I've apparently "broken" network access to one of my Debian 'bookworm' systems that run on Raspberry Pi hardware. This resulted from my apparent lack of understanding of details wrt how the various "network tools" operate. The broken system is a "headless" unit; I can no longer make an SSH connection to it. It doesn't even respond to a ping. I'm raising this question here in the faint hope someone can explain if there's a way to regain SSH access without making any changes to the system. My current recourse is to remove the NVME SSD, and mount it on another system to correct the configuration error, or connect a monitor & keyboard, but these are difficult due to lack of hardware/cables, etc. What I did: Got "fed up" with NM's arcane nmcli interface, and thought, "there's got to be a better way". I read [this page on Debian's website](https://wiki.debian.org/NetworkManager) ; specifically: >NetworkManager will only handle interfaces not declared in /etc/network/interfaces I interpreted this to mean that if I declared my WiFi interface (wlan0) in /etc/network/interfaces, then NetworkManager would "step away", and systemd would use ifup, ifdown, etc to manage wlan0 IAW the contents I added to /etc/network/interfaces. Here's the contents of the interfaces file I created:

iface wlan0 inet static
    address 192.168.1.222
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 192.168.1.1

After a reboot I found I could no longer access this system via SSH. I have two questions: 1. Is there any way to regain SSH access without making changes to the system? 2. Why did the data I entered in /etc/network/interfaces fail to yield a working wifi connection?

So I have an embedded system I've built with yocto. I'm trying to enable DHCPv6. But when I try to bring the interface online, ifup says it can't find DHCPv6 software, even though dhcpcd is installed. And dhcpcd works if I run it manually.

root@1234:~# cat /etc/network/interfaces
auto lo
iface lo inet loopback

auto eth0
iface eth0 inet static
        address 192.168.5.80
        netmask 255.255.255.0
        gateway 192.168.5.1

iface eth1 inet6 dhcp

root@1234:~# ip a show dev eth1
8: eth1:  mtu 1500 qdisc noqueue qlen 1000
    link/ether ce:e6:83:59:f1:93 brd ff:ff:ff:ff:ff:ff
    inet 169.254.23.45/16 brd 169.254.255.255 scope global noprefixroute eth1
       valid_lft forever preferred_lft forever
    inet6 fe80::468b:6249:e50b:a437/64 scope link
       valid_lft forever preferred_lft forever

root@1234:~# which dhcpcd
/sbin/dhcpcd

root@1234:~# ifup eth1
No DHCPv6 client software found!
ifup: failed to bring up eth1

root@1234:~#

Note that eth1 is just a dummy interface for now, so that I don't break my ssh connection messing with eth0, which is really where I want to add DHCPv6.

I came accross the following bit of network conf and the part I don't get is the keyword **network**. Given that netmask is fed, what is the purpose of network ? Disclaimer : I'm not a guru of network configuration, so sorry i the question seems dumb. On Debian Jessie(8)

auto eth0
iface eth0 inet static
        address xx.201.4.132
        netmask 255.255.255.192
        network xx.201.4.128
        gateway xx.201.4.129

auto eth1
iface eth1 inet static
        address xx.201.69.4
        netmask 255.255.255.192
        network xx.201.69.0

I searched thoroughly in the manpage, this keyword is never mentionned. I've seen a mention of it in the Debian Wiki page on Network Comfiguration but that's all: > ### Configuring the interface manually > > If you're configuring it manually then something like this will set the default gateway (network, broadcast and gateway are optional):

