This just started like 4 or 5 days ago. I'm running Ubuntu 12.04 desktop, and after about 12 hours of uptime it seems the loopback device just stops working. If I do an ifconfig, it looks like it's still there, but if I ping localhost or 127.0.0.1, both fail. Also, pinging known DNS addresses (www.google.com) fail. But pinging by IP works fine.
The rest of the networking features seem unphased. I can still reach the Samba share from my Windows machine. Also, I run an Apache server that is still reachable from the outside world. Looking at the resources monitor, the CPU and memory usage appear normal when this happens.
If I restart the machine, everything is fine again. For about 12 hours, until it happens again. Any ideas on what could be causing this or how to diagnose it? Thanks.
Edit: I ran the recommended diagnostics commands. Below is the output. I can't really make heads or tails of it though. Does anything look out of the ordinary?
~$ ip addr
1: lo: mtu 16436 qdisc noqueue state UNKNOWN
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: mtu 1500 qdisc pfifo_fast state UP qlen 1000
link/ether 00:1b:fc:64:dc:82 brd ff:ff:ff:ff:ff:ff
inet 192.168.1.132/24 brd 192.168.1.255 scope global eth0
inet6 fe80::21b:fcff:fe64:dc82/64 scope link
valid_lft forever preferred_lft forever
~$ netstat -rn
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0
169.254.0.0 0.0.0.0 255.255.0.0 U 0 0 0 eth0
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
~$ getent hosts localhost
127.0.0.1 localhost
~$ ping 127.0.0.1
PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.
^C
--- 127.0.0.1 ping statistics ---
572 packets transmitted, 0 received, 100% packet loss, time 575551ms
~$ ping6 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.020 ms
64 bytes from ::1: icmp_seq=2 ttl=64 time=0.023 ms
64 bytes from ::1: icmp_seq=3 ttl=64 time=0.025 ms
64 bytes from ::1: icmp_seq=4 ttl=64 time=0.021 ms
64 bytes from ::1: icmp_seq=5 ttl=64 time=0.028 ms
64 bytes from ::1: icmp_seq=6 ttl=64 time=0.025 ms
64 bytes from ::1: icmp_seq=7 ttl=64 time=0.023 ms
64 bytes from ::1: icmp_seq=8 ttl=64 time=0.026 ms
64 bytes from ::1: icmp_seq=9 ttl=64 time=0.021 ms
64 bytes from ::1: icmp_seq=10 ttl=64 time=0.028 ms
^C
--- ::1 ping statistics ---
10 packets transmitted, 10 received, 0% packet loss, time 8998ms
rtt min/avg/max/mdev = 0.020/0.024/0.028/0.002 ms
~$ ifconfig
eth0 Link encap:Ethernet HWaddr 00:1b:fc:64:dc:82
inet addr:192.168.1.132 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::21b:fcff:fe64:dc82/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:5537467 errors:0 dropped:0 overruns:0 frame:0
TX packets:7700200 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2390500721 (2.3 GB) TX bytes:8274946292 (8.2 GB)
Interrupt:23 Base address:0x4000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:1441430 errors:0 dropped:0 overruns:0 frame:0
TX packets:1441430 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:2084259522 (2.0 GB) TX bytes:2084259522 (2.0 GB)
ip addr,netstat -rn,getent hosts localhost,ping 127.0.0.1, andping6 ::1.