https://indico.cern.ch/event/817056/contributions/3417073/attachments/1837344/3010849/190502_System_Test_Meeting_-_nanoCrate.pdf

https://indico.cern.ch/event/842824/attachments/1920624/3177632/PreparingFC7.pdf

• More information: 2019 Phase 2 DAQ school: https://indico.cern.ch/event/842824/

Note: at the time of writing, it does not seem to be possible to install CERN's CentOS7 (CC7) OS from an external drive (e.g. USB stick), because the ISO image in the official repository does not contain a boot partition. Due to this, these instructions apply to the standard CentOS7 OS.

The main steps to install CentOS7 from an external USB drive are summarized below.

• Write the CentOS7 boot image to a USB disk.
  
  
  1. Find a working USB disk (if unsure, try to write a standard Ubuntu image on it, and verify if the USB disk boots correctly).
     
     
  2. Connect the USB disk to a laptop with Internet access.
     
     
  3. Find the name of the device corresponding to the USB disk; in the following, this is assumed to be /dev/sda.
     
     
  4. Download the CentOS7 boot image at
     http://mirror.centos.org/altarch/7.8.2003/os/i386/images/boot.iso (for 32-bit OSs)
     http://mirror.centos.org/centos-7/7/os/x86_64/images/boot.iso (for 64-bit OSs)
     In the following, the path to this file on your local machine is assumed to be boot.iso.
     
     
  5. Write the image to the USB disk with the following command
     sudo /bin/dd if=boot.iso of=/dev/sda bs=4M status=progress oflag=sync

• Connect the USB disk to the computer on which CentOS7 should be installed, and restart the system booting from the USB disk.

• If the USB disk is not booted by default before the computer hard-drive, access the computer's boot settings at startup (usually, this can be done by pressing F12, or F9, before the boot sequence starts).

• Follow the installation instructions.
  
  
  1. Configure the system as required (timezone, keyboard layout, etc).
     
     
  2. If necessary, enable explicitly the LAN, or WiFi, connection.
     
     
  3. Under “Installation Source”, input the http address (it is not necessary to write explicitly http:\/\/):
     [32-bit] mirror.centos.org/altarch/7.8.2003/os/i386
     [64-bit] mirror.centos.org/centos-7/7/os/x86_64
     and do not tick the box stating “This URL refers to a mirror list”.
     
     
  4. Select the software packages to be included in the installation (example: “GNOME Desktop”, “GNOME Applications”, “Compatibility Libraries”, and “System Administration Tools”).
     
     
  5. If necessary, in “Installation Selection”, select the target hard disk and reclaim the necessary disk space (requires selecting the hard disk, clicking on “Delete All”, and then “Reclaim Space”).
     
     
  6. Start the installation.
     
     
  7. Input the root password, and configure user accounts; tick the box “Make this user administrator” to give sudo rights to a given user (the user is added to the wheel group).
     
     
  8. Wait for the installation to finish, then reboot, as per instructions.
     
     
  9. After rebooting, complete the installation procedure (authentication, and change of host name), then log in.
     
     
  10. Manually install any additional packages that may be needed, for example
      sudo yum -y install git emacs

Optional: to apply CERN's updates on top of the standard CentOS7 OS, the script linked here can be used (last tested on Aug. 6, 2020; written by Lars Noethe). The only prerequisite to run it is the .repo file for the relevant CC7 packages to be added (this file can be obtained from the CERN Service Desk).