I am using debian ifupdown’s mappings, with guessnet, to connect to the “right” WiFi network wherever I am. Here is an excerpt of my /etc/network/interface: mapping wlp2s0 script /usr/sbin/guessnet-ifupdown map autofilter: true map default: wlp2s0-default iface wlp2s0-tgv-inoui inet dhcp guessnet test wireless essid _SNCF_WIFI_INOUI wpa-conf /etc/wpa_supplicant/wpa_supplicant_minimal.conf wpa-driver nl80211,wext wpa-ssid _SNCF_WIFI_INOUI wpa-key-mgmt NONE openvpn home_client I also use unbound as a local caching DNS resolver. When I am connected to the _SNCF_WIFI_INOUI WiFi network, I’d like to forward DNS requests for the sncf. zones to the resolver provided by the DHCP server, since it provides different answers from the public servers (which I need to get the information specific to the train I am traveling in). As far as I know, isc-dhcp-client uses hooks that can be called when it gets answers for the DHCP server. I guess I could write one to configure unbound as needed. But how can I ensure this only happens for the wlp2s0-tgv-inoui logical interface? Is there a way I can get the logical interface when running the hook?

In a device with Debian BookWorm 12.5, I want to enable and disable a static IP using a Node application at runtime. The /etc/network/interfaces is the following : auto lo iface lo inet loopback ifconfig gives the following output : ~# ifconfig end0: flags=4163 mtu 1500 inet 192.168.109.176 netmask 255.255.255.0 broadcast 192.168.109.255 inet6 fe80::7376:77ae:719e:249f prefixlen 64 scopeid 0x20 ether f8:dc:7a:3e:8d:bb txqueuelen 1000 (Ethernet) RX packets 1155 bytes 392299 (383.1 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 519 bytes 84713 (82.7 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 lo: flags=73 mtu 65536 inet 127.0.0.1 netmask 255.0.0.0 inet6 ::1 prefixlen 128 scopeid 0x10 loop txqueuelen 1 (Local Loopback) RX packets 344 bytes 23930 (23.3 KiB) RX errors 0 dropped 0 overruns 0 frame 0 TX packets 344 bytes 23930 (23.3 KiB) TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0 Trying to turn-down the end0 interface, I get the following : ~# ifdown end0 ifdown: interface end0 not configured Then, I modify the /etc/network/interfaces as following : auto lo iface lo inet loopback auto end0 iface end0 inet static address 192.168.0.15 netmask 255.255.255.0 gateway 192.168.109.254 Trying to turn-up the interface with ifup end0, I get no error but the ifconfig output is the same as before. Trying again with ifup, I get the following : ~# ifup end0 ifup: interface end0 already configured and ifconfig gives the same output as before. I tried also to mess things up using ifconfig end0 down, service NetworkManager restart and service networking restart , but I continue to get undetermined behaviour, specially if I try to turn it down and up again when changing the interfaces file rolling back to dhcp configuration (i.e. without any reference to end0). What am i missing?

This is my /etc/network/interfaces file: auto bond0 iface bond0 inet manual address 10.66.7.11/24 gateway 10.66.7.1 bond-mode 802.3ad bond-slaves eth2 eth3 bond-miimon 100 bond-downdelay 200 bond-updelay 400 bond-lacp-rate 1 up ifconfig bond0 10.66.7.11/24 up when I bring the bond0 interface up, it works, but the default gateway is not set # route -n Destination Gateway Genmask Flags Metric Ref Use Iface 10.66.7.0 0.0.0.0 255.255.255.0 U 0 0 0 bond0 I have to set the default gateway manually, and then everything works fine: route add default gw 10.66.7.1 bond0 #route -n Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 10.66.7.1 0.0.0.0 UG 0 0 0 bond0 10.66.7.0 0.0.0.0 255.255.255.0 U 0 0 0 bond0 why is my default gateway not set automatically, when I have it defined in the /etc/network/interfaces file ?

Here is the content of /etc/network/interfaces: auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp post-up /etc/network/if-up.d/sshstart And sshstart is a script with the following in it: curl something something darkside send a file over ftps in the background & /usr/bin/autossh -M 0 -f -N -o ServerAliveInterval=15 -o ServerAliveCountMax=3 -R 127.0.0.1:2005:127.0.0.1:22 -R 192.168.1.10:2006:192.168.2.110:1912 -L 127.0.0.1:5249:192.168.1.212:5249 username@17.16.15.2 -p 8080 When the machine reboots, the curl command is executed multiple times, the file ends up 2 or 3 times on the ftp server and when I look at the processes it seems like there are multiple instances of autossh running... Not sure if this is how autossh does things or not, but for sure curl shouldn't upload the file multiple times. My hunch is that the whole sshstart script is ran multiple times but I don't understand why. I tried searching for details on the network setup process at boot but all I could find was syntax information for the interfaces file. Can someone help please? Thank you. **---Edit---**

