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VirtualBox create host-only interface and attach

A host-only network interface is one created in software which appears on the host system.

This interface can then be attached to one or more VMs - allowing for connectivity between those VMs and free communication between the host system and connected VMs.

• Create & attach interface
• Configure Ubuntu guests
  • Ubuntu 18.04+
  • Ubuntu pre 18.04
• Reference

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Git correct a commit via --fixup

Initial commit state:

$ git log --oneline
733e2ff Second widget done
fb2f677 First widget done
ac5db87 First commit

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Modify DNS for Optus supplied Huawei B315 4G modem

The Huawei B315 modem supplied by Optus for the (now defunt) Vividwireless service is a workable but sadly rather crippled device, even down to the inabiilty to modify assigned DNS servers from it's DHCP server away from Optus DNS to something sane (Google DNS/Cloudflare/etc.).

This script should allow for the easy update of assigned DNS servers and has been tested with Google Chrome.

Usage

• Log into router web UI (e.g. http://192.168.0.1).
• From the same browser session, open the "web developer tools" pane.
• Drop the contents of dnsmodify.js into Console area - modifying ROUTER_URI, PRIMARY_DNS and SECONDARY_DNS to suit.
• Run the script, updated DHCP settings are pushed and modem will restart.

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GitHub pull request toggle "force-pushed" events bookmarklet

Since November 2018, GitHub have started to display forced push events to pull request page timelines. This bookmarklet will toggle display of these events if they are getting in the way of meaningful commits.

Add the code below as the URL of a new bookmark:

javascript:((d)=>{if(d.getElementById('nuke-fp')==null){let e=d.createElement('style');e.id='nuke-fp';e.innerHTML='.nuke-fp{display:none}';d.getElementsByTagName('head')[0].appendChild(e)}for(let e of Array.from(d.querySelectorAll('.discussion-timeline .discussion-item-head_ref_force_pushed'))){e.classList.toggle('nuke-fp')}})(document)

Tested with Chrome 70.0.3538.102.

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'use strict';

async function* delayList() {

	function delay(timeout) {

		return new Promise((resolve,reject) => {

			setTimeout(() => resolve(`dealyed for: ${timeout}ms`),timeout);
		});

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CIDR fit

Python function to determine if a given IPv4 CIDR fits into another.

How cidr_fit(cidr_a,cidr_b) works:

• For both CIDR's given:
  • Splits each CIDR in address and prefix size parts.
  • Converts the address part to a 32 bit binary string.
    • E.g. 192.168.0.1 becomes 11000000101010000000000000000001.
  • Cuts out everything after the prefix size.
    • E.g. 192.168.0.1/12 becomes 110000001010.

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Gmail retention/purge by label Google script

A Google Apps Script which adds pseudo message retention-like policies against specific labels for a Gmail account.

• How it works
• Install
• Reference

How it works

• Apps Script function is called automatically on a regular schedule.
• Script iterates over a set of predefined message labels.

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Add user ssh-agent as daemon to Ubuntu 18.04LTS server

Create a new systemd user unit, which starts ssh-agent upon login to server. Will remain resident until the final session for the user has logged out.

Steps

• Create /etc/systemd/user/ssh-agent.service.

• Run the following commands (under your user account, not root) to install the systemd unit and start:

   $ systemctl --user enable ssh-agent.service
   $ systemctl --user start ssh-agent.service

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Bash shift quirks

When using the shift built-in, have noted this interesting behavior which I have been unable to find documentation for.

Update: the answer was right in front of me, if shift is called with a value greater than arguments available in $1 - $x then it will return with a non zero status - hence the script will halt (since I'm using set -e)!

Using the script test.sh, executed using arguments:

./test.sh apple orange banana
apple

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CloudFormation example for API Gateway integration to Lambda function

Template that will create the following:

• API Gateway endpoint:
  • A single root method, accepting POST requests only with Lambda proxy integration to a function.
• In-line Lambda function echoing back requesting users IP address to API Gateway requests:
  • IAM role for Lambda allowing CloudWatch logs access.
  • Permissions for Lambda that allow API Gateway endpoint to successfully invoke function.
• CloudWatch logs group for Lambda, with 90 day log retention.

After standing up the template, you should be able to curl a POST request to the URL listed as the apiGatewayInvokeURL output value.