Tag: ssh

Tmux Cheat Sheet & Quick Reference

Start a new session

tmux
tmux new
tmux new-session

Start a new session with the name mysession

tmux new -s mysession

kill/delete session mysession

tmux kill-session -t mysession

kill/delete all sessions but the current

tmux kill-session -a

kill/delete all sessions but mysession

tmux kill-session -a -t mysession

Show all sessions

tmux ls
tmux list-sessions

Attach to a session with the name mysession

tmux a -t mysession
tmux at -t mysession
tmux attach -t mysession
tmux attach-session -t mysession

Rename session

Ctrl + b $

Detach from session

Ctrl + b d

Create window

Ctrl + b c

Rename current window

Ctrl + b ,

Close current window

Ctrl + b &

Previous window

Ctrl + b p

Next window

Ctrl + b n

Switch/select window by number

Ctrl + b 0 ... 9

Scroll

Ctrl-b [
# Press q to quit scroll mode
Ctrl-b PgUp

References
https://tmuxcheatsheet.com/
https://gist.github.com/MohamedAlaa/2961058

Keep Alive SSH Sessions

To keep an SSH connection alive, you can modify your SSH configuration to send periodic keepalive messages. Here are a few methods to achieve this:

Method 1: Modify the SSH Client Configuration

  1. Edit the SSH client configuration file (/etc/ssh/ssh_config or ~/.ssh/config): 
    nano ~/.ssh/config
  2. Add the following lines to send keepalive messages every 60 seconds: 
    Host *
    ServerAliveInterval 60
    ServerAliveCountMax 3
    • ServerAliveInterval specifies the interval in seconds between keepalive messages.
    • ServerAliveCountMax specifies the number of keepalive messages that can be sent without receiving a response from the server before the connection is terminated.

Method 2: Modify the SSH Server Configuration

  1. Edit the SSH server configuration file (/etc/ssh/sshd_config): 
    sudo nano /etc/ssh/sshd_config
  2. Add or modify the following lines to keep the server alive: 
    ClientAliveInterval 60
ClientAliveCountMax 3
    • ClientAliveInterval specifies the interval in seconds that the server will wait before sending a null packet to the client to keep the connection alive.
    • ClientAliveCountMax specifies the number of client alive messages which may be sent without receiving any messages back from the client.
  3. Restart the SSH service to apply the changes: 
    sudo systemctl restart sshd

     

Set Up SSH Keys on Ubuntu

Create the RSA Key Pair

ssh-keygen -t rsa -b 4096 -C "[email protected]"

Copy the Public Key to Ubuntu Server

cat ~/.ssh/id_rsa.pub | ssh username@remote_host "mkdir -p ~/.ssh && touch ~/.ssh/authorized_keys && chmod -R go= ~/.ssh && cat >> ~/.ssh/authorized_keys"

or Copying Public Key Manually

To display the content of your id_rsa.pub key, type this into your local computer:

cat ~/.ssh/id_rsa.pub

You will see the key’s content, which should look something like this:

ssh-rsa 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 demo@test

make sure the ~/.ssh directory exists.This command will create the directory if necessary, or do nothing if it already exists:

mkdir -p ~/.ssh

Now, you can create or modify the authorized_keys file within this directory. You can add the contents of your id_rsa.pub file to the end of the authorized_keys file, creating it if necessary, using this command:

echo public_key_string >> ~/.ssh/authorized_keys

Finally, we’ll ensure that the ~/.ssh directory and authorized_keys file have the appropriate permissions set:

chmod -R go= ~/.ssh

or Copy using ssh-copy-id

ssh-copy-id [email protected]
ssh-copy-id [email protected] -p 22000
ssh-copy-id -i id_rsa.pub -p 22000 "[email protected]"

use -i identity_file for other identities

Authenticate to Ubuntu Server Using SSH Keys

ssh username@remote_host

Disable Password Authentication on your Server

sudo nano /etc/ssh/sshd_config
PasswordAuthentication no
sudo systemctl restart ssh

Convert private key to putty 

puttygen keyname -o keyname.ppk

ssh “permissions are too open” error

Keys need to be only readable by you:

chmod 400 ~/.ssh/id_rsa

If Keys need to be read-writable by you:

chmod 600 ~/.ssh/id_rsa

References
https://www.digitalocean.com/community/tutorials/how-to-set-up-ssh-keys-on-ubuntu-1604
https://haydenjames.io/how-to-convert-openssh-keys-to-putty-ppk-on-linux-with-puttygen/
https://help.github.com/en/articles/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent
https://stackoverflow.com/questions/9270734/ssh-permissions-are-too-open-error