As suggested bellow I have modified my interfaces file as follow (removed the empty lines above post-up): auto lo iface lo inet loopback auto eth0 iface eth0 inet dhcp post-up /etc/network/if-up.d/sshstart And added the following line to sshstart: echo $(date)>>/run/shm/sshstart.log Here is the content of /run/shm/sshstart.log after a reboot: Wed Oct 29 08:07:00 EDT 2014 Wed Oct 29 08:07:07 EDT 2014 Wed Oct 29 08:07:07 EDT 2014 Wed Oct 29 08:07:07 EDT 2014 So its been ran 4 times :( what's going on?

I'm using Debian Buster and I have two interfaces configured: eth0 and wwan0 (broadband modem). Here's the relevant part of my interfaces file:

# The primary network interface
auto eth0
iface eth0 inet dhcp

# Do not bring up wwan0 automatically
allow-hotplug wwan0
iface wwan0 inet dhcp
        pre-up until [ -h /dev/ublox00 ]; do sleep 1; done && echo $'AT+UCEDATA=1,0\r\n' > /dev/ublox00 && sleep 2
        post-down echo $'AT+CGACT=0\r\n' > /dev/ublox00

I've noticed that when I want to bring wwan0 down, it also releases the IP address for eth0:

$ sudo ifdown -v wwan0
ifdown: configuring interface wwan0=wwan0 (inet)
/bin/run-parts --verbose /etc/network/if-down.d
run-parts: executing /etc/network/if-down.d/wpasupplicant
/sbin/dhclient -4 -v -i -r -pf /run/dhclient.wwan0.pid -lf /var/lib/dhcp/dhclient.wwan0.leases -I -df /var/lib/dhcp/dhclient6.wwan0.leases wwan0
Killed old client process
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/ 

Listening on LPF/eth0/98:f0:7b:98:7a:89
Sending on   LPF/eth0/98:f0:7b:98:7a:89
Listening on LPF/wwan0/ee:bc:6c:be:6d:7c
Sending on   LPF/wwan0/ee:bc:6c:be:6d:7c
Sending on   Socket/fallback
DHCPRELEASE of 192.168.1.101 on eth0 to 192.168.1.1 port 67
DHCPRELEASE of 100.68.214.247 on wwan0 to 100.68.214.248 port 67
/sbin/ip link set dev wwan0 down
/bin/run-parts --verbose /etc/network/if-post-down.d
run-parts: executing /etc/network/if-post-down.d/hostapd
run-parts: executing /etc/network/if-post-down.d/wireless-tools
run-parts: executing /etc/network/if-post-down.d/wpasupplicant
echo $'AT+CGACT=0\r\n' > /dev/ublox00

And requests it again after bringing the interface up:

$ sudo ifup -v wwan0
ifup: configuring interface wwan0=wwan0 (inet)
until [ -h /dev/ublox00 ]; do sleep 1; done && echo $'AT+UCEDATA=1,0\r\n' > /dev/ublox00 && sleep 2
/bin/run-parts --exit-on-error --verbose /etc/network/if-pre-up.d
run-parts: executing /etc/network/if-pre-up.d/hostapd
run-parts: executing /etc/network/if-pre-up.d/wireless-tools
run-parts: executing /etc/network/if-pre-up.d/wpasupplicant

/sbin/dhclient -4 -v -i -pf /run/dhclient.wwan0.pid -lf /var/lib/dhcp/dhclient.wwan0.leases -I -df /var/lib/dhcp/dhclient6.wwan0.leases wwan0
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/ 

