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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?


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...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? –  Grzegorz Dubicki Mar 1 at 8:33

2 Answers 2

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.

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I have had similar problem. My lo vanished after turning off IPv6 (via sysctl) and rebooting the server. To be more precise: it was being created but without any IP set up. So it was visible under ifconfig -a but not under plain ifconfig.

So in my case it helped to change /etc/network/interfaces loopback entry to:

auto lo
iface lo inet static

Update: actually after reboot my /etc/network/interfaces has been reset to previous value (by my VPS provider, probably) and I had to change it again and do ifdown lo, ifup lo and restart all my services that depend on loopback (= almost all of them). So it's not resolved yet but it is a workaround. I will update this answer if I find better solution.)

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Note that ifconfig is deprecated. Use ip addr show instead. –  the-wabbit Mar 1 at 8:58

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