bash-scripting

NOTE: The repository structured for the scriptbox VM. All the bash scripts were/can be placed in /opt/scripts directory into the scriptbox VM

See Vagranfile for more information on the below VM configurations

scriptbox: CENTOS VM (main VM, from where we are running all the scripts and connecting to other VMs using ssh connection)

web01: CENTOS VM

web02: CENTOS VM

web03: UBUNTU VM

General Notes:

• Make sure to make the script executable (chmod +x <file-name>.sh) to be able to execute the script from the shell.
• ./<filname>.sh to execute the script.
• nohup <command> to execute the command in the background.
• <command> > /dev/null to generate no output.
• Once we connect to a VM using SSH for the first time, it asks for permission to store a fingerprint - SHA256:<fingerprint>, that file is ~/.ssh/known_hosts.
• To remove all the known hosts (means it will ask for the permission to store the fingerprint once you try to SSH into the machine again) use - cat /dev/null > ~/.ssh/known_hosts

Generating SSH Keys

• ssh-keygen: It will generate two keys -- One is the Public Key (stored at /root/.ssh/id_rsa.pub) and other is the Private Key (stored at /root/.ssh/id_rsa). Public Key acts as a lock and Private Key as the key to establish the connection.

• ssh-copy-id devops@web01: General -> ssh-copy-id <user>@<hostname> this will apply the ssh login authentication instead of the password based authentication on the user devops and host web01.

• vim /etc/ssh/sshd_config: Update this file in UBUNTU to enable password based authentication first. Then only we can apply the key based authentication using the scriptbox VM.

• The below command can be used to execute commands remotely from the scriptbox VM on web01, web02, web03. (Make sure the local host entry has been made with <IP> <HOSTNAME>, for example 192.168.10.52 web01)

  • $ for host in `cat remote_hosts`; do ssh devops@$host uptime; done