Linux / UNIX: Speed up SSH X11 Forwarding

I‘ve an CentOS based server and Ubuntu based desktop pc. I’m connecting to my CentOS using ssh X11 forwarding feature. However, speed over the Internet is pretty slow for certain apps such as VMWare console. How do I speed up OpenSSH X11 forwarding using Linux / UNIX desktop system?

You need to use the following syntax to speed up SSH 11 forwarding:

ssh -X -C -c cipher1,cipher2


  • -X : Turn on SSH X11 forwarding
  • -C : Requests compression of all data. You can also specifies the compression level to use if compression is enabled using the CompressionLevel option in ssh_config file. The argument must be an integer from 1 (fast) to 9 (slow, best). The default level is 6, which is good for most applications.
  • -c : Set ciphers. Blowfish is a fast block cipher; it appears very secure and is much faster than 3des. (see sshd man page for more info).

In this example, connect to the ssh server called using vivek user and start firefox browser:
$ ssh -X -C -c blowfish-cbc,arcfour
[www544 ~] $ firefox &

You can avoid typing by editing /etc/ssh/ssh_config file as follows:

Cipher blowfish
# default line 
##Ciphers aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc
## see man page for more info on Ciphers 
Ciphers blowfish-cbc,aes128-cbc,3des-cbc,cast128-cbc,arcfour,aes192-cbc,aes256-cbc
Compression yes

Save and close the file. You can now simply connect it as follows:
$ ssh -X
[www544 ~] $ firefox &


  • man pages – ssh, ssh_config, sshd

Posted by: SXI ADMIN

The author is the creator of SXI LLC and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

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