Posts on Costin Stefan

I joined 512kb.club

Sun, 15 Feb 2026 00:00:00 +0000

My website is now part of 512kb.club - a curated list of sites whose total size is under 512KB. That’s it. Half a megabyte. Even less, actually, because my blog was reported at 410K.

In 2026, when even basic websites are rebuilt as React applications, that almost feels rebellious.

BGP core memory

Tue, 18 Nov 2025 00:00:00 +0000

So recently I had to play with BGP after a very long time. I have a router that connects to external via an eBGP session. It gets default route from there and it advertises the originating prefixes. All worked great until I wanted to advertise a new /24 subnet.

How to improve Wordpress performance

Sat, 21 Jun 2025 00:00:00 +0000

In this one I will show you how I improved the performance of a WordPress site using CloudFlare Caching and PHP FPM pool settings.

But a bit of context. I have 2 WP websites running on the same VPS behind nginx, with 2 different conf file. Pretty standard deployment so far. On this VPS I have root access, so I’m able to play a bit more with other stuff, not just standard cPanel settings.

How to empty a file in Microsoft Windows without deleting it

Wed, 14 May 2025 00:00:00 +0000

As part of my freelancing business, I recently had to fix a space issue on a Windows machine. And the issue was caused by a very large text file.

I know the Linux way of emptying a file, which is to redirect STDIN to the file.

RedHat Openshift, container IDs and cgroups

Thu, 08 May 2025 00:00:00 +0000

So I had a really interesting issue recently where one of our app devs was complaining that he can’t get the container ID from within the container in a new environment.

For context, there’s a setup with 3 identical environments on the customer side and a local lab that was recently replaced. I’ve deployed a new Openshift cluster (version 4.14. will become important later) to replace another lab environment in a different location.

Microsoft announced Think Deeper, free access to GPT o1 model

Fri, 31 Jan 2025 00:00:00 +0000

So recently Microsoft announced they’re offering ChatGPT o1 model free to their Copilot program. So I’ve decided to give it a go and see how it goes.

First I’ve connected to https://copilot.microsoft.com with both a personal account and a work account.

I’ve tested the announcement of this by asking it directly:

How to analyze and fix a pod scheduling issue due to Insufficient Memory on Kubernetes or Openshift.

Thu, 09 Jan 2025 00:00:00 +0000

So it may happen that you have a Kubernetes or Openshift deployment and a pod does not want to start and remains in Pending state.

First, let’s check the events that are causing this:

[root@server ~]# k get events -n <namespace>
LAST SEEN   TYPE      REASON             OBJECT            MESSAGE
31m         Warning   FailedScheduling   <namespace>/<pod_name>   0/13 nodes are available: 10 Insufficient memory, 3 node(s) had taint {node-role.kubernetes.io/master: }, that the pod didn't tolerate, 4 Insufficient cpu.

As we can see, the reason is FailedScheduling and the message complains about insufficient memory and insufficient cpu.

How to get audio notification from CLI when server or service is reachable

Tue, 31 Dec 2024 00:00:00 +0000

If you’re working on fixing an issue on a server and want to be notified as soon as this is reachable, you can run an audio alert. Below I have a list of variations of the Bell Character.

Windows / PowerShell:

 while ($true) {if (Test-Connection -quiet 1.1.1.1) { [console]::beep() }}

Windows / cmd:

for /L %n in () do @ping -n 1 1.1.1.1 && echo ^G

WSL2 / Bash:

while true; do sudo ping -q 1.1.1.1 -w1 >/dev/null && tput bel; sleep 5; done

on WSL ping needs eleventation so sudo is mandatory.

How to configure Roundcubemail for iCloud custom domain email address

Fri, 25 Oct 2024 00:00:00 +0000

So I’ve tried to configure a self-hosted Roundcube container and set up an iCloud account with a custom domain address.

Something like what this guy wanted to do a couple of years ago. Unfortunately, there was no tutorial available on the internet, so here I am creating one for you :)

How to automate testing webapps

Tue, 04 Jun 2024 00:00:00 +0000

For today’s post I will walk you through the process of setting up a web-app testing environment automatically using ansible.

I will split this into 2 parts. First part will focus on creating the automation needed to deploy the containers on proxmox. Second part is about creating the tester tool solution.

How to get display monitor serial number from PowerShell

Wed, 24 Apr 2024 00:00:00 +0000

This is a quick one, I had to get the SN of my external screens recently and I thought I should share the powershell command I used for this task. This works only on your local machine, for AD nodes there are other options out there on the internet.

PostgreSQL performance test script

Wed, 24 Apr 2024 00:00:00 +0000

In case you want to run a quick performance test (in simple terms of access to DB) on a PostgreSQL server, this can be done quickly through a python module called psycopg2.

