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TROUBLESHOOTING: When students cannot log in to the LESBOS server

You cannot log in to lesbos.ccg.uni-koeln.de? In most cases the cause is one of the issues listed below. Please go through the list in order before contacting us.

Quick navigation
Check username Check public key Permissions SSH command Private key Re-add the key

1. Check the username

  • Is the username exact (watch out for upper/lower case)?
  • Does the home directory exist at /home2/<username>?

2. Check the public key on the server

File on the server:

/home2/<username>/.ssh/authorized_keys
  • Is the correct key listed?
  • No line breaks or extra characters?

3. Check permissions

Run on the server (as administrator):

chmod 700 /home2/<username>/.ssh
chmod 600 /home2/<username>/.ssh/authorized_keys
chown -R <username>:students /home2/<username>/.ssh

4. Correct SSH command

From the client:

ssh -i ~/.ssh/lesbos_<username> <username>@lesbos.ccg.uni-koeln.de -p 22

5. Frequent errors

Does the private key exist on the student's machine?

  • macOS / Linux: ~/.ssh/
  • Windows PowerShell: C:\Users\<Name>\.ssh\
  • Windows Git Bash: ~/.ssh/
  • Windows WSL: ~/.ssh/

If the private key is missing, a new key pair must be generated (see Access to LESBOS server).

The most common mistakes in the SSH command:

  • -i is missing → no private key is used.
  • Wrong key name → e.g. lesbos_sg01 instead of lesbos_<username>.
  • Key in the wrong folder → not in the ~/.ssh/ directory.

6. Re-add the public key

If the steps above do not help:

  1. Add the new .pub file to the server's authorized_keys.
  2. Then ask the student to test again.

7. Still not working?

Please send an e-mail with the following details to k.t.nguyen [at] uni-koeln [dot] de:

  • First and last name, UniLogin, study programme
  • Course (e.g. »Bio V SoSe 2026«)
  • Operating system and version (e.g. »Windows 11 23H2«)
  • SSH client and version (e.g. »WinSCP 6.3«)
  • The exact error message (screenshot or text snippet – please do not include any passwords!)
  • When the error first occurred and whether it had worked before
Related guides
LESBOS access SSH setup (WinSCP / Cyberduck) University of Cologne VPN ← Back to Teaching