SSH

Question 1

What is the command to install ssh?

Answer 1

apt-get install openssh-server

Question 2

What is the command to check if the status of the ssh service?

Answer 2

service sshd status

systemctl status sshd.service

Question 3

What is the command to start the ssh service?

Answer 3

service sshd start

systemctl start sshd.service

Question 4

What is the command to stop the sshd service?

Answer 4

service sshd stop

systemctl stop sshd.service

Question 5

What is the command to ssh into another machine?

Answer 5

ssh user@hostname

Question 6

What is the command to generate public/private keys?

Answer 6

ssh-keygen

creates: ~/.ssh/id_rsa ~/.ssh/id_rsa.pub

Question 7

How do ssh keys work?

Answer 7

private and public key generated by client
private key stored on client
public key copied to desired users ~/.ssh/authorized_keys
connect to server on client ssh-add ~/.ssh/id_rsa (private)

Question 8

What is the syntax to scp a file/directory to a remote machine?

Answer 8

scp /path/to/source user@machine:/path/to/destination

Question 9

What is the command to configure sshd to run automatically on boot?

Answer 9

systemctl enable sshd.service

Question 10

What is the command to configure sshd to not run automatically on boot?

Answer 10

systemctl disable sshd.service

Question 11

If using an additional unique private and public key pair, what command must you run in order to ssh into the remote machine?

Answer 11

ssh-add ~.ssh/id_rsa_second_key

• adds the clients private key to authenticate with the clients public key stored on the remote machine
• this is for additional key pairs, this is done transparently the first time a key pair is created

Question 12

What is a command to add the public key of an ssh client to the remote machine?

Answer 12

cat ~/.ssh/id_rsa.pub | ssh user@machine “mkdir -p ~/.ssh && chmod 700 ~/.ssh && cat&raquo_space; ~/.ssh/authorized_keys”

Question 13

What is the command to add the public key of an ssh client to the remote machine using ssh-copy?

Answer 13

ssh-copy-id

Question 14

What is the tmux command to create an ssh session and detach for a long running command?

Answer 14

tmux new-session -s

Question 15

What is the tmux command to rejoin a session?

Answer 15

tmux attach -t

Question 16

What is the shortcut to send commands to tmux?

Answer 16

ctrl + b
c - new window
, - rename window
d - detach session
w - list windows

Question 17

What is the tmux command to list sessions?

Answer 17

tmux list-sessions

Question 18

What is the tmux command to kill sessions?

Answer 18

tmux kill-session -t

Question 19

What us the tmux command to kill all sessions?

Answer 19

tmux kill-server

Question 20

If ssh-add fails how can you resolve this?

Answer 20

eval ssh-agent -s
or
eval “$(ssh-agent)”
Loads ssh-agent environment variables into environment

Question 21

How do you specify the private key to use if ssh is being denied?

Answer 21

ssh user@machine -i /path/to/privatekey