WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!

When you try to connect to a remote server via ssh and you receive the message:

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    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 a host key has just been changed.
The fingerprint for the RSA key sent by the remote host is
SHA256:shacode.
Please contact your system administrator.
Add correct host key in /Users/username/.ssh/known_hosts to get rid of this message.
Offending RSA key in /Users/username/.ssh/known_hosts:21
RSA host key for IP_ADDRESS has changed and you have requested strict checking.
Host key verification failed.

you can reset the known_host for the ip_address with the command:

ssh-keygen -R <hostname or ip_address>

the -R hostname Removes all keys belonging to hostname from a known_hosts file.

sudoers grant

For grant sudoers to user in redhat, centos, oralce linux, edit the file /etc/sudoers and append
username ALL=(ALL) ALL
under
root ALL=(ALL) ALL

For example:

## Next comes the main part: which users can run what software on
## which machines (the sudoers file can be shared between multiple
## systems).
## Syntax:
##
##     user    MACHINE=COMMANDS
##
## The COMMANDS section may have other options added to it.
##
## Allow root to run any commands anywhere

root    ALL=(ALL)     ALL
oracle    ALL=(ALL)     ALL

less command

The navigation keys in less command are similar to Vim editor.

Forward Search

    / – search for a pattern which will take you to the next occurrence.
    n – for next match in forward
    N – for previous match in backward

Backward Search

    ? – search for a pattern which will take you to the previous occurrence.
    n – for next match in backward direction
    N – for previous match in forward direction

For viewing large log files

    CTRL+F – forward one window
    CTRL+B – backward one window
    CTRL+D – forward half window
    CTRL+U – backward half window
    j – navigate forward by one line
    k – navigate backward by one line
    G – go to the end of file
    g – go to the start of file
    q or ZZ – exit the less pager

Useful other command

    v – using the configured editor edit the current file.
    h – summary of less commands
    &pattern – display only the matching lines, not all.

File paging
You can open multiple files by passing the file names as arguments:

$ less file1 file2

virtualbox: mount shared esterno su linux

You have to specify the path and folder to share with the service name on virtualBox

for the mount you can use this command:

sudo mount -t vboxsf nome_servizio /shared_name

you need on your linux OS one folder (mkdir shared_name)

for example if the service name is “stage” and the folder name on the system is shared you can use this command:

sudo mount -t vboxsf stage /shared

for the unmount you can use:

sudo umount -t vboxsf stage /shared