Linux Server tips

passwords and sudo

• passwordless sudo: sudo visudo
• change password: sudo passwd <user>

SSH keys configuration

configuring on client machine

• generate a new SSH key pair:
  • ssh-keygen -t ed25519 -C "<device-name>"
  • ed25519: private key → stays on this device only
  • ed25519.pub: public key → safe to share with servers and GitHub

• store generated key on github (optional, works as auth for github and allows you to easily deploy to new servers)
  • store: gh ssh-key add ~/.ssh/id_ed25519.pub -t "<device-name>"
  • verify: gh ssh-key list

• add generated key to ssh agent (optional, allows you to use the key without specifying it every time)
  • macOS/Linux: ssh-add ~/.ssh/id_ed25519
    • if agent is not running, start it: eval "$(ssh-agent -s)"
  • Windows: ssh-add $env:USERPROFILE\.ssh\id_ed25519

• config on client (optional)

  • macOS/Linux

    Host <host1> <host2>
        User <username>
        IdentityFile ~/.ssh/<identity_file>
        AddKeysToAgent yes
        UseKeychain yes
    Host <host1> <host2>
        IdentitiesOnly yes
        ServerAliveInterval 60
        ServerAliveCountMax 3
    
    Host <host3>
        HostName <host1.url>
        User <username>
        IdentityFile ~/.ssh/id_ed25519
    

  • Windows
    • add key: ssh-add $env:USERPROFILE\.ssh\id_ed25519
    • verify:ssh-add -l
  • troubleshooting
    • verbose: ssh -v user@hostname
    • use specified key: ssh -i %USERPROFILE%\.ssh\id_ed25519 user@hostname

configuring on servers

• Windows: copy public key to .ssh/authorized_keys on server

• Linux/macOS:

  mkdir -p ~/.ssh
  chmod 700 ~/.ssh # only user can read/write/execute
  ssh-copy-id -i <key> <user>@<server>
  chmod 600 ~/.ssh/authorized_keys # only user can read/write, no execute
  

• Distribute from GitHub

  • gh ssh-key list to get key ids
  • GitHub exposes your public keys at: https://github.com/<username>.keys
  • Deploy to a server in one line: curl https://github.com/<username>.keys >> ~/.ssh/authorized_keys

using SSH keys for GitHub

• add SSH key to GitHub account (optional, allows you to use SSH for Git operations instead of HTTPS)
  • gh ssh-key add ~/.ssh/id_ed25519.pub -t "<device-name>"
  • verify: gh ssh-key list
• test SSH connection to GitHub: ssh -T git@github.com