Frequently Asked Questions: Managing Your Account
How do I change my password?
Log in to the SRCF server and issue the command yppasswd — you will be prompted for your old password before being asked to give the new one twice. Make sure that your choice of password is secure — don't use dictionary words, names or anything else which can be associated easily with you (such as a phone number or car registration number), and please don't use simple substitutions (e.g. using “f15hcake” instead of “fishcake”) as these can be easily guessed. The best passwords are collections of random letters and numbers, which you can remember by inventing a simple mnemonic. The command apg can be used to suggest good passwords.
If you don't understand all of that, or have forgotten your old password so you can't log in, you can email email@example.com and we'll give you a new random password.
Can I tell my friend my password so that he can help maintain my website?
You are the only person authorised to use your password. If we find any evidence that it is being used by someone else then your account will be suspended indefinitely and without notice.
If you would like to run a website which is maintained by several people then you should apply for a group account.
If you suspect that someone else knows your password, please change your password immediately and notify firstname.lastname@example.org.
What is SSH and why should I use it?
SSH is a remote login protocol similar to telnet, but which uses encryption to prevent eavesdropping. If you use telnet to log into any machine, it is trivial for a cracker to obtain your password from any machine on any of the networks between you and the remote machine - with SSH this is not the case. We therefore require you to use SSH to connect to our systems.
What's your view on world writable files?
World writable files are files that anybody on the system can write to (edit). Whilst in general you can trust other SRCF users not to modify your files, there are several reasons why world-writable files are a problem:
- People make mistakes. For instance, if you have a world-writable directory, and somebody runs "rm -r /" by mistake (this has happened at least once) then all the files in that directory will be deleted.
- Users' accounts may have been compromised. We have had one incident where a worm entered the computer via an insecure society website and proceeded to overwrite every world-writable file on the computer.
- World writable files make things easier for attackers. If for instance a directory underneath your public_html directory is world-writable then an attacker able to write files on the system could place a script there containing commands that he could execute as you.
To avoid problems like this we recommend that you avoid creating world-writable files and directories, and if you have created them then you change them to be non-world-writable. You can do this using the "chmod" command - "chmod o-w filename" will remove world-writable permissions from a file and "chmod -R o-w ~" will do the same for all world-writable files in your home directory.
Some cgi scripts will tell you that they need to have world-writable files / directories to work. This is almost certainly not the case on the SRCF system where cgi / php scripts run as the user that owns them rather than the webserver. For society accounts it is often necessary to make the files group-writable rather than world-writable (presuming that the intended effect is to allow multiple members of the society to write to them). If you can't get a script to work without world-writable files / directories then get in touch with email@example.com and we'll see what we can do to help.
I can see everybody's files!
This is the way it's supposed to be - on UNIX (and UNIX-like) systems users can see all of each others' files by default (as UNIX was designed for use in an academic environment to make sharing work etc. easier). It is possible to remove the "world readable" setting from files (log in on the command prompt and run chmod o-rwx 〈filename〉"), and you should do that with files containing passwords. Similarly, you can create a directory (perhaps called “private”) use the same command to stop other users accessing it. It's not a good idea to make your whole home directory private as some programs (such as the web server) need to see files inside it.
Other security issues
As well as keeping your password safe, you also need to make sure that any additional software that you install is secure. Exploiting a vulnerability that allows an attacker access either to your account or that of a society user is often the first step in getting administrative access to the machine. This is particularly true for PHP and CGI scripts used on your website, but any software may be affected. Please take into account the following when installing software of your own:
- If there is a suitable piece of software in the stable Ubuntu release then ask us to install it centrally rather than installing your own copy. Centrally installed software gets upgraded automatically when security patches are released. You can search for Ubuntu packages at http://packages.ubuntu.com/.
- Use existing software rather than writing your own, especially if there is an existing piece of software which is popular and has a strong community of users.
- Make sure you install security patches as soon as they are released. Google makes it very easy for attackers to find their targets once a vulnerability is known.
- Subscribe to the announcement mailing list associated with the software you install, so that you find out quickly about any security issues.
If you do suspect that an attacker has obtained access to your account, please let us know immediately so that we can make sure that they haven't made changes to the system. Remember, if an attacker successfully gains access, it may result in several days of downtime not just for your website, but for everyone who uses the machine.
What happens to my account when I graduate?
You continue to be a member of the SRCF for life. As long as you are contactable by email, your account will remain active. Note this means you will likely have to change your address from @cam.ac.uk to something else when you graduate. Contact the sysadmins at firstname.lastname@example.org to do so.
What is the full path to my filespace?
Personal filespaces are kept in the /home/ directory, for example /home/abc45/. Society filespaces are in /societies/, for example /societies/foosoc/. Although we try to minimise the number of changes to the filesystem, we cannot guarantee that this will always be the case. We therefore recommend that you avoid using absolute paths wherever possible, such as by using relative paths instead. If this is not possible, we recommend that you make it easy for you to change the location of your files, e.g. by setting things up so that file locations can be specified in configuration files.
How do I find out how much of my quota I have used?
Simply log in and use the command:
Note that the -g is required as our disk usage quotas are managed on a per-group rather than per-user basis, with each user having their own group.
I've run out of quota — Can I get it increased?
Our initial quota of 2 GB is deliberately set relatively low to reduce the risk of users accidentally filling the disk (this is surprisingly easy to do, for example with log files). If you would like more and have good reason then just ask the sysadmins and we'll increase it for you. Note that while disk space is cheap, we need to supply it four times over (as we use RAID). More disk space also tends to mean more bandwidth, and other problems associated with running a larger server, so please be considerate in your disk usage. If you need a lot more resources we may ask you to consider making a donation towards the costs of running the server.