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Asked: 2024-09-24T07:21:14+05:30 In:

How can I restrict the maximum number of concurrent SSH connections for users on my Ubuntu server? I want to ensure that no more than a specified number of SSH sessions can be open at any time. What steps should I take to implement this?

I’ve been battling with user connections on my Ubuntu server lately, and I figured it’s time to tighten things up a bit. Specifically, I want to restrict how many SSH connections can be made at the same time for individual users. You know, to avoid one user hogging all the juice and leaving everyone else out in the cold.

I’ve done a bit of digging, and I believe there are ways to manage this, but I’m not quite sure of the best approach or the steps I should take. I’ve seen some folks mention using the “MaxSessions” setting in the SSH configuration file, but I’m a bit hazy on how exactly that works. Then there’s talk about using “pam_limits” — does that really help in this case?

I suppose I’m looking for a step-by-step guide or some tips on how to implement this without accidentally locking myself out of my own server! Like, what file do I need to edit? Is it just SSH config, or will I have to tweak other settings too? And I’d love to know if there are any common pitfalls I should avoid here, like accidentally restricting myself or causing issues for other valid users.

Also, are there any best practices when it comes to numbers? Like, how many connections are reasonable before the server starts to feel the strain? I want to strike a balance between security and accessibility since I do have a couple of users who rely on the server for various tasks.

If someone could share their own experience or a detailed walkthrough on how I can limit the number of concurrent SSH connections per user efficiently, I’d really appreciate it. Any suggestions for troubleshooting if things don’t go smoothly would be golden too! Thanks in advance for any help!

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    1. Limiting SSH Connections on Ubuntu


      How to Limit SSH Connections on Ubuntu

      To keep things in check and avoid one user hogging all the SSH connections, you can use a couple of methods to set some limits. Here’s a simple guide!

      Method 1: Edit SSH Configuration

      You can use the MaxSessions setting in the SSH configuration file. Here’s how:

      1. Open the SSH configuration file:
   sudo nano /etc/ssh/sshd_config

2. Look for the line that starts with #MaxSessions. If it's commented out, uncomment it and set it to your desired limit, like this:
   MaxSessions 2

   This allows 2 concurrent sessions per user.

      After that, save and exit the file. Then, restart the SSH service to apply the changes:

      sudo systemctl restart sshd

      Method 2: Use PAM Limits

      The pam_limits module is another way to control user limits.

      1. Open the limits configuration file:
   sudo nano /etc/security/limits.conf

2. Add a line for your user (or use * for all):
   username hard maxlogins 2

   Replace username with the actual user's name. This limits them to 2 concurrent logins.

      Then save and exit. You might want to log out and back in for the changes to take effect.

      Common Pitfalls

      • Be careful not to lock yourself out! Always make sure to test the changes with a separate session if possible.
      • Check if your user is part of a group that needs a different limitation. You can use the group name instead of the username.

      Best Practices

      As for numbers, consider how many simultaneous users you have. Generally, 2-3 concurrent connections per user is reasonable for most use cases, but adjust as per performance. Monitor your server to see how it handles your traffic.

      Troubleshooting Tips

      If things don’t go as planned:

      • Check the SSH logs for errors using tail -f /var/log/auth.log.
      • Ensure your syntax is correct in configuration files—one typo can mess things up!
      • Try connecting from another session if you get locked out. You can always revert changes if needed.

      Keep in mind that you can always reach out for more help if you run into issues. Good luck managing those SSH connections!



    2. To restrict the number of concurrent SSH connections per user on your Ubuntu server, you can use the “MaxSessions” directive in the SSH configuration file, typically located at /etc/ssh/sshd_config. This directive limits the maximum number of open sessions permitted per network connection. For example, to allow a maximum of 2 sessions per user, you would update the configuration file as follows: MaxSessions 2. After making this change, remember to reload the SSH service to apply the settings: sudo systemctl reload sshd. Additionally, you might consider using PAM (Pluggable Authentication Module) to set user-specific connection limits. This involves editing the /etc/security/limits.conf file and adding lines like username hard maxlogins 2 to limit a specific user to a set number of logins.

      Be cautious while making these changes to avoid locking yourself out. It’s advisable to maintain an active SSH session while testing your modifications to the configuration files. Links such as pam_limits can help manage resource limits effectively, but ensure that the user you are logged in as does not get restricted inadvertently. As for best practices, the optimal number of concurrent sessions depends on your server’s specifications and expected load; generally, limiting users to 2-4 concurrent sessions is a good start. Monitor your server’s performance after implementing these limits and adjust as needed based on actual usage patterns, ensuring a balance between security and accessibility for your users.


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