I want to program an FPGA via JTAG and the xmd script connects to 127.0.0.1:3121 to do so. That worked nicely for months. After a reboot this connection suddenly didn't exist any more, I cannot ping 127.0.0.1 or localhost (still resolved to 127.0.0.1) any more either. ifconfig is missing "lo". I have entries for eth4 and eth5, my two network cards, but no lo. Full output is at the end of the question. Connections to and from other computers work fine. How do I get it running again?
I tried to start it manually but that doesn't change anything:
> ifup lo ifup: interface lo already configured > ifup --force lo (no output) This doesn't work either:
> route add -host 127.0.0.1 dev lo SIOCADDRT: No such device Some diagnosis output:
> route -n Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.153.1 0.0.0.0 UG 0 0 0 eth5 192.168.10.0 0.0.0.0 255.255.255.0 U 1 0 0 eth4 192.168.153.0 0.0.0.0 255.255.255.0 U 1 0 0 eth5 > cat /var/run/network/ifstate lo=lo > cat /etc/network/interfaces # interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet loopback > iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination Chain FORWARD (policy ACCEPT) target prot opt source destination Chain OUTPUT (policy ACCEPT) target prot opt source destination I don't have an /etc/iptables.conf
I also tried sudo rm -rf /var/run/network/* from this question. I did apt-get update and apt-get upgrade. No change.
> ifconfig 127.0.0.1 lo lo: Unknown host ifconfig: `--help' gives usage information. Output of ifconfig:
eth4 Link encap:Ethernet HWaddr 00:24:e8:45:8f:10 inet addr:192.168.10.2 Bcast:192.168.10.255 Mask:255.255.255.0 inet6 addr: fe80::224:e8ff:fe45:8f10/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:67 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:10916 (10.9 KB) Interrupt:21 Memory:f7fe0000-f8000000 eth5 Link encap:Ethernet HWaddr d8:eb:97:71:be:e5 inet addr:192.168.153.124 Bcast:192.168.153.255 Mask:255.255.255.0 inet6 addr: fe80::daeb:97ff:fe71:bee5/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:35392 errors:0 dropped:0 overruns:0 frame:0 TX packets:28754 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:20734790 (20.7 MB) TX bytes:4354467 (4.3 MB) Edit:
> ip link 1: ttyUSB0: <LOOPBACK> mtu 65536 qdisc noop state DOWN mode DEFAULT group default link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00 2: eth5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether d8:eb:97:71:be:e5 brd ff:ff:ff:ff:ff:ff 3: eth4: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000 link/ether 00:24:e8:45:8f:10 brd ff:ff:ff:ff:ff:ff 
ip linkinstead of the obsoleteifconfig? It will list all registered interfaces with their current status and you can try to bring them up usingip link set <interface> up