Boot message - Failed to start

Update: solved (see below).

Booting up my installation of Debian Testing (Bookworm) I noticed this message:

 

 

[FAILED] Failed to start: Raise network interfaces.

See 'systemctl status networking.service' for detials.

Was this something bad? I hadn't noticed anything like it before. The word 'FAILED' in capital letters and red made me worried.

Systemd does not apparently keep a log of these boot messages. To find a failed command, issue the following command:

# systemctl --failed

  UNIT               LOAD   ACTIVE SUB    DESCRIPTION
● networking.service loaded failed failed Raise network interfaces

LOAD   = Reflects whether the unit definition was properly loaded.
ACTIVE = The high-level unit activation state, i.e. generalization of SUB.
SUB    = The low-level unit activation state, values depend on unit type.
1 loaded units listed.

To see networking.service messages, issue this command:

# journalctl -u networking.service --no-pager

-- Boot e29338dc96c041638d5b465983e41817 --
Oct 02 18:35:32 Toshiba-laptop ifup[618]: Cannot find device "eth0"
Oct 02 18:35:32 Toshiba-laptop ifup[552]: ifup: failed to bring up eth0
Oct 02 18:35:27 Toshiba-laptop systemd[1]: Starting Raise network interfaces...
Oct 02 18:35:29 Toshiba-laptop systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Oct 02 18:35:29 Toshiba-laptop systemd[1]: networking.service: Failed with result 'exit-code'.
Oct 02 18:35:29 Toshiba-laptop systemd[1]: Failed to start Raise network interfaces.

Well, that clears that up: there's no Ethernet cable plugged into this computer. 

 

Update: I found the source of this issue (Debian User Forums). It is not the system looking for an Ethernet connection that happens to be unplugged, but the system looking for an Ethernet connection that does not exist, due to some unexplained entries in a configuration file, namely:

/etc/network/interfaces.d/setup

The entries below were causing the system to try to bring up network interfaces at boot time. Commenting them out got rid of the "Failed" message.

auto lo 

iface lo inet loopback 

auto eth0 

iface eth0 inet dhcp/

The  only mystery now is what added those lines when they shouldn't be there? Suspicion at the moment falls on the Debian Live Non-Free installation media, which I used to install Debian Bullseye.