This is the python script I’ve used:

 1#!/usr/bin/python3
 2import psycopg2
 3from psycopg2 import Error
 4import time
 5
 6def create_connection():
 7    """ create a database connection to a PostgreSQL database """
 8    try:
 9        conn = psycopg2.connect(
10            database="postgres",
11            user="postgres",
12            password="postgres",
13            host="1.2.3.4",
14            port="5432"
15        )
16        print('Successfully Connected to PostgreSQL')
17        return conn
18    except Error as e:
19        print(e)
20
21def check_table_exists(conn):
22    """ check if a table exists in the PostgreSQL database """
23    cur = conn.cursor()
24    cur.execute(f"SELECT 1;")
25
26def main():
27#    table_name = 'pg_auth_members'
28
29    # create a database connection
30    conn = create_connection()
31
32    # check if table exists
33    with conn:
34        start_time = time.time()
35        checks = 0
36        while True:
37            check_table_exists(conn)
38            checks += 1
39            elapsed_time = time.time() - start_time
40            if elapsed_time > 0:
41                tps = checks / elapsed_time
42                print(f'Current TPS: {tps}')
43                print (f'Current checks: {checks}')
44
45if __name__ == '__main__':
46    main()

In here you should update the database, user, password, host and port to something relevant to your environment. Everything else can stay the same.

How to fix "Could not connect to one or more vCenter Server"

Thu, 28 Sep 2023 00:00:00 +0000

Recently I had to fix a vCenter Server that was stopped working. The webpage displayed the following error, and the automated backup jobs stopped working.

Could not connect to one or more vCenter Server systems: https://$VCENTER_FQDN:443/sdk

The version is rather old and end of life (6.7), so VMware support was out of the question. Which means I had to do it all by myself. Great…

How to move artefacts in a Jfrog repository

Thu, 28 Sep 2023 00:00:00 +0000

This one will be a quick one. Recently I had to move several hundred artefacts from a Jfrog repo folder up one level. Easy peasy, right? But the problem was that manual work from GUI would take forever and my work time is limited so I had to find a different way.

How to automate your blog posts

Fri, 17 Feb 2023 00:00:00 +0000

Since I’ve transformed this website in a Blogging as a Service (BaaS) thing with the help of Github Actions and Github Pages my life was much easier.

Let me help you do the same.

First thing you’ll need is a domain. For this domain you will need a NS, and for this you can use CloudFlare for free. They offer a great service, btw.

How to restore a Kubernetes cluster after IP change

Wed, 18 Jan 2023 00:00:00 +0000

Recently I had to fix a kubernetes cluster which had its IP addresses changed. The team that changed the IP address on the machines also replaced the hostname in /etc/hosts. However, this is not enough. In order to restore the cluster, you also have to change the IP address in kubernetes cluster manifest files.

New year, new changes

Sat, 14 Jan 2023 00:00:00 +0000

After a period on which I focused more on work, I’ve decided I need to change a bit the blog. 9 months ago I’ve migrated my blog from DigitalOcean to Github Pages. DigitalOcean was great for me when I started my first droplet, but I wanted to experiment with other technologies. So I’ve migrated my blog to Github Pages and my email to Apple Mail.

How to change NTP server on HP 3PAR 7200c

Sat, 19 Sep 2020 00:00:00 +0000

Recently I had to add more NTP servers to a HP 3PAR 7200c storage. Here’s how I did it:

3PAR_hostname cli% setnet ntp -add 10.90.221.13
NTP server successfully updated.

Show current NTP server(s):

3PAR_hostname cli% shownet
IP Address  Netmask/PrefixLen Nodes Active Speed Duplex AutoNeg Status
10.23.155.8   255.255.255.192    01      1  1000 Full   Yes     Active

Default route :                                     10.23.155.1
NTP server    :   {} 10.102.102.132 10.102.102.133 10.90.221.13
DNS server    :                                            None

Remove one NTP server:

How to bypass Chrome error "Your connection is not private"

Tue, 30 Jun 2020 00:00:00 +0000

If you’re an IT professional that has to deal with old systems that have self-signed certificates you most probably had to add exceptions to your browser many times. Maybe even import those self-signed certificates locally.

Unfortunately when you’re working on a customer’s jump host this is not an option. And starting with more recent version of Chrome this is not possible anymore, you don’t have the option to Add it as an exception.

How to quickly enable a low-resource webserver

Wed, 29 Apr 2020 00:00:00 +0000

Have you ever wanted to just start a Webserver in a second, for a quick and dirty task but didn’t want to install a full LAMP/LEMP stack? This is possible with the help of a python module and here it is in action:

How to create a SSL profile when you don't know the key passphrase

Mon, 24 Feb 2020 00:00:00 +0000

On F5 BigIP LTM you can create a SSL profile even if you don’t know the private key passphrase

This workaround can be applied only if you’ve used the private key on the same F5 BigIP node already. In my case, I had to reuse the same cert+key from a server-ssl profile on a client-ssl profile. And because business was in a hurry and they didn’t have the private key anymore, I had to find alternative ways of making it work.

