How To Start A Script To Complete Configuration

Home » CentOS » How To Start A Script To Complete Configuration
CentOS 9 Comments

Hi,

We have a virtual environment based on XenServer. In this environment I
defined a template for CentOS 7 servers.

I would like to start a script a boot time to complete the configuration of new VMs based on this template. How can I have a script started before any login prompt to ask question to the user to complete the configuration such as hostname, IP address, etc?

Thanks, Bernard

9 thoughts on - How To Start A Script To Complete Configuration

  • Hi Bernard,

    My first impulse was “don’t!”, and that’s probably the best advise. A popular model is that the “firstboot” package takes care of this at the first user login, and *nix systems sort of depend on this “logged in users do stuff” model.

    Even better, use ansible, cfengine, chef, or puppet to automate the task of setting things up. This is the _best_ solution and you will eventually come back to it.

    But, the darker, cynical part of my brain, the part that says
    “what, you’re cutting down on coffee?” part, said “sure you can”. Here’s how it _could_ be done.

    DON’T DO THIS. TURN BACK NOW.

    Replace /sbin/init with a shell script that does what you want.
    It will be the first userland process started, have the console
    for I/O, and run as root. At completion, restore the original
    /sbin/init and reboot. Leave no traces behind. Do not document
    your awful hack, others will use your words against you.

    Best regards,

  • IIRC, there’s a BootP module for Ansible. I’m not at a place where I can verify that though.

    —

    Mark Haney ::: Senior Systems Engineer
    *VIF* *International Education*
    P.O. Box 3566 ::: Chapel Hill, N.C. 27515 ::: USA
    919-265-5006 office

    Global learning for all. http://www.viflearn.com Find VIF on Facebook <http://facebook.com/VIFInternationalEducation> |
    Twitter <https://twitter.com/vifglobaled> | LinkedIn
    <http://www.linkedin.com/company/vif-international-education>

    Recognized as a ‘Best for the World’
    <http://bestfortheworld.bcorporation.net/> B Corp!

  • Hello, I think you can use anaconda for this task, you can configure some actions after the installation.

    Best regards,

    El dt, 8 nov 2016 a les 18:44 Leon Fauster va escriure:

  • How you could do this with scripts:

    *CentOS 7*

    1. Deploy a VM from your base CentOS 7 template
    2. Copy your “my-firstboot.sh” script (or whatever its called) to a
    location such as /root/scripts/
    1. This scripts only job should be to mount a NFS location and
    execute any post install scripts you have stored there, and provide a log
    file.
    2. This script should disable the “my-firstboot.service” at the end
    and then change permissions of itself to no execute to ensure it doesn’t
    get run more than once.
    3. It is also useful to have this script email the system admins when
    its done and reboot the VM (in the case of full system updates that require
    a reboot to new kernel)
    3. Create your “my-firstboot.service” unit file at: /etc/systemd/
    system/my-firstboot.service, enable it. example contents:
    1. [Unit]
    Description=Auto-execute my post install scripts
    After=network.target

    [Service]
    ExecStart=/root/scripts/my-firstboot.sh

    [Install]
    WantedBy=multi-user.target

    *CentOS 6*

    1. Same thing as above, except no service unit file. Instead simply
    create a line in /etc/rc.local to execute the “my-firstboot.sh” script like
    so:
    1.

    echo “/root/scripts/my-firstboot.sh” >> /etc/rc.d/rc.local

    2. And have the “my-firstboot.sh” script remove that same line above
    from rc.local at the end of its execution so its not run again on the next
    reboot.

    Bill

  • Forgot to mention. After this is setup, shutdown the VM and create a template from it. Then, any VMs created from this new template will auto execute your scripts.

    Bill

  • If you’re just talking about VMs and templates, you can try
    ‘virt-builder’ or ‘virt-sysprep’ for manipulating the templates directly (Instead of booting them up in a full VM).

    Theses tools also allow you to inject scripts and commands to be run once a VM created from the template is brought up for the 1st time.

    Another option to consider is installing the cloud-init package in the VM. Some virtual environments allow you to inject instructions into VMs using cloud-init.

  • To Bill,

    The script solution is what I try to do. I am close to it. The problem I
    am facing at the moment is that this script need to be interactive to have input from the sysadmin.

    I tried to add the following lines to the service unit file to direct the interaction of the script to tty1 but without success:
    StandardInput=tty TTYPath=/dev/tty1
    TTYReset=yes TTYVHangup=yes