Ssh

Installing SSH

Make sure you have openssh-client installed you might already have it installed if not do

sudo apt install ospenssh-client

to install openssh-server do

sudo apt install openssh-server

You need to edit the file located in /etc/ssh/sshd_config you can either cd into each directory until you get to the file or simply do

sudo vim /etc/ssh/sshd_config

You will want to change the default port to something else besides 22 you can do this by removing the # and entering the number you want

Change PermitRootLogin prohibit-password → PermitRootLogin no

You can choose to allow only users you specify by adding AllowUsers (user) at the end of the file

You can do groups instead if you'd like by doing AllowGroups (group)

To add a user to that group do sudo usermod -aG (group) (user)

the -a to add and the -G is used for secondary group to change a users primary group do just -g.

To create groups do

sudo groupadd (groupname)

To delete a group do

sudo groupdel (groupname)

To generate a new key do

ssh-keygen

Two new files will be created in .ssh id_rsa and id_rsa.pub

In order to create a public key relationship between two systems do

ssh-copy-id -p(port) -i ~/.ssh/id_rsa.pub (ip)

once the key is copied over a new file called authorized keys should appear under .ssh on the second machine.

You can turn PasswordAuthentication no in config file

First ask person that is ssh'ing into the server to add -v which is verbose. (client side)

ssh -v user@host

If you want to see logs in Ubuntu/Debianon your side do (server side)

cat /var/log/auth.log

If you want to see the last 10 lines of log file do

tail /var/log/auth.log

If you want too see log in real time do

tail -f /var/log/auth.log