4 Ways to Speed Up SSH Connections in Linux

If you use Linux for remote access to other servers or devices, you are likely familiar with SSH (Secure Shell) protocol. SSH is a network protocol that enables secure data communication over an unsecured network. However, sometimes SSH connections can be slow, and that can be frustrating. In this article, we will look at four ways to speed up SSH connections in Linux.

Use Compression

Compression is a method of reducing size of data transmitted over network. It can significantly improve speed of SSH connections, especially over slow or high-latency networks. To enable compression, you need to add following line to your SSH configuration file −

Compression yes

This line tells SSH to enable compression for all data sent over network. You can also set compression level by adding following line to your SSH configuration file −

CompressionLevel 9

The compression level ranges from 1 to 9, with 1 being fastest and 9 being slowest but most efficient. You can experiment with different compression levels to find one that works best for your network.

Use ControlMaster

ControlMaster is a feature of SSH that allows you to reuse an existing SSH connection to speed up subsequent connections. When you use ControlMaster, SSH sets up a single master connection to remote host and uses that connection for subsequent connections to same host

To enable ControlMaster, you need to add following lines to your SSH configuration file −

ControlMaster auto
ControlPath ~/.ssh/sockets/%r@%h-%p

The first line tells SSH to use ControlMaster for all connections, and second line specifies path to control socket. You can customize path to control socket if you prefer.

Once you have enabled ControlMaster, SSH will reuse master connection for subsequent connections to same host, which can significantly improve speed of your SSH connections.

Use a Faster Cipher

A cipher is a method of encrypting data transmitted over network. SSH supports several ciphers, but some ciphers are faster than others. By using a faster cipher, you can improve speed of your SSH connections.

To specify a faster cipher, you need to add following line to your SSH configuration file −

Ciphers aes128-ctr,aes192-ctr,aes256-ctr

This line specifies three fast ciphers − aes128-ctr, aes192-ctr, and aes256-ctr. You can also remove any slow ciphers from list to further improve speed of your SSH connections.

Use Multiplexing

Multiplexing is a feature of SSH that allows you to reuse an existing SSH connection for multiple sessions. When you use multiplexing, SSH sets up a single connection to remote host and uses that connection for multiple sessions.

To enable multiplexing, you need to add following lines to your SSH configuration file −

ControlPath ~/.ssh/sockets/%r@%h-%p
ControlMaster auto
ControlPersist 600

The first line specifies path to control socket, second line enables ControlMaster, and third line specifies time to keep master connection alive after last session has ended. In this example, master connection will be kept alive for 10 minutes (600 seconds) after last session has ended.

Once you have enabled multiplexing, you can open multiple SSH sessions to same host without setting up a new connection each time, which can significantly improve speed of your SSH connections.

Here are some additional tips you can try to further optimize your SSH connections in Linux −

Use a Faster Network

One of the main factors that can impact SSH performance is network latency. If you're accessing a remote server over a slow or congested network, your SSH connections may be slow as well. To improve performance, you may want to consider optimizing your network or upgrading to a faster network connection.

For example, if you're using a wireless network, you may want to switch to a wired connection instead. This can help reduce latency and improve stability, which can in turn improve SSH performance.

Use SSH Agent Forwarding

SSH agent forwarding is a feature that allows you to use your local SSH agent to authenticate to remote servers. This can help speed up your SSH connections by avoiding the need to enter your password each time you connect to a remote server.

To enable SSH agent forwarding, you'll need to add the following lines to your SSH configuration file −

Host *
ForwardAgent yes

Once you've made these changes, you can establish a new SSH session with agent forwarding enabled −

ssh -A username@hostname

This will allow you to authenticate to remote servers using your local SSH agent, which can speed up your connections and make it easier to manage multiple servers.

Use SSH Connection Sharing

SSH connection sharing is a feature that allows you to share a single SSH connection between multiple processes. This can help reduce the time it takes to establish new SSH connections and improve overall SSH performance.

To enable SSH connection sharing, you'll need to add the following lines to your SSH configuration file −

ControlMaster auto
ControlPath ~/.ssh/sockets/%r@%h-%p
ControlPersist 600

Once you've made these changes, you can establish a new SSH session with connection sharing enabled −

ssh -o ControlMaster=auto -o ControlPath=~/.ssh/sockets/%r@%h-%p username@hostname

This will allow you to reuse an existing SSH connection for new SSH sessions, improving performance and reducing resource usage.

Conclusion

SSH is a powerful tool for remote access to other servers or devices, but slow connections can be frustrating. By using compression, ControlMaster, a faster cipher, and multip lexing, you can significantly improve speed of your SSH connections in Linux. These methods are easy to implement and can make a big difference in your productivity.

It's worth noting that effectiveness of each of these methods will depend on your network setup and specific circumstances of your SSH connections. Therefore, it's a good idea to experiment with different settings to find ones that work best for you.

Finally, it's essential to ensure that you're using latest version of SSH, as newer versions often come with performance improvements and security enhancements. You can check your SSH version by running following command in your terminal −