Category: Computers

All things computing.

Mount External, Encrypted, LMV drives

Posted on by rchapin

First decrypt the drive. When I plugged it in GNOME displayed a dialog and asked for the key. I’m guessing that cryptsetup luksOpen /dev/device device_crypt would work as well.

Run lvdisplay to get the LV Path for the logical volume that you want to mount.

Then, activate the volumes , there is a way to activate a specific one volume, but the following activates them all.

vgchange -ay

Then mount it

mount <lv-path/mnt

→ Continue reading “Mount External, Encrypted, LMV drives”

PDF Commands Cheat Sheet

Posted on by rchapin

Following are a number of common PDF processing commands on a Linux box

Convert a series of images to a PDF

convert image-1 image-2 ... images.pdf

convert-im6.q16: attempt to perform an operation not allowed by the security policy `PDF’ @ error/constitute.c/IsCoderAuthorized/426.

ImageMagick, specifically version 6 (im6), is preventing the conversion of PDF files due to a security policy. To address this

  1. As root, edit /etc/ImageMagick-6/policy.xml
  2. Search for the line <policy domain="coder" rights="none" pattern="PDF" /
  3. Update rights="none" to rights="read|write"
  4. Save
→ Continue reading “PDF Commands Cheat Sheet”

Debian Package Management Cheat Sheet

Posted on by rchapin
  • List version of an installed package: dpkg -s docker-ce | grep Version
  • Show all available versions of a package: apt-cache madison <package>

Packages being held back because of phasing

Run the following command replacing the package in question

apt-get --with-new-pkgs upgrade <package-name>

The following packages have been kept back

Try the following, in order. Each is less risky than the next. Stop as soon as you have fixed the problem.

Solution 1

apt-get --with-new-pkgs upgrade <list of packages kept back>
→ Continue reading “Debian Package Management Cheat Sheet”

How to partially cherry-pick a commit in git

Posted on by rchapin

There are times when you need to cherry-pick a commit from another branch. Then there are times when you only need parts of that commit.

Following is how you can partly cherry-pick a commit to get only the changes that you need.

Get the patch for the entire commit. Include the -n for no commit so that it does not add it as a commit to your branch

git cherry-pick -n <commit>

Then unstage the the changes from the cherry-picked → Continue reading “How to partially cherry-pick a commit in git”

Go template that properly renders delimiters for a slice of structs

Posted on by rchapin

It is common to write go text/templates that range over a slice of objects to write out a list or array of items that are separated by some delimiter defined in the template.

In the case of a JSON array of objects, the cleanest output would be a , separating each object without a leading or trailing comma.

Because go template if statements are falsey in that a 0 value will evaluate to false you can write a template as → Continue reading “Go template that properly renders delimiters for a slice of structs”

Query nested arrays in PostgreSQL JSON data

Posted on by rchapin

The following is an example showing how to query multiple nested arrays in JSON data in a PostgreSQL database.

Given

CREATE TABLE sample_json (
  id serial PRIMARY KEY,
  name varchar(64),
  json_data json
);


INSERT INTO sample_json (name, json_data)
VALUES
	(
	'NA',
	'
	{
	    "location": "US",
	    "topLevelArray": [
	        {
	            "id": 1,
	            "secondLevelArray": [
	                {
	                    "key": "someKey",
	                    "operator": "=",
	                    "value": 10
	                },
	                {
	                    "key": "foo",
	                    "operator": ">=",
	                    "value": 5
	                },
	                {
	                    "key": "someOtherKey",
	                    "operator": ">",
	                    "value": 647
	                }
	            ]
	        },
	        {
	            "id":
→ Continue reading “Query nested arrays in PostgreSQL JSON data”

How to set up a locally hosted git server and create new repositories

Posted on by rchapin

You may have code and configurations that are required to stay on premise. As a result, you will need to setup your own git server and create and manage repositories locally. Following is an overview of how to set that up.

We will leave aside server setup, configuration, and networking and assume that we have a machine on which we will host the repos, git-server, and machines that will clone, pull, and push updates, clients.

Setting up the

→ Continue reading “How to set up a locally hosted git server and create new repositories”

Setting up software RAID on Debian with mdadm

Posted on by rchapin

Software RAID has come a long way. Unless you have some very high-rate, high-volume, I/O workloads with SLAs that will otherwise cost you money, for the most part a software RAID will perform just fine. One of the primary benefits of using software RAID is the portability of your disks/data. If a box on which you have a software RAID dies somehow and at least some (depending on your RAID configuration) of drives survive, you can easily resurrect the RAID → Continue reading “Setting up software RAID on Debian with mdadm”

© 2005 Ryan Chapin