###Basic GNU/Linux/UNIX Command Line Interface (CLI) Utilities###

 tty = reveals current Teletype Terminal (TTY)  w = reveals currently logged-in sessions  ls/dir(alias to ls -l)  ls -lF - returns long format and '/' at the end of directories  ls -lF | grep /  touch - creates empty files / updates time stamps(atime/mtime) on objects  rm - removes objects (files/directories/etc.)  echo - echoes values and variables  echo $? - returns exit status of previously-executed command  set || env - reveals current shell variables  pwd - returns working directory  cd - changes directories; with no options, places us in HOME directory  mkdir - creates a directory  whoami - returns currently logged-in user  su - switches users BASH communicates user-status (privilged/non-privileged) via the prompt:  1. prompt that terminates with '#' reflects 'root' user  2. non '#' prompt indicates non-root user  id - reveals id information (uid,gid,groups)  cp - copies files(files/directories)  mv - moves/renames files, and tries to preserve timestamp  stat - returns properties (size,inode,atime,mtime,ctime,perms,etc.) of files ###SSH-Host-Key### $ cat ~/.ssh/known_hosts 192.168.0.123 ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAr3UN5Kj0qRRzU3M/uZBosBOkH+kDxlD+EwWS10d0fcoVLxuWZUf+XH/9+iib9McQCahjdMY+uoI+JEXMkRO/Xr43wy+1G/IAaQvgJCTQE+jdufUb+zkWxMOUO+muOMMb8I7oORhT1czvagu+7PpICoNESafdctcdSZxmsu2x7RQ17vLQ62HGMaxNCmkOuicSIIpsv8HCT6ISgm+zlVlDaMiRrdOhQRnb3jiLURXq9/d7XTDyjU+rh1fkLW+zIyv9zeXkguvnNxs+LwhJBrKss4ap4BvjbWxs3GCLy72sBuACji6A/Fs/Nud2uluv77FwAKyPshKUeMEPEy/WoGiEjw== $ ls /etc/ssh/*key* /etc/ssh/ssh_host_dsa_key      /etc/ssh/ssh_host_key      /etc/ssh/ssh_host_rsa_key /etc/ssh/ssh_host_dsa_key.pub  /etc/ssh/ssh_host_key.pub  /etc/ssh/ssh_host_rsa_key.pub

IF Host Key changed, you will see this

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @    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 4f:73:ab:5f:a8:62:fd:70:4c:03:53:79:2b:35:13:fe. Please contact your system administrator. Add correct host key in /home/username/.ssh/known_hosts to get rid of this message. Offending key in /home/username/.ssh/known_hosts:1 RSA host key for 192.168.0.123 has changed and you have requested strict checking. Host key verification failed.

to resolve this, just run 'rm -rf ~username/.ssh/known_hosts'