So this is bugging me for a while and I'm just do dumb to get how I solve this, but here's the situation:
Given I take a local backup of my system daily and have a retention policy that keeps a backup of the past 7 days each, a backup of the past 4 weeks each and a backup of the past 6 month each. That's either 17 backups or less if you consider some backups being counted as a daily and weekly or as a weekly and monthly. But that's not that important.
The interesting part is, that I also take a remote backup of my local backup daily, which has the same retention policy, so it's cascading. Here there is obviously a huge overlap of backups, but I can't wrap my head around, how I calculate this.
Is anybody willing and/or interested to solve this for and with me?

I'm looking for a simply solution to monitor all my servers and systems using a single dashboard. I want to see metrics like CPU usage, used RAM and storage to see if something is wrong.
I just set up Node-Exporter, Prometheus and Grafana but haven't found an existing dashboard that shows multiple hosts at once. Now I looked into Checkmk and Zabbix but I feel like both are a little overpowered for what I'm looking for. Do you have any recommendations?

I made a simple script and timer for a friend to automatically switch between light and dark theme on Plasma. In case anybody needs this.

I created this small script and thought it might be useful to someone else. Any feedback is welcome!

I set up Headscale and Tailscale using Docker on a VPS, which I want to use as my public IPv4 and Reverse Proxy to route incoming traffic to my local network and e. g. my home server. I also set up Tailscale using Docker on my home server and connected both to my Headscale server.
I am able to ping on Tailscale container from the other and vice versa and set up --advertise-routes=192.168.178.0/24 on my home server as well as --accept-routes on my VPS, but I can't ping local IP addresses from my VPS. What am I missing?
Both container are connected to the host network, I have opened UDP ports 41641 and 3478 on my VPS.

I'm looking for an easy way to upload files from my Android smartphone to my home server. is there a - ideally dockerized - solution for that? Some simple web GUI where I can click on "Upload" and the files will be saved to a certain directory on my home server?

EDIT: I should've added that I want to do this remotely and not in my local network. I want to be able to send files from my Android smartphone from anywhere via the internet to my home server. That's why I thought about a services hosted on my server, which frontend I could access through my smartphone. But I might've answered my question already with the following: https://github.com/zer0tonin/Mikochi

EDIT #2: Thanks guys, I ended up creating my own Docker container running nextcloudcmd inspired by this: https://github.com/juanitomint/nextcloud-client-docker But I built the container from scratch and it's very minimalistic. I can publish it on my Gitlab when it's somewhat ready. Here's a little preview.

Dockerfile

FROM alpine:latest
RUN apk update && apk add nextcloud-client
COPY nc.sh .
RUN chmod +x ./nc.sh
VOLUME /data
CMD ./nc.sh

nc. sh (How can I prevent automatic hyperlinking?)

#!/bin/sh
while true
do
        nextcloudcmd /data https://${username}:${passwort}@${nextcloud-domain}
        sleep 300
done

I followed this tutorial to create local certificates for my home server, but now it failed to renew automatically and I have no clue waht to do. Can anybody assist me in debugging, please? https://notthebe.ee/blog/easy-ssl-in-homelab-dns01/

I'm using duckdns.org, added mydomain.duckdns.org and the local IP of my home server. In Nginx-Proxy-Manager I have created the respective wildcard certificate. The log of my NPM container reports the following:

[3/10/2024] [1:55:50 PM] [SSL      ] › ℹ  info      Renewing Let'sEncrypt certificates via DuckDNS for Cert #6: *.mydomain.duckdns.org, mydomain.duckdns.org
[3/10/2024] [1:55:50 PM] [SSL      ] › ℹ  info      Command: certbot renew --force-renewal --config "/etc/letsencrypt.ini" --work-dir "/tmp/letsencrypt-lib" --logs-dir "/tmp/letsencrypt-log" --cert-name "npm-6" --disable-hook-validation --no-random-sleep-on-renew 
[3/10/2024] [1:55:50 PM] [Global   ] › ⬤  debug     CMD: certbot renew --force-renewal --config "/etc/letsencrypt.ini" --work-dir "/tmp/letsencrypt-lib" --logs-dir "/tmp/letsencrypt-log" --cert-name "npm-6" --disable-hook-validation --no-random-sleep-on-renew 
[3/10/2024] [1:55:53 PM] [Express  ] › ⚠  warning   Saving debug log to /tmp/letsencrypt-log/letsencrypt.log
Failed to renew certificate npm-6 with error: The DNS response does not contain an answer to the question: mydomain.duckdns.org. IN TXT
All renewals failed. The following certificates could not be renewed:
  /etc/letsencrypt/live/npm-6/fullchain.pem (failure)
1 renew failure(s), 0 parse failure(s)

I noticed my home servers SSD running out of space and it ended up being my Jellyfin Docker container which wasn't clearing the directory for transcodes in /var/lib/jellyfin/transcodes correctly.

I simply created a new directory on my media hard drive and bind mounted the above mentioned directory to it. Now Jellyfin got over 1 TB of free space to theoretically clutter. To prevent this I simply created a cronjob to delete old files in case Jellyfin isn't.

@daily /usr/bin/find /path/to/transcodes -mtime +1 -delete

Easy!

I got a bunch of self-hosted stuff and use a VPS that has a public IPv4 to access my services because my home network has only DS-Lite. My home server ist connected to the VPS using Wireguard.
Now I want to connect my Smartphone to my VPN to be able to access some local services remotely. I'm able to add a second peer to the Wireguard config on the VPS, but I'm struggeling to configure the AllowedIPs correctly.
The VPS apparently needs AllowedIPs 10.0.0.0/24 and 192.168.178.0/24, but the Smartphone as well for both to redirect request into my home network. But it's not possible to configure the same IP ranges for two peers. What do I do?

EDIT: Solved: https://iliasa.eu/wireguard-how-to-access-a-peers-local-network/