FAQ

Changing the password will affect all services where you login with your U-ID or firstname.lastname (CEN-Useraccounts). If you want to change your UHH or B-Account Password, please have a look at the manual provided by the RRZ.

Information regarding our password policy can be found here.

Linux
If you have access to a linux workstation you can change your passwordopening a terminal and entering the command 'passwd'.

If you can't change you password this way, please try to connect to login.cen.uni-hamburg.de via SSH and run the command here.

Windows
On a windows machine you can press 'CTRL+ALT+DEL' and click on change password...

[Link to this FAQ]

Linux

Use the Login-Server login.cen.uni-hamburg.de to access the CEN network.

Connect to the server via SSH with your u-number and further connect to a different server (e.g. Mistral, Thunder) or your workspace computer (again via SSH).

Windows

To connect to our network please use the program MobaXterm. Our guide can be found here.

[Link to this FAQ]

TeamViewer was replaced in 2020 by the new program "ISL". The functionality remains the same.

ISL allows remote control of any PC using it. We use it to easily help you with problems or to install your desired software.

All windows machines installed by us have ISL pre-installed. It is located under "C:\Program Files\ISL\ISL Light Client".
If ISL is not installed on the machine, download it here (No installation required).

Usage notes:

1. Please close everything personal. We can see your complete screen while remote controlling!
2. Start "ISL Light Client".
3. Check if the box "Allow desktop control" is ticked.
4. We will tell you the connection code via mail or phone.

[Link to this FAQ]

Please check our separate page for printing on PC or Laptop here.

[Link to this FAQ]

If you can not log in to the graphical Linux interface it could be, that your disk quota (maximum size of your profile) has been exceeded.

In order to access your machine, you can change to the text based console (STRG+ALT+F1,....,STRG+ALT+F6). There you can execute the command 'df -h | grep $USER' and check if you exceeded your quota. If the quota is over the limit, you'll have to delete files in order to use KDE or Gnome again. More information about the quota can be found here.

A lot of disk space is frequently used by the .trash directory. This directory is the trashcan and it grows quickly if you never or rarely empty it. How you can identify lage files, you can read in this faq.

After deleting some files you can check again with 'df -h | grep $USER' if you've deleted enough. If the quota is no longer exceeded, you can switch back to the graphical login with 'ALT+F7' and try to login.
If you still can't login or enter the graphical interface, please write a mail to our Helpdesk.

[Link to this FAQ]

There are 4 scenarios for File transfer: Linux -> Linux, Linux -> Windows, Windows -> Windows, Windows -> Linux.

Linux (source):

Windows + Linux (target):

One possible way is to copy your files directly into your home directory. The Home Directory is accessible from Linux and Windows.
You can simply use SCP: scp <files> <U-Account>@login.cen.uni-hamburg.de:~/<target directory> to copy your files (Please change the brackets accordingly).

Linux (target):

If you have a Linux Workstation and it is powered on, you can copy files directly to its /scratch directory. In order to do that, you need the name of your Computer and the path of the desired harddrive. (/scratch/local1/... or /scratch/local2/... etc.)

In order to copy the files you first have to establish a SSH-Tunnel: ssh -L4321:<pc_name>.cen.uni-hamburg.de:22 <U-Account>@login.cen.uni-hamburg.de

After that you can use SCP to copy the files: scp -P 4321 <files><U-Account>@login.cen.uni-hamburg.de:/scratch/local1/<Destination>

Windows (source):

Windows + Linux (target):

You can't copy files directly on your Windows-Workplace, but on the Home-Directory (H).
In order to do that, start WinSCP and connect to 'login.cen.uni-hamburg.de' with your U-ID. You should now be directly inside your Home-Directory. You can also access these files from a linux workspace.

Linux (target):

You can copy files directly to the Harddrive (/scratch) from your Linux workstation. In order to do that you'll can either use an allready established SSH-Tunnel (see establishing a SSH-Tunnel with Putty) or use the more comfortable WinSCP build-in SSH tunnel.

First create a New Site configuration.