Listening on LPF/eth0/98:f0:7b:98:7a:89
Sending on   LPF/eth0/98:f0:7b:98:7a:89
Listening on LPF/wwan0/ee:bc:6c:be:6d:7c
Sending on   LPF/wwan0/ee:bc:6c:be:6d:7c
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3
DHCPDISCOVER on wwan0 to 255.255.255.255 port 67 interval 6
DHCPOFFER of 192.168.1.101 from 192.168.1.1
DHCPREQUEST for 192.168.1.101 on eth0 to 255.255.255.255 port 67
DHCPOFFER of 100.68.214.247 from 100.68.214.248
DHCPREQUEST for 100.68.214.247 on wwan0 to 255.255.255.255 port 67
DHCPACK of 100.68.214.247 from 100.68.214.248
bound to 100.68.214.247 -- renewal in 74796 seconds.
/bin/run-parts --exit-on-error --verbose /etc/network/if-up.d
run-parts: executing /etc/network/if-up.d/wpasupplicant

The commands sudo ifdown eth0 and sudo ifup eth0 operate on eth0 only as expected. Please help me find the problem. My ifupdown version is 0.8.35.

TL;DR

sudo cp -p /etc/network/if-up.d/resolved /etc/network/if-up.d/.resolved.broken-orig

#Edit /etc/network/if-up.d/resolved and take out the extraneous quotes on lines 48 and 52
#The fix looks like:
diff /etc/network/if-up.d/.resolved.broken-orig /etc/network/if-up.d/resolved
48c48
 $DNS="$NEW_DNS"
52c52
 $DOMAINS="$NEW_DOMAINS"

At least, this appears to be effective. ---- Recently upgraded an older system to Ubuntu 22.04.1 LTS via do-release-upgrade and ran into DNS issues, error messages were:

nslookup google.com
Server:		127.0.0.53
Address:	127.0.0.53#53

** server can't find google.com: SERVFAIL

and

/etc/network/if-down.d/resolved: 12: mystatedir: not found
/etc/network/if-up.d/resolved: 71: DNS: not found
/etc/network/if-up.d/resolved: 1: /run/network/ifupdown-inet-em1: DNS=8.8.8.8: not found
/etc/network/if-up.d/resolved: 2: /run/network/ifupdown-inet-em1: DOMAINS=local_search_domain.com: not found
Failed to parse DNS server address: DNS
Failed to set DNS configuration: Invalid argument

when attempting to run an nslookup via a network connection (em1) defined in /etc/network/interfaces prior to the system upgrade. After a period of self-soothing I located https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1981103 and https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1910273 which helped enhance my calm. It appears that, at a minimum, the errors encountered were due to a pair of typos in /etc/network/if-up.d/resolved which are easily fixed with a text editor; after manually removing the extraneous quotes I am able to bring up the network interface and query DNS servers. It's unclear to me if there are other issues with the ifupdown package currently shipped by Ubuntu 22.04.1 LTS (0.8.36+nmu1ubuntu3) or the manual edit I described above. Are there any documented fixes that don't involve editing lines 48 and 52 of /etc/network/if-up.d/resolved or is this the best workaround currently available for legacy systems that have been upgraded to Ubuntu 22.04.1 LTS?

I frequently find myself sitting in front of various different Linux installations and need to check or change network settings. They are different versions from different distributions (mostly debian and opensuse, but also ubuntu and derived variants) in varying states of customization, which means i can't make reliable assumptions about their configurations. So how can i find out in a easy and robust (that is distro and version independent) way, which service is used to manage network interfaces and related network settings. (like NetworkManager, Systemd-networkd or ifup/down) -> Ideally with basic system tools The System can find out which service is to be used/started at system startup, so there has to be either a command that tells me or a config file where i can look it up. I am aware, that similar questions have been asked numerous times, but all answers i could find boil down to one of two not very helpful gists: - either the author mentioned their distro/version and someone told them, which program is probably used - or they were told to basically try each possibility until they found the running manager both of which i consider neither very reliable nor safe. (not to mention that trial and error is very time consuming)

