Category: system admin

Postgres DB migration error due to replication

November 26, 2021 / abhijit

We got a weird error today when running the latest migration on a production Postgres DB.

cannot update table "schema_info" because it does not have a replica identity and publishes updates

The table schema_info is created when we run ruby Sequel migrations. This table stores just the version number of the latest migration applied under a column called version.

We had set up a replica database some time ago and it looked like the issue was because of this.

Disable specific default Windows key shortcuts

November 15, 2021 / abhijit

A number of times, I prefer to use the Windows key on the keyboard to create shortcuts, especially to applications which I use frequently.

However, Windows has a default set of keyboard shortcuts that it maps to various applications and those key mappings can’t be changed. A few examples are Cortana (Win+C), Clipboard (Win+V).

To get around this, the Registry Editor needs to be modified.

users and sudo in Linux

November 1, 2021 / abhijit

Every time I need to create, modify, grant sudo access to users in Linux, I have to search for it.

This is a list of the commands I’ve used in the past.

Will keep updating this so that I don’t have to load a search page every time!

All commands below are run as root user. If I’m not the root user, I need to prefix them with sudo!

Create Postgres replica on separate server over the network

October 30, 2021 / abhijit

A database replica is able to provide another layer of protection in case of the main database server going down.

Postgres has this capability out of the box.

In this case the requirement was to create a replica on a separate server. (It’s also possible to create it on the same server where Postgres is running).

The replica maintains an exact copy of the main database (called Primary) on a real-time basis.

Run Postgres exposed to the internet

October 30, 2021 / abhijit

Although this is not recommended, there might be scenarios where there are no other options.

An example is an analysis software which doesn’t give the capability to connect via SSH. I came across this scenario when someone wanted to use QLik. Although this has a lot of capabilities, but when something like this is required, I’d rather use the open source and free Metabase.

Compile fossil on Ubuntu Linux

September 25, 2021 / abhijit

Recently, I had to build fossil from source on Ubuntu because I needed to make a change to the source code.

It required a number of dependencies which is expected to be installed.

They are –
gcc (obviously!)
zlib1g and zlib1g-dev
tcl-dev
tk
libssl
libssl-dev

Setup up READ_ONLY users on Postgres

August 28, 2021 / abhijit

To grant access to users for only viewing a database (i.e. no INESRTs or CREATE or UPDATE access) there are certain conditions.

First, access should be only allowed through ssh.

Second, the ssh user should not be able to get into a shell directly.

And finally, the database should restrict access to that particular user with relevant permissions.

PM2 – the best process manager

June 22, 2021 / abhijit

In the past, on my server I’ve installed Fossil, Syncthing, Bitwarden, Inlets. All these require some form of Process Management. These programs / processes / services need to be always running, so they are restarted in case they get terminated. Also, on a system restart these need to start up automatically.

I’ve mostly used Systemd or Supervisor to all these things.

However, I recently came across PM2 and I was really blown out of my mind as to how simple it was to set it up.

moving from LastPass to bitwarden using vaultwarden (bitwarden_rs)

May 1, 2021 / abhijit

I have been using LastPass for password management since like forever.

I became a paid customer in 2014. It was initially $1/month. Then it got hiked to $2/month and currently it stands at $3/month. That’s $36/year which was working out too much for me.

Furthermore, the free option is limited to a single type of device. Since I wanted to use it across desktops and mobiles, there was no option except for the $3/month plan.

I had been looking at bitwarden for quite some time now but read that it’s too resource heavy. I then came to know of biwarden_rs which is a rewrite of bitwarden in Rust and compatible with upstream Bitwarden clients. I had then forgotten about this for some time until I head the news of it being renamed to vaultwarden via a Reddit thread.

nginx: [emerg] SSL_CTX_use_PrivateKey_file failed for GoDaddy SSL

April 14, 2021 / abhijit

I got this weird error while deploying an SSL certificate from GoDaddy

nginx: [emerg] SSL_CTX_use_PrivateKey_file failed (SSL: error:0909006C:PEM routines:get_name:no start line:Expecting: ANY PRIVATE KEY error:140B0009:SSL routines:SSL_CTX_use_PrivateKey_file:PEM lib)