How to fix do-agent exited with a return code 100

Sun, 16 Feb 2020 00:00:00 +0000

So recently I’ve encountered the error in the subject. This came after 2 major changes (OS upgrade and PHP upgrade). So definitely it had to do with one of them. My money were on the first one. I’ve looked around on the internet and the only thing I could see was this old article that had no solution: https://www.digitalocean.com/community/questions/do-agent-exited-with-a-return-code-100

How to CTRL+ALT+DEL in RDP

Tue, 22 May 2018 00:00:00 +0000

ctrl+alt+end

How to fix Microsoft Lync/Outlook has stopped working

Tue, 15 May 2018 00:00:00 +0000

Recently I had this issue that ate a big part of my day. Here’s how I fixed it.

Firstly, some background info

I’m using a Win 10 (Version 10.0.14393) OS with Office 2013 [15.0.4569.1503]. The previous day I’ve been prompted to restart my laptop to complete the new updates. I’ve left in a hurry and just closed the lid. The laptop didn’t close and I had to use the power button to stop it. I knew I was in trouble at this point, but had to attend a meeting and didn’t have time to wait for the updates.

Networking training materials

Mon, 11 Dec 2017 00:00:00 +0000

I’ve stumbled upon this great list of materials you can use to get started on IT, and Networking in particular. I have to admit that some are new for me, even after being in this field for over 12 years.

Udemy offline

Tue, 05 Dec 2017 00:00:00 +0000

Here’s another cool and helpful thing I just discovered that might help you stranger of the internet.

Recently I joined a class on Udemy.com, and because I have other tasks at the moment and can’t dedicate 100% to it, I wanted to download the videos so I started looking for ways how to do it. The official answer is that they don’t have anything against it, but it depends on the instructors. In my case the option to download the video was not present, plus that I wanted to automate the process and not download the videos one by one.

Quagga

Fri, 01 Dec 2017 00:00:00 +0000

After having some interviews where I’ve been asked about routing on linux solutions, I’ve decided to playaround with Quagga. As always, you can find all the info already on the internet. And in my case Brian Kletter had all the necessary info to setup the environment. Here’s the link on how to setup a linux server with quagga software. And here the initial setup for quagga.

How to create text files on Cisco routers

Mon, 07 Aug 2017 00:00:00 +0000

In case you will need it, here’s a thing that helped me out once. In case you want to append some config lines that you have stored in a file and if you can’t copy it through SFTP, you can make it locally. To do this you need to start tclsh and create the file puts [open "flash:filename" w+] { now don’t press enter but just paste in your config lines and then } and ENTER. tclquit to exit tclsh. Now you’ll have your config snippet in flash:filename and you can use it to append to your config. Would be a good idea to check it with more flash:filename just to be sure that you have everything in place and no characters were left outside. As always, more info on Cisco’s webpage

Password recovery procedure on Cisco Catalyst 3500-XL

Mon, 07 Aug 2017 00:00:00 +0000

Just got a used Catalyst 3500-XL switch and don’t have credentials? Did you forget your auth credentials or you just want to have fun?

Accessing a Cisco switch when you don’t have the right credentials is hard but not impossible.

If you have issues connecting the console cable, try to install the drivers first.

Cisco guest shell

Fri, 07 Jul 2017 00:00:00 +0000

So, it seems that finally Cisco decided to introduce a shell for their routers. I know this already exists for their FirePower plaform, but from my knowledge, they just made it available for routers.

Enabling the shell

To enable the feature we simply have to enable iox and then we can enter linux land with guestshell

Life tip

Wed, 31 May 2017 00:00:00 +0000

I’ve recently stumbled upon a great course on coursera which can teach you how to learn in today’s world. With all the distractions that interrupts us everyday. I wish I’d find it sooner.

How to configure Cisco devices remotely

Thu, 04 May 2017 00:00:00 +0000

So, let’s assume you are a network engineer that has to configure something on a new Cisco switch/router. You don’t have console access and just connect to the box via ssh. You either have a typo in your commands or don’t copy the whole line of your pre-tested commands and after you press enter BANG, you’ve lost connection and start sweating. You know the feeling, right? Me neither…

New website - powered by Jekyll

Thu, 06 Apr 2017 00:00:00 +0000

I’ve recently moved my website from AnchorCMS to Jekyll. I didn’t think it was necessary to have a WordPress solution only for a personal blog that has less than 10 visits/month so I went for a static website that is not tied to mysql and php. With this change I’ve also switched from Apache2 to Nginx. I hope that with this change my tiny VPS is not going to need much resources in the future. I still have to tweak the CSS settings, so expect more changes soon enough.