当我启动 Ubuntu 服务器时，DNS 解析不起作用。您可以通过查看 resolv.conf 轻松发现此问题：
~ # 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.
然后我启用已解析的服务：
~ # systemctl enable systemd-resolved.service
事情正如预期的那样：
~ # 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.
nameserver 127.0.0.53
配置
- Ubuntu 19.04
- 5.0.0-23-通用
安装的相关软件包：
~ # cat /etc/resodpkg -l |grep systemd
ii libnss-resolve:amd64 240-6ubuntu5.2 amd64 nss module to resolve names via systemd-resolved
ii libnss-systemd:amd64 240-6ubuntu5.2 amd64 nss module providing dynamic user and group name resolution
ii libpam-systemd:amd64 240-6ubuntu5.2 amd64 system and service manager - PAM module
ii libsystemd0:amd64 240-6ubuntu5.2 amd64 systemd utility library
ii networkd-dispatcher 2.0-2 all Dispatcher service for systemd-networkd connection status changes
ii python3-systemd 234-2build2 amd64 Python 3 bindings for systemd
ii systemd 240-6ubuntu5.2 amd64 system and service manager
ii systemd-sysv 240-6ubuntu5.2 amd64 system and service manager - SysV links
~ # dpkg -l |grepdpkg -l |grep resolv
ii libc-ares2:amd64 1.14.0-1 amd64 asynchronous name resolver
ii libgeoip1:amd64 1.6.12-1 amd64 non-DNS IP-to-country resolver library
ii libnss-resolve:amd64 240-6ubuntu5.2 amd64 nss module to resolve names via systemd-resolved
ii resolvconf 1.79ubuntu13 all name server information handler
更新至 19.04 之前，名称解析在启动时有效。
系统日志中没有明显错误。相关摘录：
Aug 3 11:41:16 green systemd[1]: Starting Network Name Resolution...
Aug 3 11:41:16 green systemd-resolved[807]: Positive Trust Anchors:
Aug 3 11:41:16 green systemd-resolved[807]: . IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5
Aug 3 11:41:16 green systemd-resolved[807]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Aug 3 11:41:16 green systemd-resolved[807]: Negative trust anchors: 10.in-addr.arpa 16.172.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.arp
Aug 3 11:41:16 green systemd[1]: Started Network Name Resolution.
重启前的状态（名称服务器列在 /etc/resolv.conf 中）：
~ # systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
Active: active (running) since Sat 2019-08-03 11:39:32 EDT; 2 days ago
Docs: man:systemd-resolved.service(8)
https://www.freedesktop.org/wiki/Software/systemd/resolved
https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
Main PID: 807 (systemd-resolve)
Status: "Processing requests..."
Tasks: 1 (limit: 4915)
Memory: 7.9M
CGroup: /system.slice/systemd-resolved.service
└─807 /lib/systemd/systemd-resolved
Aug 06 10:00:38 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:04:06 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:04:06 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:04:06 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:04:06 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:15:53 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:17:05 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:17:05 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:17:05 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:17:05 green systemd-resolved[807]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
重启前的状态（/etc/resolv.conf 中没有列出任何内容）：
~ # systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2019-08-06 10:23:53 EDT; 1min 9s ago
Docs: man:systemd-resolved.service(8)
https://www.freedesktop.org/wiki/Software/systemd/resolved
https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
Main PID: 798 (systemd-resolve)
Status: "Processing requests..."
Tasks: 1 (limit: 4915)
Memory: 7.8M
CGroup: /system.slice/systemd-resolved.service
└─798 /lib/systemd/systemd-resolved
Aug 06 10:23:51 green systemd[1]: Starting Network Name Resolution...
Aug 06 10:23:52 green systemd-resolved[798]: Positive Trust Anchors:
Aug 06 10:23:52 green systemd-resolved[798]: . IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5
Aug 06 10:23:52 green systemd-resolved[798]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Aug 06 10:23:52 green systemd-resolved[798]: Negative trust anchors: 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.
Aug 06 10:23:52 green systemd-resolved[798]: Using system hostname 'green'.
Aug 06 10:23:53 green systemd[1]: Started Network Name Resolution.
~ # systemd-resolve --status
Global
LLMNR setting: no
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 8.8.8.8
DNS Servers: 8.8.8.8
8.8.4.4
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 3 (eno2)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 2 (eno1)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
之后systemctl enable systemd-resolved.service（名称服务器列在 /etc/resolv.conf 中）：
~ # systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enabled)
Active: active (running) since Tue 2019-08-06 10:23:53 EDT; 3min 47s ago
Docs: man:systemd-resolved.service(8)
https://www.freedesktop.org/wiki/Software/systemd/resolved
https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-managers
https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
Main PID: 798 (systemd-resolve)
Status: "Processing requests..."
Tasks: 1 (limit: 4915)
Memory: 7.9M
CGroup: /system.slice/systemd-resolved.service
└─798 /lib/systemd/systemd-resolved
Aug 06 10:23:52 green systemd-resolved[798]: Positive Trust Anchors:
Aug 06 10:23:52 green systemd-resolved[798]: . IN DS 19036 8 2 49aac11d7b6f6446702e54a1607371607a1a41855200fd2ce1cdde32f24e8fb5
Aug 06 10:23:52 green systemd-resolved[798]: . IN DS 20326 8 2 e06d44b80b8f1d39a95c0b0d7c65d08458e880409bbc683457104237c7f8ec8d
Aug 06 10:23:52 green systemd-resolved[798]: Negative trust anchors: 10.in-addr.arpa 16.172.in-addr.arpa 17.172.in-addr.arpa 18.172.in-addr.arpa 19.172.in-addr.arpa 20.
Aug 06 10:23:52 green systemd-resolved[798]: Using system hostname 'green'.
Aug 06 10:23:53 green systemd[1]: Started Network Name Resolution.
Aug 06 10:27:32 green systemd-resolved[798]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:27:35 green systemd-resolved[798]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:27:35 green systemd-resolved[798]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
Aug 06 10:27:35 green systemd-resolved[798]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature
systemd-resolve --status显示与之前相同。
答案1
您安装了类似 resolvconf 的东西，它通过注释掉 stub-resolv.conf 中 /etc/resolv.conf 应该链接到的 53 个监听地址，完全切断了 sytemd-resolved。对于全新安装的 Ubuntu 18.04，我需要的唯一附加名称解析包是 libnss-resolve。我从不使用 resolvconf，所以不知道你为什么需要它。