我刚刚从 17.10 升级到 18.04。更新过程并不顺利。更新提示无法安装“菜单”，然后就被锁定了。我能够从命令行手动恢复更新。
但是现在，重启后 DNS 完全坏了。其他一切（我无能为力）似乎都很好。但是没有 DNS，互联网几乎无法使用。
我的连接状态是：
$ ping www.google.com
ping: www.google.com: Temporary failure in name resolution
$ ifconfig
eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.2.104 netmask 255.255.255.0 broadcast 192.168.2.255
inet6 fe80::8e89:a5ff:fe0f:cec6 prefixlen 64 scopeid 0x20<link>
ether 8c:89:a5:0f:ce:c6 txqueuelen 1000 (Ethernet)
RX packets 87 bytes 37036 (37.0 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 112 bytes 17685 (17.6 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
device interrupt 18
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1000 (Local Loopback)
RX packets 418 bytes 32294 (32.2 KB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 418 bytes 32294 (32.2 KB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:5e:47:cb txqueuelen 1000 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
$ systemctl status resolvconf
● resolvconf.service - Nameserver information manager
Loaded: loaded (/lib/systemd/system/resolvconf.service; enabled; vendor preset: enabled)
Active: active (exited) since Sat 2018-05-26 12:25:31 +08; 1min 9s ago
Docs: man:resolvconf(8)
Process: 3522 ExecStart=/sbin/resolvconf --enable-updates (code=exited, status=0/SUCCESS)
Process: 3521 ExecStartPre=/bin/touch /run/resolvconf/postponed-update (code=exited, status=0/SUCCESS)
Process: 3519 ExecStartPre=/bin/mkdir -p /run/resolvconf/interface (code=exited, status=0/SUCCESS)
Main PID: 3522 (code=exited, status=0/SUCCESS)
$ systemd-resolve --status
Global
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
17.172.in-addr.arpa
18.172.in-addr.arpa
19.172.in-addr.arpa
20.172.in-addr.arpa
21.172.in-addr.arpa
22.172.in-addr.arpa
23.172.in-addr.arpa
24.172.in-addr.arpa
25.172.in-addr.arpa
26.172.in-addr.arpa
27.172.in-addr.arpa
28.172.in-addr.arpa
29.172.in-addr.arpa
30.172.in-addr.arpa
31.172.in-addr.arpa
corp
d.f.ip6.arpa
home
internal
intranet
lan
local
private
test
Link 5 (virbr0-nic)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSSEC setting: allow-downgrade
DNSSEC supported: yes
Link 4 (virbr0)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSSEC setting: allow-downgrade
DNSSEC supported: yes
Link 3 (wlan0)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSSEC setting: allow-downgrade
DNSSEC supported: yes
Link 2 (eth0)
Current Scopes: none
LLMNR setting: yes
MulticastDNS setting: no
DNSSEC setting: allow-downgrade
DNSSEC supported: yes
$ nmcli connection show Wired\ connection\ 1
connection.id: Wired connection 1
connection.uuid: 995000d6-3311-3674-8649-14b6d44af2e3
connection.stable-id: --
connection.interface-name: --
connection.type: 802-3-ethernet
connection.autoconnect: yes
connection.autoconnect-priority: -999
connection.autoconnect-retries: -1 (default)
connection.timestamp: 1527308732
connection.read-only: no
connection.permissions: --
connection.zone: --
connection.master: --
connection.slave-type: --
connection.autoconnect-slaves: -1 (default)
connection.secondaries: --
connection.gateway-ping-timeout: 0
connection.metered: unknown
connection.lldp: -1 (default)
802-3-ethernet.port: --
802-3-ethernet.speed: 0
802-3-ethernet.duplex: --
802-3-ethernet.auto-negotiate: yes
802-3-ethernet.mac-address: 8C:89:A5:0F:CE:C6
802-3-ethernet.cloned-mac-address: --
802-3-ethernet.generate-mac-address-mask:--
802-3-ethernet.mac-address-blacklist: --
802-3-ethernet.mtu: auto
802-3-ethernet.s390-subchannels: --
802-3-ethernet.s390-nettype: --
802-3-ethernet.s390-options: --
802-3-ethernet.wake-on-lan: 1 (default)
802-3-ethernet.wake-on-lan-password: --
ipv4.method: auto
ipv4.dns: --
ipv4.dns-search: --
ipv4.dns-options: (default)
ipv4.dns-priority: 0
ipv4.addresses: --
ipv4.gateway: --
ipv4.routes: --
ipv4.route-metric: -1
ipv4.ignore-auto-routes: no
ipv4.ignore-auto-dns: no
ipv4.dhcp-client-id: --
ipv4.dhcp-timeout: 0
ipv4.dhcp-send-hostname: yes
ipv4.dhcp-hostname: --
ipv4.dhcp-fqdn: --
ipv4.never-default: no
ipv4.may-fail: yes
