How to make NetworkManager use `/etc` configs and where `/run` connections come from?

I have a Petalinux board (a Trenz Electronic with an AMD/Xilinx Zynq UltraScale+ MPSoC) which boots up with a wrong network connection config (no DHCP). It has no configs in /etc:

$ ls /etc/NetworkManager/system-connections/
$

After configuring the connection with sudo nmcli con mod eth0 ... it works fine. (I modify the ipv4 and ipv6 config, like [here on stackoverflow](https://stackoverflow.com/questions/60654764/switch-from-static-ip-to-dhcp-using-nmcli/60668424#60668424).) And it creates a permanent config file in /etc:

/etc/NetworkManager/system-connections/eth0.nmconnection

But, after a reboot NetworkManager creates a new /run config, which somehow takes precedence over my connection in /etc:

$ nmcli -f TYPE,FILENAME,UUID,NAME,DEVICE connection
TYPE      FILENAME                                                  UUID                                  NAME  DEVICE 
ethernet  /run/NetworkManager/system-connections/eth0.nmconnection  99e39a32-c0ab-4b3f-be16-75a9bdff1277  eth0  eth0   
loopback  /run/NetworkManager/system-connections/lo.nmconnection    5d84c484-4214-47e4-8f00-01f7730200b3  lo    lo     
ethernet  /etc/NetworkManager/system-connections/eth0.nmconnection  fb365147-6ad9-47a0-a5c8-fbea10080ece  eth0  --

Here, the rogue 99e39a32 from /run got connected to the eth0 device, and my /etc connection config fb365147 stays idle. How to correctly and permanently save a connection config in NetworkManager, or make it use /etc config as the only template for the eth0 connection? Where does it even get the configs for /run? How come it does not use /etc to create /run configs? There are posts saying the NetworkManager creates connections per user. I.e. the suggestion was something like /etc is root and somehow other connections get used for my user. But I don't think that's the case here. nmcli does not let me modify a connection without root permissions. There is a number of similar questions on the internet: (https://unix.stackexchange.com/questions/501260/where-does-network-manager-store-settings) (I don't have /etc/netplan file which is mentioned in a comment there), (https://stackoverflow.com/questions/77558991/how-to-stop-network-manager-creating-connections-under-run-networkmanager-syste) , (https://superuser.com/questions/1404124/how-do-i-make-persistent-changes-with-nmcli-in-non-interactive-mode) . But they don't help in my case. **Update:** There is some info how the /run config comes about thanks to the log journalctl -u NetworkManager after booting the computer with [loggin] level=TRACE in /etc/NetworkManager/NetworkManager.conf:

NetworkManager:   [1734374462.9312] device (eth0): carrier: link connected
NetworkManager:  [1734374462.9313] ethtool: ETHTOOL_GSET, eth0: success
NetworkManager:  [1734374462.9317] device[e5c0e28febbc1b13] (eth0): unmanaged: flags set to [platform-init,!user-settings=0x4/0x14/unmanaged/unrealized], set-managed [user-settings=0x10])
NetworkManager:  [1734374462.9318] device[e5c0e28febbc1b13] (eth0): unmanaged: flags set to [!platform-init,!user-settings=0x0/0x14/managed/unrealized], set-managed [platform-init=0x4])
NetworkManager:  [1734374462.9318] device[e5c0e28febbc1b13] (eth0): unmanaged: flags set to [!sleeping,!platform-init,!user-settings=0x0/0x15/managed/unrealized], set-managed [sleeping=0x1])
NetworkManager:  [1734374462.9319] dbus-object[e5c0e28febbc1b13]: export: "/org/freedesktop/NetworkManager/Devices/2"

NetworkManager:   [1734374462.9329] manager: (eth0): new Ethernet device (/org/freedesktop/NetworkManager/Devices/2)
NetworkManager:  [1734374462.9349] settings: auto-default: cannot create auto-default connection for device eth0: already has a profile
 [1734374462.9356] Connection 'eth0' differs from candidate 'eth0' in ipv4.addresses, ipv4.gateway, ipv4.method
NetworkManager:  [1734374462.9357] manager: (eth0): assume: generated connection 'eth0' (b807ebb2-d7a5-4b26-82c1-c321a6e7d5ba)
NetworkManager:  [1734374462.9357] device[e5c0e28febbc1b13] (eth0): assume-state: set guess-assume=0, connection=(null)
NetworkManager:  [1734374462.9370] keyfile: commit: b807ebb2-d7a5-4b26-82c1-c321a6e7d5ba (eth0) added as "/run/NetworkManager/system-connections/eth0.nmconnection" (nm-generated,volatile,external)

I guess the question now is what it means by Connection 'eth0' differs from candidate 'eth0' ... - what is that candidate? I.e. probably there is some more config for the eth0 device itself, and when the /etc config conflicts with that one, NetworkManager creates a new one? I tried adding this file with no change in the behavior (it's probably deprecated):

$ cat /etc/network/interfaces
auto eth0
iface eth0 inet dhcp

**Update 2:** Just to point out, I have tried adding no-auto-default config, but it made no difference in this case:

/etc/NetworkManager/NetworkManager.conf

[main]
no-auto-default=*
# or no-auto-default=eth0

And adding the connection in /etc/network/interfaces also did not help:

# Wired interfaces
auto eth0
iface eth0 inet dhcp
	hwaddress ether

I think, as @telcoM suggested, it is a Petalinux-specific behavior. You define the settings for the eth0 device when the image is built (and apparently NetworkManager can somehow read settings from the device or what?), and [you cannot modify ethernet settings in Petalinux after the image has been built](https://adaptivesupport.amd.com/s/question/0D54U000089gXtiSAE/how-can-i-change-the-network-ip-address-in-the-running-petalinux-on-zynq-mpsoc?language=en_US) . Probably, there is nothing that you can modify in uboot ZynqMP> console either. So, what I ended up doing is: [rename my connection](https://wrightrocket.blogspot.com/2018/11/network-manager-nmcli.html) to eth0dhcp and add a systemd unit that connects it after the boot.

sudo nmcli c mod fb365147-6ad9-47a0-a5c8-fbea10080ece con-name eth0dhcp

The connection config looks like: $ sudo cat /etc/NetworkManager/system-connections/eth0.nmconnection [connection] id=eth0dhcp uuid=fb365147-6ad9-47a0-a5c8-fbea10080ece type=ethernet autoconnect=false interface-name=eth0 timestamp=1734377647 [ethernet] mac-address= [ipv4] method=auto [ipv6] addr-gen-mode=default method=auto [proxy] And the one-shot systemd unit: [Unit] Description=UP the eth0dhcp for eth0 after boot After=network.target Requires=network.target [Service] Type=oneshot RemainAfterExit=yes User=root ExecStart=nmcli con up eth0dhcp SuccessExitStatus=0 Restart=on-failure RestartSec=20 StartLimitInterval=300 StartLimitBurst=5 [Install] WantedBy=multi-user.target It's enough of a workaround in my case. Later we'll just build images with whatever settings that are needed.