Remote Access

Goal

You might want to use our pool infrastructure - which means any pool client c001 to c048 - from a remote location, for example from home. This is totally fine!

Strategy

Currently (end of 2015) there are exactly two systems reachable from the outside world:

login.stud.informatik.uni-goettingen.de

usable by every student. The only precondition is that you need to login one time physically on a client before attempting remote access

login.informatik.uni-goettingen.de

usable only by staff members with Gwdg-Account

The login server login.stud.informatik.uni-goettingen.de is meant to be used as a gateway from the outside world to the pool - basically to any computer c001 to c048.

This gateway approach is necessary as the pool computers have local, non-routeable IP-addresses like 172.27.x.y.

For accomplishing access to a pool machine you need to "hop" forward one time. On login you'll see a list of currently running computers. E.g.:

System load of less used clients:
c011          up      16:01,     0 users,  load 0.00, 0.01, 0.05
c018          up      15:46,     0 users,  load 0.00, 0.01, 0.05

Simply jump to any of them. "ssh c011" would work in this example.

Usually the computers in the pool shutdown itself when nobody is logged in. To supply some computers to the above user several pool computers are running continuously to be reachable for this specific use case. This is: c031..c036 which can be found in the first row in room -1.101. These computers are usable locally also without limitation. If they are in use in the very moment when you login remotely they may not be listed as available because of this very fact.

Please note that these clients reboot automatically early in the morning to clean up things - but only if nobody is logged in...

Problems with shared resources

System resources are limited: login.stud.informatik.uni-goettingen.de is a shared source in more intense way than those pool computers are. There is only one single login.stud.

It is considered unfriendly behavior to stress a shared resource in such a manner that other users can not work anymore.

One usual trigger element for this kind or problems is Java.

• Sometimes it crashes and does not clean up the allocated memory nor CPU resources. Just a very few Java processes hanging in the background can render login.stud unusable - it has to get restarted with a hard reset. (Of course other languages allow generating the same problem, but we see Java most of the time...)
• when you use Eclipse you might start background processes. Make sure to stop all of them...

If you have the suspicion that you have produced such background processes do the following:

1. log off
2. go to a normal console - press CTRL-ALT-F2 (or F1/F3/F4/F5/F6)
3. login
4. use top to examine the running processes. For example look for "java" in the "command" column
5. note that the first column shows the process number
6. the single letter "k" (for "kill") will ask you for a process number to be killed. The second prompt will ask for the specific signal to be sent. The default offered is "15/sigterm". If this is not sufficient do the same again and enter "9" which stands for "sigkill".

Problems with X forwarding

tbw

See also

• PuTTY
• FAQ
• Xming