/etc/ssh/sshd_config HowTo - Linux / Unix Q & A from nixCraft

How to allow root login from one IP address with ssh public keys only

last updated June 10, 2017 in CentOS, Debian / Ubuntu, FreeBSD, Linux, OpenBSD, RedHat and Friends, Suse, UNIX

I am using MacOS on the desktop and Ubuntu Linux on the server. I disabled root login over ssh and enabled ssh based public key login. However, I recently added second Ubuntu server. I need to sync file between two using rsync command. Is there any way that I can log from the second server into my first server with root user from second server IP address only ({root@secondBOX }# ssh root@firstBOX1) without reducing OpenSSH server security option?

How to disable ssh password login on Linux to increase security

last updated January 21, 2018 in CentOS, Debian / Ubuntu, Linux, OpenBSD, RedHat and Friends, Security, Suse

I want to disable ssh clients from accessing using the password and only allow ssh login using SSH keys. How do I disable password authentication for SSH on Linux operating systems?

Linux/Unix: Force ssh client to use only password auth authentication when pubkey auth configured

last updated January 21, 2017 in CentOS, Debian / Ubuntu, FreeBSD, Linux, OpenBSD, RedHat and Friends, Suse, UNIX

I configured and use my openssh server to accept only public key based authentication. I need to test if my server accepting password. How to allow ssh client to use only password auth when pubkey auth configured?

How to change the ssh port on Linux or Unix server

last updated March 19, 2019 in Debian / Ubuntu, FreeBSD, Linux, OpenBSD, RedHat and Friends, Suse, UNIX

I am a new Linux/Unix server admin. How do I change the SSH Port for my Linux or Unix server using command line option?

How to upgrade OpenSSH 7.0 to 7.2 on a OpenBSD Unix and Linux

last updated February 29, 2016 in Linux, OpenBSD, Package Management, UNIX

OpenSSH version 7.2 has been released. How do I install or upgrade my existing OpenSSH version to 7.2 on a OpenBSD unix operating system?

X11 forwarding request failed on channel 0 Error and Solution

last updated March 23, 2014 in Linux, OpenBSD, Troubleshooting, UNIX, X Server

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 1.2.3.4

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

How To Setup SSH Keys on a Linux / Unix System

last updated April 28, 2017 in CentOS, Cryptography, Debian / Ubuntu, Linux, OpenBSD, RedHat and Friends, UNIX

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?