总结
我遇到了一种奇怪的情况，我可以在某些主机上进行 DNS 查找，但不能在其他主机上进行。这似乎与 resolv.conf 有关，其中一个名称服务器条目指向我的名称服务器，另一个可能与 docker 有关，但我不知道如何修复它。
问题
我一直在读Stéphane Graber 对 LXD 的精彩介绍并想尝试一下。因此，我做了：
$ sudo usermod -a -G lxd <myusername>
$ newgrp lxd
$ sudo lxd init
我使用全部默认设置进行配置。然后我输入：
$ lxc image list images:
error: Get https://images.linuxcontainers.org/streams/v1/index.json: lookup images.linuxcontainers.org: no such host
一些测试
我尝试在另一台电脑上通过 Web 浏览器访问该地址，一切正常。因此，我认为 DNS 设置一定存在问题，但是：
$ host images.linuxcontainers.org
images.linuxcontainers.org is an alias for canonical.images.linuxcontainers.org.
canonical.images.linuxcontainers.org has address 91.189.91.21
canonical.images.linuxcontainers.org has address 91.189.88.37
canonical.images.linuxcontainers.org has IPv6 address 2001:67c:1560:8001::21
canonical.images.linuxcontainers.org has IPv6 address 2001:67c:1562::41
因此我尝试了 wget：
$ wget https://images.linuxcontainers.org/streams/v1/index.json
--2016-11-10 15:56:22-- https://images.linuxcontainers.org/streams/v1/index.json
Resolving images.linuxcontainers.org (images.linuxcontainers.org)... failed: Name or service not known.
wget: unable to resolve host address "images.linuxcontainers.org"
这让我认为我的互联网连接有问题，但如果我使用 us.images.linuxcontainers.org（我在网上某处看到提到过）：
$ wget https://us.images.linuxcontainers.org/streams/v1/index.json
--2016-11-10 15:57:26-- https://us.images.linuxcontainers.org/streams/v1/index.json
Resolving us.images.linuxcontainers.org (us.images.linuxcontainers.org)... 91.189.91.21, 2001:67c:1562::41
Connecting to us.images.linuxcontainers.org (us.images.linuxcontainers.org)|91.189.91.21|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 3086 (3.0K) [application/json]
Saving to: "index.json"
index.json 100%[==================================================================================>] 3.01K --.-KB/s in 0s
2016-11-10 15:57:26 (8.36 MB/s) - "index.json" saved [3086/3086]
我还尝试了 canonical.images.linuxcontainers.org，根据host上文，它是 images.linuxcontainers.org 的别名，并且也有效，因此看起来host可以查找 images.linuxcontainers.org，而wget和lxc不能，但 wget 能访问 canonical.images.linuxcontainers.org 和我尝试过的大多数其他网站。
$ wget https://canonical.images.linuxcontainers.org/streams/v1/index.json
--2016-11-10 16:02:28-- https://canonical.images.linuxcontainers.org/streams/v1/index.json
Resolving canonical.images.linuxcontainers.org (canonical.images.linuxcontainers.org)... 91.189.91.21, 91.189.88.37
Connecting to canonical.images.linuxcontainers.org (canonical.images.linuxcontainers.org)|91.189.91.21|:443... connected.
ERROR: no certificate subject alternative name matches
requested host name "canonical.images.linuxcontainers.org".
To connect to canonical.images.linuxcontainers.org insecurely, use `--no-check-certificate'.
$ wget --no-check-certificate https://canonical.images.linuxcontainers.org/streams/v1/index.json
--2016-11-10 16:02:37-- https://canonical.images.linuxcontainers.org/streams/v1/index.json
Resolving canonical.images.linuxcontainers.org (canonical.images.linuxcontainers.org)... 91.189.88.37, 91.189.91.21
Connecting to canonical.images.linuxcontainers.org (canonical.images.linuxcontainers.org)|91.189.88.37|:443... connected.
WARNING: no certificate subject alternative name matches
requested host name "canonical.images.linuxcontainers.org".
HTTP request sent, awaiting response... 301 Moved Permanently
Location: https://uk.images.linuxcontainers.org/streams/v1/index.json [following]
--2016-11-10 16:02:37-- https://uk.images.linuxcontainers.org/streams/v1/index.json
Resolving uk.images.linuxcontainers.org (uk.images.linuxcontainers.org)... 91.189.88.37, 2001:67c:1560:8001::21
Connecting to uk.images.linuxcontainers.org (uk.images.linuxcontainers.org)|91.189.88.37|:443... connected.