ipv4.dad-timeout: -1 (default)
ipv6.method: ignore
ipv6.dns: --
ipv6.dns-search: --
ipv6.dns-options: (default)
ipv6.dns-priority: 0
ipv6.addresses: --
ipv6.gateway: --
ipv6.routes: --
ipv6.route-metric: -1
ipv6.ignore-auto-routes: no
ipv6.ignore-auto-dns: no
ipv6.never-default: no
ipv6.may-fail: yes
ipv6.ip6-privacy: 0 (disabled)
ipv6.addr-gen-mode: stable-privacy
ipv6.dhcp-send-hostname: yes
ipv6.dhcp-hostname: --
ipv6.token: --
proxy.method: none
proxy.browser-only: no
proxy.pac-url: --
proxy.pac-script: --
GENERAL.NAME: Wired connection 1
GENERAL.UUID: 995000d6-3311-3674-8649-14b6d44af2e3
GENERAL.DEVICES: eth0
GENERAL.STATE: activated
GENERAL.DEFAULT: yes
GENERAL.DEFAULT6: no
GENERAL.VPN: no
GENERAL.ZONE: --
GENERAL.DBUS-PATH: /org/freedesktop/NetworkManager/ActiveConnection/2
GENERAL.CON-PATH: /org/freedesktop/NetworkManager/Settings/4
GENERAL.SPEC-OBJECT: --
GENERAL.MASTER-PATH: --
IP4.ADDRESS[1]: 192.168.2.104/24
IP4.GATEWAY: 192.168.2.251
IP4.DNS[1]: 192.168.2.251
IP4.DOMAIN[1]: lan
DHCP4.OPTION[1]: requested_subnet_mask = 1
DHCP4.OPTION[2]: requested_rfc3442_classless_static_routes = 1
DHCP4.OPTION[3]: subnet_mask = 255.255.255.0
DHCP4.OPTION[4]: domain_name_servers = 192.168.2.251
DHCP4.OPTION[5]: ip_address = 192.168.2.104
DHCP4.OPTION[6]: requested_static_routes = 1
DHCP4.OPTION[7]: dhcp_server_identifier = 192.168.2.251
DHCP4.OPTION[8]: requested_time_offset = 1
DHCP4.OPTION[9]: broadcast_address = 192.168.2.255
DHCP4.OPTION[10]: requested_interface_mtu = 1
DHCP4.OPTION[11]: dhcp_rebinding_time = 37800
DHCP4.OPTION[12]: requested_domain_name_servers = 1
DHCP4.OPTION[13]: dhcp_message_type = 5
DHCP4.OPTION[14]: requested_broadcast_address = 1
DHCP4.OPTION[15]: routers = 192.168.2.251
DHCP4.OPTION[16]: dhcp_renewal_time = 21600
DHCP4.OPTION[17]: requested_domain_name = 1
DHCP4.OPTION[18]: domain_name = lan
DHCP4.OPTION[19]: requested_routers = 1
DHCP4.OPTION[20]: expiry = 1527351932
DHCP4.OPTION[21]: host_name = steven-ge40
DHCP4.OPTION[22]: requested_netbios_scope = 1
DHCP4.OPTION[23]: requested_wpad = 1
DHCP4.OPTION[24]: requested_ms_classless_static_routes = 1
DHCP4.OPTION[25]: requested_netbios_name_servers = 1
DHCP4.OPTION[26]: network_number = 192.168.2.0
DHCP4.OPTION[27]: requested_domain_search = 1
DHCP4.OPTION[28]: next_server = 192.168.2.251
DHCP4.OPTION[29]: requested_ntp_servers = 1
DHCP4.OPTION[30]: requested_host_name = 1
DHCP4.OPTION[31]: dhcp_lease_time = 43200
IP6.ADDRESS[1]: fe80::8e89:a5ff:fe0f:cec6/64
IP6.GATEWAY: --
$ cat /etc/systemd/resolved.conf
# This file is part of systemd.
#
# systemd is free software; you can redistribute it and/or modify it
# under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 2.1 of the License, or
# (at your option) any later version.
#
# Entries in this file show the compile time defaults.
# You can change settings by editing this file.
# Defaults can be restored by simply deleting this file.
#
# See resolved.conf(5) for details
[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
DNSSEC=allow-downgrade
#Cache=yes
#DNSStubListener=yes
$ cat /run/systemd/resolve/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients directly to
# all known uplink DNS servers. This file lists all configured search domains.
#
# Third party programs must not access this file directly, but only through the
# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
# replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.
# No DNS servers known.
$ cat /run/resolvconf/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.
$ ls -al /etc/resolv.conf
lrwxrwxrwx 1 root root 29 Mar 30 2015 /etc/resolv.conf -> ../run/resolvconf/resolv.conf
$ cat /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
# 127.0.0.53 is the systemd-resolved stub resolver.
# run "systemd-resolve --status" to see details about the actual nameservers.
知道是什么原因造成的吗？我怀疑这与 /etc/resolv.conf 没有指向 systemd resolvd 有关，但 systemd resolvd 似乎也对 DNS 服务器一无所知。然而，网络管理器显示它已成功获取它们，并且 IT 部门知道它们。
我还可以尝试什么？
systemd resolve 对我来说似乎完全坏了。所以我卸载了它并安装了 unbound。第一次就成功了，没有引起任何问题。