I have 2 ethernet ports bridged as follows (/etc/network/interfaces.d/br0):

auto br0
iface br0 inet dhcp
        bridge_ports enp1s0 enp2s0
        bridge_fd 0
        bridge_waitport 0
        bridge_stp off

auto br0:1
iface br0:1 inet static
        address 169.254.10.50
        netmask 255.255.255.0

In this instance, a PC and router are always in a combined unit. The router has DHCP enabled, but takes longer to boot than the PC. enp1s0 is in LAN port of the router, enp2s0 is connected to another device that will ALWAYS have an IP address of 169.254.10.49. When the combined unit is rebooted, if the router does not finish its boot process before the PC has booted, br0 will never be assigned an IP address. What I need to happen, ideally, is that at any point after the system has booted, if a DHCP server is available, br0 will be assigned an IP address. Can I configure the bridge to get an IP address after the DHCP server becomes available?

Hello (beginner to linux networking), I'm trying to build a lab in VirtualBox with a Debian GLPI server for school, the VM has 2 network interfaces : a NAT one in dhcp (eth0) and the other one (intern) is in static for local network (eth1). Dumb question but what is the difference between enp0s and eth ? I tried this config : auto eth0 iface eth0 inet dhcp allow-hotplug eth0 auto eth1 iface eth1 inet static allow-hotplug eth1 address 172.16.2.56 netmask 255.255.255.192 network 172.16.2.0 gateway 172.16.2.62 broadcast 172.16.2.63 I lost internet when making changes to the eth1 card which is unfortunate cause i need it to build GLPI, i tried different confs but cannot make the networking service restart, ifup is breaking on the address line : misplaced option. Basically i want my NAT to come back and stay up so i can have internet on my VM + having eth1 for local purpose and hosting the GLPI ITSM service. I don't know if i made it clear, if asked i will give you details, thanks for your help in advance.

I have Ubuntu 20.04 where I gave all network functions to ifupdown. 1 of my interface got network parameters by dhclient:

#/etc/network/interfaces
allow-hotplug enp2s0
auto enp2s0
iface enp2s0 inet dhcp

Dhclient starts with such parameters:

#ps -Af | grep dhclient

/sbin/dhclient -1 -4 -v -i -pf /run/dhclient.enp2s0.pid -lf /var/lib/dhcp/dhclient.enp2s0.leases -I -df /var/lib/dhcp/dhclient6.enp2s0.leases enp2s0

Dhclient version:

# dhclient --version
isc-dhclient-4.4.1

Client config:

# cat /etc/dhcp/dhclient.conf 
option rfc3442-classless-static-routes code 121 = array of unsigned integer 8;

send host-name = gethostname();
request subnet-mask, broadcast-address, time-offset, routers,
	domain-name, domain-name-servers, domain-search, host-name,
	dhcp6.name-servers, dhcp6.domain-search, dhcp6.fqdn, dhcp6.sntp-servers,
	netbios-name-servers, netbios-scope, interface-mtu,
	rfc3442-classless-static-routes, ntp-servers;

timeout 60;
retry 60;
reboot 10;
reject 10.100.0.2;

Tired to google how to change parameters for dhclient start(I want to start it without -1 and in daemon mode), like this:

/sbin/dhclient -nw -4 -v -pf /run/dhclient.enp2s0.pid -lf /var/lib/dhcp/dhclient.enp2s0.leases -I -df /var/lib/dhcp/dhclient6.enp2s0.leases enp2s0

How I can do it? Thank you!

I have a Sipeed RV 86 device, which is a RISCV 64bit. On this,I run a minimal Debian OS, that let's me log in via the USB interface, as the device shows up as ttyUSB0 on the host Linux PC. When I then try to bring up networking, I stumble on this error:

# ifconfig 
lo: flags=73  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 1630  bytes 89377 (87.2 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 1630  bytes 89377 (87.2 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

usb0: flags=4099  mtu 1500
        ether e2:95:8c:23:89:85  txqueuelen 1000  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

# ifup usb0
ifup: unknown interface usb0

After making the interface known in /etc/network/interfaces.d/usb0 using:

auto usb0
iface usb0 inet dhcp

...I get:

