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cloud engineer

Archives for August 2021

GCP Display Device Names on OS

In GCP console you can see the VM’s Device Names. In this case, it’s boot and persistent-disk-1.

Name		          Device name
server-boot               boot	
server-data               persistent-disk-1

To display the volume names on the OS, run this command.

$ ls -l /dev/disk/by-id
total 0
lrwxrwxrwx. 1 root root  9 Aug  2 01:12 google-boot -> ../../sda
lrwxrwxrwx. 1 root root 10 Aug  2 01:12 google-boot-part1 -> ../../sda1
lrwxrwxrwx. 1 root root  9 Aug 18 18:48 google-persistent-disk-1 -> ../../sdb
lrwxrwxrwx. 1 root root  9 Aug  2 01:12 scsi-0Google_PersistentDisk_boot -> ../../sda
lrwxrwxrwx. 1 root root 10 Aug  2 01:12 scsi-0Google_PersistentDisk_boot-part1 -> ../../sda1
lrwxrwxrwx. 1 root root  9 Aug 18 18:48 scsi-0Google_PersistentDisk_persistent-disk-1 -> ../../sdb

As you can see, boot and persistent-disk-1 are displayed along with its device names /dev/sda and /dev/sdb.

Check Open Ports Remotely

Here are a few tools to check if ports are open from a remote host.

nc -zvw10 192.168.0.1 22
nmap 192.168.0.1 -p 22
telnet 192.168.0.1 22

You may have to install netcat and nmap if missing in your distro.

yum install nc
yum install nmap

Terraform GCloud VM Image Family

How to implement image family with Terraform in GCP.

Declare the machine image in terraform.tfvars.

image-family = "centos-7"

Declare data type for the machine image in maint.tf.

data "google_compute_image" "my_image" {
  family  = var.image-family
  project = "your-project-id"
}

In main.tf use “google_compute_instance” under boot disk section in main.tf.

boot_disk {
  initialize_params {
    image = data.google_compute_image.my_image.self_link
  }
}

Bash Variable Empty

Here’s how to check in Bash if a variable is empty or unset.

if [ -z "${VAR}" ]; 
then
  echo 'do something'
else
  echo 'do another'
fi

One liner

if [ -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi

The inverse

if [ ! -z "${VAR}" ]; 
then
  echo 'do something'
else
  echo 'do another'
fi
if [ ! -z "${VAR}" ]; then echo 'do something'; else echo 'do another'; fi

Markdown Language

Style your text using markdown. If you use GitHub, markdown will come in handy.

Examples:

# This is an <h1> tag
## This is an <h2> tag
###### This is an <h6> tag

Here are more markdown examples.

Corosync Settings

Here are the SAP Corosync settings.

[root@server ~]corosync-cmapctl | grep fail_recv_const
runtime.config.totem.fail_recv_const (u32) = 500

Sublime Text Terraform Syntax

If you use Terraform and Sublime Text, add Terraform Syntax Highlighter using Package Control.

Press Ctrl+Shift+P or Cmd+Shift+P.
Select “Package Control: Install package”
Select “Terraform”

It should install in a few seconds.