the outside. If you have a genuine need to make a private web server publicly accessible, you should discuss your requirements with webmaster well in advance. Any externally open server is a potential security risk, and moreover any web server becomes part of the public face of the department. These considerations mean that we need to take some care over what is exposed to the outside world.