# ifup usb0
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/ 

Listening on LPF/usb0/e2:95:8c:23:89:85
Sending on   LPF/usb0/e2:95:8c:23:89:85
Sending on   Socket/fallback
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 5
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 14
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 9
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 8
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 14
DHCPDISCOVER on usb0 to 255.255.255.255 port 67 interval 11
No DHCPOFFERS received.
No working leases in persistent database - sleeping.
root@licheerv:/etc/network/interfaces.d#

I know that my DHCP server is running, and working, as other clients work fine. I also see the network LED on the device blink, so there is activity. How can I get networking going on this device? UPDATE 1 ======== During boot, I also see this:

[    **] A start job is running for Raise network interfaces (27s / 5min 15s)
[   33.761420] ldob: disabling

UPDATE 2 ======== Unfortunately, the TPLINK dhcp server logging is severely lacking... it doesn't display much, other than:

On my current Debian system I use VLAN tagging and I create bridges br-wan and br-lan that I use for LXC containers: auto lo br-lan br-wan iface lo inet loopback iface br-wan inet manual     bridge_ports eth0.3     bridge_maxwait 0 iface br-lan inet static     address 192.168.200.10 netmask 255.255.255.0 gateway 192.168.200.1 bridge_ports eth0.2 bridge_maxwait 0       iface eth0.1 inet static address 10.7.1.10 netmask 255.255.255.0 Now I would like to add a KVM guest that gets transparent access to eth0 and in turn uses VLAN tagging internally (for example, to create a virtualized router routing between eth0.2 and eth0.3). To test, I did the following: brctl addbr br-master brctl addif eth0 And then I created a KVM guest with --network=bridge=br-master,model=virtio which creates an interface vnet0 that is also added as bridge port to br-master. Inside the guest added the VLAN interfaces.   On the host, I see tagged packets in vnet0 (tcpdump -i vnet0 -e vlan) and br-master (tcpdump -i br-master -e vlan).   However, the traffic never reaches eth0 on the host. I am sure the story is not that simple. How can I add such a VLAN-transparent "master bridge" to my system, without disrupting my old config?

I have a virtual box (6.1) with ubuntu minimal. in the settings of the virtual machine in the network section, "Bridged Adapter" is selected. root@ubuntu:/home/mista# dmesg -T|head -1 [Sun Oct 24 10:56:10 2021] Linux version 5.4.0-89-generic (buildd@lgw01-amd64-044) (gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)) #100-Ubuntu SMP Fri Sep 24 14:50:10 UTC 2021 (Ubuntu 5.4.0-89.100-generic 5.4.143) root@ubuntu:/home/mista# ip a 1: lo: mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 inet 127.0.0.1/8 scope host lo valid_lft forever preferred_lft forever inet6 ::1/128 scope host valid_lft forever preferred_lft forever 2: enp0s3: mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 08:00:27:1e:5b:6d brd ff:ff:ff:ff:ff:ff inet 192.168.88.236/24 brd 192.168.88.255 scope global dynamic enp0s3 valid_lft 473sec preferred_lft 473sec inet6 fe80::a00:27ff:fe1e:5b6d/64 scope link valid_lft forever preferred_lft forever root@ubuntu:/home/mista# cat /etc/network/interfaces # interfaces(5) file used by ifup(8) and ifdown(8) # Include files from /etc/network/interfaces.d: source-directory /etc/network/interfaces.d auto lo iface lo inet loopback auto enp0s3 iface enp0s3 inet static address 192.168.88.236 netmask 255.255.255.0 gateway 192.168.88.1 root@ubuntu:/home/mista# ifdown enp0s3 ifdown: interface enp0s3 not configured root@ubuntu:/home/mista# ifup enp0s3 RTNETLINK answers: File exists ifup: failed to bring up enp0s3 root@ubuntu:/home/mista# systemctl status networking ● networking.service - Raise network interfaces Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled) Active: failed (Result: exit-code) since Sun 2021-10-24 11:24:35 MSK; 1min 39s ago Docs: man:interfaces(5) Process: 826 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=1/FAILURE) Main PID: 826 (code=exited, status=1/FAILURE) Oct 24 11:24:35 ubuntu systemd: Starting Raise network interfaces... Oct 24 11:24:35 ubuntu ifup: RTNETLINK answers: File exists Oct 24 11:24:35 ubuntu ifup: ifup: failed to bring up enp0s3 Oct 24 11:24:35 ubuntu systemd: networking.service: Main process exited, code=exited, status=1/FAILURE Oct 24 11:24:35 ubuntu systemd: networking.service: Failed with result 'exit-code'. Oct 24 11:24:35 ubuntu systemd: Failed to start Raise network interfaces. root@ubuntu:/home/mista# cat /run/network/ifstate lo=lo I tried to add the string "enp0s3=enp0s3" to /run/network/ifstate but it doesn't work. But /run - it's a virtual file system and the string with enp0s3 will be delete after reload daemons or reboot the server. Some people say that all configured interfaces should be displayed in /run/network/ifstate. But why, then, the enp0s3 interface is not displayed in the /run/network/ifstate if it is registered in the config ? And may be I have some mistake in config file? after reboot, the address 192.168.88.236/24 rises, but these commands do not work: ifup enp0s3 ifdown enp0s3 I don't understand why errors are coming out: root@ubuntu:/home/mista# ifdown enp0s3 ifdown: interface enp0s3 not configured root@ubuntu:/home/mista# ifup enp0s3 RTNETLINK answers: File exists ifup: failed to bring up enp0s3 Where ifup and ifdown can get the config to work with the interface except for the file /etc/network/interfaces? The file /etc/networks is empty.

