Tag: openssh

Apple OS X: Install X Window System XQuartz For SSH X11 Forwarding On a Mavericks or Yosemite

Posted on in Categories , , , , last updated May 5, 2015

I need to tunnel X Window securely over SSH bases session so that I run X program on my remote Linux/Unix server/workstation and get back display to my Apple Macbook pro laptop. I tried the ssh -X user@server1 and ssh -Y user@server2 commands on both OS X Mountain Lion and Apple OS X Mavericks/Yosemite. But, I am unable to use the ssh command with X11.

How do I fix this problem on OS X and enable X11 forwarding with ssh command? How do I install XQuartz (X11.app) server on Apple OS X Mountain Lion or Mavericks or Yosemite?

HowTo: Revoke OpenSSH Keys and Disable User Access

Posted on in Categories last updated November 6, 2012

Many users are using ssh to log into a remote machine and append the indicated identity file to machine’s ~/.ssh/authorized_keys file. I recently moved one of my server, and I would like to revoke openssh keys and disable user access under Linux operating systems. How do I revoke OpenSSH keys under Unix or Linux operating systems?

Linux / Unix: Disable OpenSSH Host Key Checking

Posted on in Categories last updated December 30, 2011

I‘ve a remote Unix server running with OpenSSH remote login service. The openssh is configured for passwordless login using ssh keys. Our ISP allows to boot all Linux servers into the rescue mode. It allow us to bring a server online remotely in order to troubleshoot system problems that would normally only be resolved by an OS Reload (such as accidentally deleting files or wrong firewall configurations blocking ssh access). When server boots into a remote rescue mode I can connect using SSH. They SSH keys will not be the same in the rescue mode so I get key mismatch messages as SSH keys are re-generated on each boot:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that the RSA host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
e1:9b:5c:16:a6:cd:11:10:3a:cd:1b:a2:16:cd:e5:1c.
Please contact your system administrator.
Add correct host key in /home/user/.ssh/known_hosts to get rid of this message.
Offending key in /home/user/.ssh/known_hosts:1
RSA host key for www.cyberciti.biz has changed and you have requested strict checking.
Host key verification failed.

How do I ignore OpenSSH hos key checking from my Apple OS X laptop while login using the ssh?

OpenSSH Hide Version Number From Clients

Posted on in Categories last updated September 13, 2010

How do I hide ssh number from clients? When I type the following command it displays server version number to end users:

ssh -v server2.example.com

OpenSSH_5.3p1 Debian-3ubuntu4, OpenSSL 0.9.8k 25 Mar 2009
debug1: Reading configuration data /home/vivek/.ssh/config
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to server2.example.com [123.x.y.z] port 22.
debug1: Connection established.
debug1: identity file /home/vivek/.ssh/identity type -1
debug1: identity file /home/vivek/.ssh/id_rsa type 1
debug1: Checking blacklist file /usr/share/ssh/blacklist.RSA-2048
debug1: Checking blacklist file /etc/ssh/blacklist.RSA-2048
debug1: identity file /home/vivek/.ssh/id_dsa type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_4.3
debug1: match: OpenSSH_4.3 pat OpenSSH_4*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.3p1 Debian-3ubuntu4

OR

telnet server2.example.com 22
Trying 123.x.y.z...
Connected to v.txvip1.
Escape character is '^]'.
SSH-2.0-OpenSSH_4.3

Why does OpenSSH server report its version to clients?