openssh HowTo - Linux / Unix Q & A from nixCraft

Ubuntu Linux install OpenSSH server

last updated August 17, 2018 in OpenBSD, Ubuntu Linux

How do I install OpenSSH server on Ubuntu Linux?

How to exclude file when using scp command recursively

last updated December 29, 2017 in FreeBSD, Linux, OpenBSD, UNIX

I need to copy all the *.c files from local laptop named hostA to hostB including all directories. I am using the following scp command but do not know how to exclude specific files (such as *.out):
$ scp -r ~/projects/ user@hostB:/home/delta/projects/
How do I tell scp command to exclude particular file or directory at the Linux/Unix command line?
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How to use/run bash aliases over ssh based session

last updated December 26, 2017 in BASH Shell, Linux, OpenBSD, Troubleshooting, UNIX

I have set up a bash alias named file_repl. It works entirely when I log in using ssh command. However, my bash aliases are not running over ssh, for example:
$ ssh vivek@server1.cyberciti.biz file_repl bash: file_repl: command not found
How do I run bash shell aliases when I use ssh command?

How to fix: MacOS keep asking passphrase for ssh key after upgrade or reboots

last updated January 17, 2017 in Mac OS X, OpenBSD, UNIX

I recently upgraded my MacOS Sierra and now ssh command keep asking for passphrase as follows when I try to login to my remote Linux/Unix server:
Enter passphrase for key ‘/Users/vivek/.ssh/id_ed25519’:
How do I fix MacOS Sierra upgrade that keep breaking ssh keys in terminal?

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

last updated May 5, 2015 in Mac OS X, OpenBSD, Package Management, Troubleshooting, UNIX

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?

Linux / Unix ssh-keygen: Create A Host Key File

last updated October 29, 2012 in OpenBSD, UNIX

How do I create a host key file to use with my applications as I can not use system defined /etc/ssh/ssh_host_rsa_key for non-root account under Linux / Unix / Apple OS X / *BSD operating systems?

HowTo: Revoke OpenSSH Keys and Disable User Access

last updated November 6, 2012 in UNIX

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?