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📅 Date: 2025-08-14
🔧 Tools: NetworkManager, ip, dhclient, rfkill, systemctl, wpa_supplicant, SSH, ssh-keygen
How It Started
I was setting up a fresh Debian 13 system on my server and wanted to migrate from using wpa_supplicant manually to managing my connection with NetworkManager. Along the way, I also began syncing my workflow between my Mac and the server, using SSH.
The Problem
NetworkManager broke the IP settings when I tried to restart it.
SSH wouldn’t connect after the server rebooted because IP addresses kept changing (e.g. from .121 back to .120, which conflicted with saved keys on my Mac).
Even after installing all the firmware and ensuring no blocks via rfkill, NetworkManager couldn’t manage the connection because wpa_supplicant was running independently.
The Fix
Manual IP Assignment (before DHCP setup):
sudo ip addr add 192.189.156.120/24 dev wlp3s0
sudo ip link set wlp3s0 up
sudo ip route add default via 192.189.156.1
echo "nameserver 1.1.1.1" | sudo tee /etc/resolv.conf
Install DHCP Client:
sudo apt install isc-dhcp-client
sudo ip link set wlp3s0 up
sudo dhclient -r wlp3s0
sudo dhclient wlp3s0
Check Internet:
ip a
ping 8.8.8.8
ping google.com
Verify Wi-Fi Module Status:
sudo apt install rfkill
rfkill list
Disable wpa_supplicant Process:
sudo systemctl stop wpa_supplicant
sudo systemctl disable wpa_supplicant
Later: sudo systemctl mask wpa_supplicant (for hard stop)
Fix SSH Key Conflict on Mac:
ssh-keygen -R 192.189.156.120
Reconnect to update known_hosts
Comment Out Auto-wpa_supplicant Launch:
Edit /etc/network/interfaces and comment out any lines that autostart wpa_supplicant
Stress Test:
Performed 5 reboots. Verified that IP remains stable (e.g., 192.189.156.120) only after masking wpa_supplicant and removing DHCP-based IP churn.
What I Learned
wpa_supplicant can launch outside of NetworkManager and interfere.
mask in systemctl completely disables the unit, redirecting it to /dev/null.
DHCP client assigns dynamic IPs on reboot unless static configuration is forced.
ssh-keygen -R is a lifesaver for known_hosts mismatch.
/etc/network/interfaces still matters in CLI-only Debian setups.
rfkill is critical for diagnosing Wi-Fi module blocks.
✍ Personal Note:
This was an interesting experience, because I made a lot of unnecessary moves. Like with every beginning - just like in Kendo - before you can strike properly, you’ll make a bunch of mistakes. But all of them are worth it.
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