I've had Ubuntu 12.04 on a server for the last several months, with everything working fine. Last night I did an aptitude update && aptitude safe-upgrade to bring in all the latest security changes, and now when I boot the server no lo device is created.

It brings up the physical ethernet interfaces correctly, and I can ping in and out of the machine on those interfaces, but nothing can connect to anything on either localhost or

ifconfig lists only eth0 and eth1.

No lo at all.

Here are the contents of /etc/network/interfaces:

# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
#NetworkManager#iface eth0 inet dhcp

Where should I be looking to diagnose and fix?


  • ...me too on 12.04.2. Machine boots fine, but no 'lo' shown by ifconfig. "ifup lo" brings it right up and then all is well (after stop/start of some servers that weren't happy without lo at boot.) You ever figure this out? – Craig Constantine Feb 25 '13 at 16:33
  • Please check your /etc/hosts. serverfault.com/questions/333269/… – Tinti Sep 3 '13 at 12:42
  • @quangdog I am pretty sure this has been long resolved/forgotten but in a slight chance it has not been: what is the output of ifconfig -a on this machine? – Greg Dubicki Mar 1 '15 at 8:33

I have had similar problem.

My lo didn't start automatically at boot (after turning off IPv6 via sysctl and rebooting the server).

My first workaround was to start it manually with ifup --force lo. But after that I had to restart most of my services as they didn't work properly without loopback.

Finally this old forum post helped me to find out the proper and permanent solution:

  1. sudo rm -rf /var/run/network/*
  2. sudo reboot

(Apparently there was some old .lock file there that prevented the loopback to start properly.)

  • Note that ifconfig is deprecated. Use ip addr show instead. – the-wabbit Mar 1 '15 at 8:58
  • nice find! never would have thought to look in there. – killthrush Jun 23 '15 at 15:30

If lo can be brought up manually with ifup lo but isn't brought up automatically, you should be able to put the command ifup lo in /etc/rc.local so it will start at each boot. Not an elegant solution but it should be a permanent solution.

  • Doesn't work for me. Also tried with --force (which works on interactive shell) but to no avail. – Greg Dubicki May 1 '15 at 17:36

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