I have been running Debian 10 a.k.a. Buster without issues. My problems started when all of a sudden, network connectivity dropped. At that point, NetworkManager was active. I stopped and disabled the service to exclude its interference. This PC runs KVM VMs in a bridged configuration:

$ sudo brctl show
bridge name	bridge id       STP     enabled	interfaces
br1     8000.7446a0a0d47b   no      eno1
                                    vnet0
                                    vnet1
                                    vnet2
                                    vnet3

My interfaces file looks like this (leaving out a few comments):

$ cat /etc/network/interfaces
(...)
# The loopback network interface
auto lo
iface lo inet loopback

#auto eno1
#iface eno1 inet manual

auto br1
iface br1 inet manual
bridge_ports eno1
address 192.168.1.27
netmask 255.255.255.0
gateway 192.168.1.1
dns-nameservers 192.168.1.16, 1.1.1.1

When I run systemctl restart networking, or ifdown br1; ifup br1, br1 ends up with no IP address, both eno1 and br1 are down, and there is no default route. Removing the hash signs on the eno1 lines has no effect. In my desperation, I added this line to the interfaces file: this line is illegal. When it comes **before** the loopback block, it causes an expected error message:

ifup: /etc/network/interfaces:7: misplaced option
ifup: couldn't read interfaces file "/etc/network/interfaces"

When it comes **after** it, it doesn't. It's as if ifupdown stopped reading after the loopback configuration. But putting the loopback block at the end of the file still doesn't configure br1. I haven't detected any non-printable characters or otherwise strange characters in the file. To cross the T's, here is the journal:

$ sudo journalctl -u -e networking
(...)
-- Reboot --
May 21 09:29:58 jupiter systemd: Starting Raise network interfaces...
May 21 09:29:59 jupiter ifup: Waiting for br1 to get ready (MAXWAIT is 32 seconds).
May 21 09:30:00 jupiter systemd: Started Raise network interfaces.

And setting STP on the bridge doesn't change the behaviour. How about ifup?

# type ifup
ifup is /usr/sbin/ifup
# file /usr/sbin/ifup
/usr/sbin/ifup: ELF 64-bit LSB pie executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=9ac8619bfa91d2b8901228595fa390826c9682c7, stripped

**How can I figure out why my network configuration is simply ignored?**