I just installed an Ubuntu 14.04 server, and I've discovered that there is no way to make any changes to the network configuration except by rebooting the server. This is on a stock install of Ubuntu 14.04 server, installed last week, with no changes made to it, and no new packages installed (since I can't reach apt-get).

ifconfig up/down seems to read from some kind of cache; at least, it ignores any changes I make to /etc/network/interfaces. I tried using it to change from DCHP to static for eth1, and nothing happened; eth1 continued to get its address from DHCP.

/etc/init.d/networking stop/restart/force-reload all fail with no error message.

How is this supposed to work on Ubuntu Server? Right now, it seems like network changes only take effect with a reboot.

(and please don't give me answers which involve network-manager; this is a headless server with no GUI. Thanks).


/etc/network/interfaces originally was:

# The primary network interface
auto eth1
iface eth1 inet dhcp

... this wasn't picking up gateway information from DHCP, even though my Ubuntu laptop picks it up just fine.

So I changed it to:

# The primary network interface
auto eth1
iface eth1 inet static

However, after doing ifconfig down/up, the IP address of eth1 did not change and the gateway did not get added to the route table. On a full restart of the system, the eth1 configuration was picked up just fine.

So it seems that ifconfig up ignores changes to /etc/network/interfaces.

  • Have you looked in /var/log/*? There should be error messages in /var/log/syslog or /var/log/udev. Hint: Cause the (mis)behavior, do ls -rlt /var/log, then inspect the last many lines of the last few files listed. – waltinator Aug 11 '14 at 22:30
  • There are no relevant error messages in syslog or udev that I can find. Running ifconfig up/down generates only the message that ipv6 isn't configured (which it's not, I'm using ipv4). – FuzzyChef Aug 11 '14 at 22:59
  • Are you running ifconfig up/down as root, or via sudo? If not, networking will be unaffected. What is in your /etc/network/interfaces file? – waltinator Aug 11 '14 at 23:20
  • /etc/network/interfaces: # The primary network interface auto eth1 iface eth1 inet static address netmask gateway Note that the above took effect just fine on a reboot of the system. – FuzzyChef Aug 12 '14 at 19:04
  • "Reboot" should be a last resort, I would think. @chili555 has a better answer. – waltinator Aug 13 '14 at 1:47

The correct way to get the system to re-read and use the changed /etc/network/interfaces file is:

sudo ifdown eth1 && sudo ifup -v eth1

The '-v' for verbose should produce output to judge if the changes were made successfully. Check:

ping -c3 www.google.com
  • This helped me diagnose the issue, but was not the actual answer. Hence, vote up but not accepted. – FuzzyChef Aug 14 '14 at 17:37

Based on follow-ups elsewhere, I found that it is indeed the case that Ubuntu will completely ignore changes in /etc/network/interfaces for a device which was previously defined and then changed. In order to get it to take a new configuration, you need to run the following:

ifdown {device}
ip addr flush dev {device}
ifup {device}

This is run between ifdown and ifup. Ideally, Ubuntu should add the flush to ifup.

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