• Host name: the fully-qualified name of the destination host (like: cliccs20-l19.cen.uni-hamburg.de)
• User name: your CEN ID starting with u

Further configururations you may find under the advanced tab:

1. first select Advanced
2. next search for Connection -> Tunnel
3. Host name: here use allways login.cen.uni-hamburg.de
4. User name: your CEN ID starting with u
5. at last type your Password (not recommended) or select a private key file (recommended).

Once you store the settings by klicking OK, you are ready to Login to your host.

[Link to this FAQ]

Disk-Quota limits the space in the home directory. In order to see how much of the quota is used, execute the commands in a terminal.

"du -sh ~"

exact occupied space


"df -h | grep $USER"

Filesystem Size Used Avail Use% Mounted on
.../home/cen/<userid> 22G 6.0G 17.0G 27% /home/zmaw/<userid>

Here you can see your hardlimit (Size), your used space (Used) and the available space (Avail). As soon as you are above the softlimit (1GB under hardlimit), you'll receive an email whenever you login reminding you to delete some files. If you exceed your hardlimit or are above the softlimit for more than 7 days, you won't be able to login using the graphical interface(X11). Also some programs (Thunderbird, Firefox bookmarks, settings) won't work and/or generate corrupt files.

In this FAQ you'll find information on how to identify big files.

[Link to this FAQ]

There are several possibilities to identify which data is using the most space.

All of the following commands are valid for your current directory, therefore you should first switch to your home directory using "cd ~".

This command generates a list of your biggest data in Kilobytes in descending order:
du -hs .??* * | sort -hr | more

A more complex method listing the size of your directories (type d):
find . -type d -exec du -ks {} \; | sort -bnk 1
find . -type d -exec du -ks --apparent-size {} \; | sort -bnk 1


A more complex method listing the size of your data (type f):
find . -type f -exec du -ks {} \; | sort -bnk 1
find . -type f -exec du -ks --apparent-size {} \; | sort -bnk 1


"--apparent-size" specifies the apparent size of a file, which can be much larger.

You can also try this method to only list the current active directory (-h stands for human-readable):
du -h --max-depth=1


[Link to this FAQ]

The access to journal-providers are IP-controlled so that you can enter them when you have an IP from within the UHH-network. There are NO PASSWORDS. If you are asked to enter one, you are probably outside the UHH-network.

To still gain access you have several possibilities:

• Connect via SHH to login.cen.uni-hamburg.de and start Firefox there.
• Connect to the Windows terminal server and start Firefox.
• Establish a SSH-Tunnel to a computer within the network and start Firefox there.

[Link to this FAQ]

Problem: when starting firefox you are receiving the following error message: "Firefox is already running but not responding..."

Linux

Check if there is a Firefox/Thunderbird process running
Enter "ps ax | grep firefox" into a terminal and terminate the process using "kill <PID>", e.g. "kill 1234".

If the process is not running the cause might be the ".parentlock"-file. It is located under your profile and has to be deleted.

Note: <CrypticDirectory> has to be replaced with the corresponding name of your directory.

Firefox

~/.mozilla/firefox/<CrypticDirectory>/.parentlock

Thunderbird

~/.thunderbird/<CrypticDirectory>/.parentlock

Windows

Check if there is a Firefox/Thunderbird process running.
Open the task manager (ctrl+alt+delete) and terminate the processes.

If the process is not running the cause might be the "parent.lock"-file. It is located under your profile and has to be deleted.

Note: <CrypticDirectory> and <ACCOUNT> has to be replaced with the corresponding name of your profile and directory.

Firefox

C:\Users\<ACCOUNT>\AppData\Roaming\Mozilla\Firefox\Profiles\<CrypticDirectory>\

Thunderbird

C:\Users\<ACCOUNT>\AppData\Roaming\Thunderbird\Profiles\<CrypticDirectory>\

[Link to this FAQ]

As a user you have access to backups of the last 7 days. To access them and more about the topic "Backup" please check our backup guide (german version).

[Link to this FAQ]

To use Matlab on a mac outside of the institute simply start a ssh-connection and start Matlab with the license server localhost:

• ssh -L 1704:matlab.rrz.uni-hamburg.de:1704 -L 36305:matlab.rrz.uni-hamburg.de:36305 <user>@login.cen.uni-hamburg.de
• matlab.exe -c 1704@localhost

There is a possibility of the following error message appearing when establishing a SSH connection to a Linux machine.

