networking.service refuses to start on boot (failed to bring up lo, file exists)

Question

Since I attempted to set up an encrypted swap partition (Encrypted swap partition does not show up in /dev/mapper), I get an error during boot that the networking.service could not be started.

Here's the info I get when running the command described in the error message:

$ systemctl status networking.service 
? networking.service - Raise network interfaces
   Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled)
  Drop-In: /run/systemd/generator/networking.service.d
           ??50-insserv.conf-$network.conf
   Active: failed (Result: exit-code) since Mi 2016-08-10 22:57:45 CEST; 10min ago
     Docs: man:interfaces(5)
  Process: 4424 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=1/FAILURE)
  Process: 4417 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=l
 Main PID: 4424 (code=exited, status=1/FAILURE)

Aug 10 22:57:45 BC-AlkaliMetal systemd[1]: Starting Raise network interfaces...
Aug 10 22:57:45 BC-AlkaliMetal ifup[4424]: RTNETLINK answers: File exists
Aug 10 22:57:45 BC-AlkaliMetal ifup[4424]: Failed to bring up lo.
Aug 10 22:57:45 BC-AlkaliMetal systemd[1]: networking.service: Main process exited, code=exited, status=1/FAILURE
Aug 10 22:57:45 BC-AlkaliMetal systemd[1]: Failed to start Raise network interfaces.
Aug 10 22:57:45 BC-AlkaliMetal systemd[1]: networking.service: Unit entered failed state.
Aug 10 22:57:45 BC-AlkaliMetal systemd[1]: networking.service: Failed with result 'exit-code'.

Thanks to @Rinzwind, this problem can temporary be solved by flushing the lo device:

bytecommander@BC-AlkaliMetal:~$ sudo ip addr flush dev lo
bytecommander@BC-AlkaliMetal:~$ sudo service networking start
bytecommander@BC-AlkaliMetal:~$ systemctl status networking.service 
? networking.service - Raise network interfaces
   Loaded: loaded (/lib/systemd/system/networking.service; enabled; vendor preset: enabled)
  Drop-In: /run/systemd/generator/networking.service.d
           ??50-insserv.conf-$network.conf
   Active: active (exited) since Mi 2016-08-10 22:55:06 CEST; 5s ago
     Docs: man:interfaces(5)
  Process: 9057 ExecStart=/sbin/ifup -a --read-environment (code=exited, status=0/SUCCESS)
  Process: 9052 ExecStartPre=/bin/sh -c [ "$CONFIGURE_INTERFACES" != "no" ] && [ -n "$(ifquery --read-environment --list --exclude=l
 Main PID: 9057 (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/networking.service

Aug 10 22:55:06 BC-AlkaliMetal systemd[1]: Starting Raise network interfaces...
Aug 10 22:55:06 BC-AlkaliMetal systemd[1]: Started Raise network interfaces.

I get the same problem again during the next reboot though.

This is my /etc/network/interfaces config file:

# interfaces(5) file used by ifup(8) and ifdown(8)
iface lo inet static
   address 127.0.0.1
   netmask 255.0.0.0

What is wrong here and how to fix it?

Answer 1

环回接口配置不正确/etc/network/inerfaces：

iface lo inet static
    address 127.0.0.1
    netmask 255.0.0.0

环回接口 ( lo) 被认为是系统的“特殊”接口，因此需要对其进行分类。为了促进这一点，任何对环回接口的引用都应该被删除并替换为默认值：

auto lo
iface lo inet loopback

networking进行此更改后重新启动服务应该允许系统正确抓取它并修复启动时的错误lo。