I am a new Linux server user. I need to tunnel X over ssh. I type the following command from OS X Unix terminal to login into far_away_machine (a centos server):

ssh -X -o options -A -p 22 user@centos-far-away-server

But, I am getting the following error on screen:

X11 forwarding request failed on channel 0
Last login: Sun Mar 23 15:58:51 2014 from

How do I fix “X11 forwarding request failed on channel 0″ on Linux or Unix-like systems?


I recently read that SSH keys provide a secure way of logging into a Linux and Unix-based server. How do I set up SSH keys on a Linux or Unix based systems? In SSH for Linux/Unix, how do I set up public key authentication?


I am a new CentOS Linux user. How do I change default sshd tcp port # 22 to 2022 on CentOS Linux version 5/6?


I manage MS-Windows server and recently started to play with OpenBSD server. How do I reload or restart the dhcpd server on OpenBSD using shell command line option?

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I‘m a new Ubutnu Linux user. I backup files to our corporate Unix backup server using the rsync command. The server only allow to upload/download files. I am unable to login to the server. How do change my password using the passwd command over ssh based session?


How do I create and setup an OpenSSH config file to create shortcuts for servers I frequently access under Linux or Unix desktop operating systems?


How do I mount an ISO image in OpenBSD operating systems using command line options?