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
96:8f:2e:d1:8c:d3:da:b4:eb:e3:aa:25:ba:bc:a6:d4.
Please contact your system administrator.
Add correct host key in /home/zmaw/[UID]/.ssh/known_hosts to get rid of this message.
Offending RSA key in /home/zmaw/[UID]/.ssh/known_hosts:3
remove with: ssh-keygen -f "/home/zmaw/[UID]/.ssh/known_hosts" -R hostname
RSA host key for data has changed and you have requested strict checking.
Host key verification failed.

*replace [UID] with your u-Number, e.g. u123456.

There are a few reasons for this error:
1. The Hostkey changed because the linux machine was reinstalled. You can delete it with the following command:

ssh-keygen -R <hostname>

2. If the machine was not reinstalled there might be a security flaw.

When in doubt please contact us and tell us the name if the PC (e.g. dell845)

[Link to this FAQ]

You can establish a SSH-Tunnel to access our internal services like the licensing server from outside (at home or on a trip).

These are the steps to creating a connection:

1. Start PuTTY (or download it first at http://www.putty.org/).
2. Open the Menu Connection -> SSH -> Tunnels and enter your preferred service
   
   
   • Matlab: Source port 1704 (License server) and 36305 (Vendor Daemon) - Destination matlab.rrz.uni-hamburg.de:1704
     and matlab.rrz.uni-hamburg.de:36305
   • License Server CEN: Source port 1963 (Depends on the application) - Destination license.cen.uni-hamburg.de:1963
   • License Server RRZ: Source port 27003 (e.g. ArcGIS Pro) - Destination lizenzsrv8.rrz.uni-hamburg.de:27003
     
     
3. Press "add" to add the connection.
4. Switch to "session" and enter the Hostname "login.cen.uni-hamburg.de".
5. Enter a name for your connection.
6. "Open" establishes a connection to the login server. There you have to login using your u-Number.

Additional notes

• For any software requiring a Network license use "localhost" as the server and enter the corresponding port.
  E.g. for matlab: "matlab.exe -c 1704@localhost"

[Link to this FAQ]

To have access "without password" you will need a key pair, consisting of an open and a private part.
Follow these steps to be able to enter your password once and then connect to all linux machines accessing the home directory.

1. Switch to your .ssh Directory
   cd ~/.ssh
2. If you don't have a RSA-key yet, generate one with standard settings:
   ssh-keygen -t rsa
3. Copy the contents and change to strict access rights:
   cat id_rsa.pub >> authorized_keys
chmod 600 authorized_keys
4. Connect to login.cen.uni-hamburg.de via SSH and see if you have to enter your key password.
5. To save your password into the SSH-Agent enter "ssh-add" into the console.

Now you should be able to connect to linux machines without entering your password.

[Link to this FAQ]

The server svn.cen.uni-hamburg.de is only accessible from inside out network. Use a tunnel to connect to it from outside.

Linux

Create a tunnel using:
ssh -L 8080:svn.cen.uni-hamburg.de:443 <userid>@login.cen.uni-hamburg.de

to checkout use the directory
localhost:8080/svn/<repositoryname>

Windows

Please follow the PuTTY installation above and use the Tunnel Configuration
Source port 8080 - Destination svn.cen.uni-hamburg.de:443

After that any SVN-Client will use the following URL for your machine:
localhost:8080/svn/<repositoryname>


Note:

You may receive a SSL-Certificate error because the Certificate is invalid for localhost. You can ignore it.

[Link to this FAQ]

This guide is only used for accessing the WTS within the institure, not remotely!

The Windows-Terminal-Server (WTS) can be used to access e.g. Adobe Acrobat or Microsoft Office on a Linux machine or if the Software is not installed on your local machine.

Linux

Connect using RDP. Open a console and enter
rdp wts.cen.uni-hamburg.de

You can change the resolution with the parameter -g:
rdp wts -g 1280x1024 or
rdp wts -g 90%

Windows

Open the Start menu and enter "Remote desktop" into the search bar, then start the program.
Enter "wts" as the computer name and check if the right user account is used.

[Link to this FAQ]