HTTP request sent, awaiting response... 200 OK
Length: 3086 (3.0K) [application/json]
Saving to: "index.json.1"
index.json.1 100%[==================================================================================>] 3.01K --.-KB/s in 0s
2016-11-10 16:02:38 (96.5 MB/s) - "index.json.1" saved [3086/3086]
我也尝试过wget -4排除wget -6IPv6 问题，但结果都一样。最后我尝试了一些其他类似的程序，w3m但也没有区别。
我显然遗漏了一些东西；有人能提供一些建议，说明为什么我无法lxc下载图像列表吗？
个人电脑
该 PC 相对较新，运行 Ubuntu Server 16.10，很少有额外的包安装在主主机上。Docker 已安装并正在运行，但没有启动任何容器。有趣的是，我最近重新启动到内核 4.8.6 来测试我遇到的另一个问题，使用该内核我可以访问 images.linuxcontainers.org，但 docker 无法启动，所以我想知道这是否与 docker 有关。
配置
/etc/resolv.conf看起来像这样（但由于某些我不知道的原因，实际上是一个符号链接/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
nameserver 192.168.1.254
nameserver 127.0.0.53
search lan
如果我查询第一个列出的名称服务器，我会得到与不附加名称服务器地址相同的结果：
$ host images.linuxcontainers.org 192.168.1.254
images.linuxcontainers.org is an alias for canonical.images.linuxcontainers.org.
canonical.images.linuxcontainers.org has address 91.189.91.21
canonical.images.linuxcontainers.org has address 91.189.88.37
canonical.images.linuxcontainers.org has IPv6 address 2001:67c:1560:8001::21
canonical.images.linuxcontainers.org has IPv6 address 2001:67c:1562::41
如果我查询第二个，它会超时而无法到达服务器：
$ host images.linuxcontainers.org 127.0.0.53
;; connection timed out; no servers could be reached
如果我查询第二个但使用规范名称，它会起作用然后超时？？？
$ host canonical.images.linuxcontainers.org 127.0.0.53
Using domain server:
Name: 127.0.0.53
Address: 127.0.0.53#53
Aliases:
canonical.images.linuxcontainers.org has address 91.189.88.37
canonical.images.linuxcontainers.org has address 91.189.91.21
;; connection timed out; no servers could be reached
;; connection timed out; no servers could be reached
编辑1：
/etc/nsswitch.conf看起来像这样：
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.
passwd: compat
group: compat
shadow: compat
gshadow: files
hosts: files resolve [!UNAVAIL=return] dns
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
netgroup: nis
编辑2
修改后的 nsswitch.conf 现在如下所示：
# /etc/nsswitch.conf
#
# Example configuration of GNU Name Service Switch functionality.
# If you have the `glibc-doc-reference' and `info' packages installed, try:
# `info libc "Name Service Switch"' for information about this file.
passwd: compat
group: compat
shadow: compat
gshadow: files
hosts: files resolve dns
networks: files
protocols: db files
services: db files
ethers: db files
rpc: db files
netgroup: nis
编辑3
/etc/systemd/resolved.conf 的内容：
# 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=8.8.8.8 8.8.4.4 2001:4860:4860::8888 2001:4860:4860::8844
#Domains=
#LLMNR=yes
#DNSSEC=no
#Cache=yes
答案1
这是第一次看到
resolvehosts 关键字，看起来不对。你应该有类似的东西hosts: files dns [NOTFOUND=return]或者如果你已经安装了 mDNS
hosts: files dns mdns4_minimal [NOTFOUND=return] mdns4您可以删除
[NOTFOUND=return]或[!UNAVAIL=return]，如果没有剩余内容可查询，它就是默认操作。好吧，经过一番挖掘，我发现有一个对我来说很新的 NSS 模块
libnss-resolvenss module to resolve names via systemd-resolved nss-resolve is a plugin for the GNU Name Service Switch (NSS) functionality of the GNU C Library (glibc) providing DNS and LLMNR resolution to programs via the systemd-resolved daemon (provided in the systemd package). Installing this package automatically adds resolve to /etc/nsswitch.conf.您可能最终会以某种方式安装它，而不是使用您提到的软件包。没有软件包依赖于它。
~$ apt-cache rdepends libnss-resolve libnss-resolve Reverse Depends:但我现在不能说什么，为什么
systemd-resolved不可靠。最好将其报告为 bugsystemd。