原文链接：https://segmentfault.com/a/1190000014027697
起因
之前在网上看文章提到说，通过apt-get的方式安装nginx，可能安装不是最新版本的情况，考虑到在Ubuntu下第一次安装nginx，以后肯定会有卸载重新安装新版本的需求，刚好刚开始学习nginx，索性练习下卸载重装的过程。
安装
使用Ubuntu下的包管理工具apt来安装nginx
$ sudo apt-get install nginx
卸载
同样使用apt来卸载nginx
$ sudo apt-get remove nginx
sudo apt-get autoremove命令帮我们卸载不再需要的依赖包
在这里我们卸载nginx相关的依赖包
$ sudo apt-get autoremove
删除nginx配置文件夹
$ sudo rm -rf /etc/nginx
重新安装nginx
# 更新源
$ sudo apt update
$ sudo apt-get install nginx
然而控制台报错：
Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details.
invoke-rc.d: initscript nginx, action "start" failed.
dpkg: error processing package nginx-core (--configure):
subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of nginx:
nginx depends on nginx-core (>= 1.10.3-0ubuntu0.16.04.2) | nginx-full (>= 1.10.3-0ubuntu0.16.04.2) | nginx-light (>= 1.10.3-0ubuntu0.16.04.2) | nginx-extras (>= 1.10.3-0ubuntu0.16.04.2); however:
Package nginx-core is not configured yet.
Package nginx-full is not installed.
Package nginx-light is not installed.
Package nginx-extras is not installed.
nginx depends on nginx-core (<< 1.10.3-0ubuntu0.16.04.2.1~) | nginx-full (<< 1.10.3-0ubuntu0.16.04.2.1~) | nginx-light (<< 1.10.3-0ubuntu0.16.04.2.1~) | nginx-extras (<< 1.10.3-0ubuntu0.16.04.2.1~); however:
Package nginx-core is not configured yet.
No apport report written because the error message indicates its a followup error from a previous failure.
Package nginx-full is not installed.
Package nginx-light is not installed.
Package nginx-extras is not installed.
dpkg: error processing package nginx (--configure):
dependency problems - leaving unconfigured
Processing triggers for libc-bin (2.23-0ubuntu9) ...
Errors were encountered while processing:
nginx-core
nginx
E: Sub-process /usr/bin/dpkg returned an error code (1)
查看nginx.service状态
$ systemctl status nginx.service
● nginx.service - A high performance web server and a reverse proxy server
Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Sat 2018-03-17 23:16:40 CST; 1min 18s ago
Process: 26795 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=1/FAILURE)
Main PID: 18259 (code=exited, status=0/SUCCESS)
Mar 17 23:16:40 VM-0-5-ubuntu systemd[1]: Starting A high performance web server and a reverse proxy server...
Mar 17 23:16:40 VM-0-5-ubuntu nginx[26795]: nginx: [emerg] open() "/etc/nginx/nginx.conf" failed (2: No such file or direMar 17 23:16:40 VM-0-5-ubuntu nginx[26795]: nginx: configuration file /etc/nginx/nginx.conf test failed
Mar 17 23:16:40 VM-0-5-ubuntu systemd[1]: nginx.service: Control process exited, code=exited status=1
Mar 17 23:16:40 VM-0-5-ubuntu systemd[1]: Failed to start A high performance web server and a reverse proxy server.
Mar 17 23:16:40 VM-0-5-ubuntu systemd[1]: nginx.service: Unit entered failed state.
Mar 17 23:16:40 VM-0-5-ubuntu systemd[1]: nginx.service: Failed with result 'exit-code'.
仔细看报错信息，获取到两个信息点：
- Package nginx-core is not configured yet.
- Package nginx-full/nginx-light/nginx-extras is not installed.
于是上网搜，网上找说可能是apache占用了80端口导致报错
查看端口占用情况
$ sudo netstat -nlp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 1287/sshd
udp 0 0 0.0.0.0:68 0.0.0.0:* 891/dhclient
udp 0 0 172.21.0.5:123 0.0.0.0:* 1231/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:* 1231/ntpd
udp 0 0 0.0.0.0:123 0.0.0.0:* 1231/ntpd
udp6 0 0 :::123 :::* 1231/ntpd
发现80端口没被占用，而且systemctl status nginx.service的提示信息也没提及80端口被占用，如果提示信息中说80端口被占用，可以执行以下两步试试：
终止apache运行
$ sudo service apache2 stop
重新安装nginx
$ sudo apt-get install nginx
了解详细信息请看askubuntu上的提问
上述情况与我的并不相符，于是换个思路，报错信息中提及nginx的配置文件不存在，思考为什么卸载重装nginx，却没有生成配置文件？
和第一次安装的时候不一样，然后百度上搜nginx卸载重装后配置文件没有重新生成，找到了类似的问题，给出了如下的操纵步骤：
卸载nginx不保留配置文件
$ sudo apt-get --purge remove nginx
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
fontconfig-config fonts-dejavu-core libfontconfig1 libgd3 libjbig0 libjpeg-turbo8 libjpeg8 libtiff5 libvpx3 libxpm4
libxslt1.1 nginx-common nginx-core
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
nginx*
0 upgraded, 0 newly installed, 1 to remove and 205 not upgraded.
2 not fully installed or removed.
After this operation, 37.9 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 66386 files and directories currently installed.)
Removing nginx (1.10.3-0ubuntu0.16.04.2) ...
Setting up nginx-core (1.10.3-0ubuntu0.16.04.2) ...
Job for nginx.service failed because the control process exited with error code. See "systemctl status nginx.service" and "journalctl -xe" for details.
invoke-rc.d: initscript nginx, action "start" failed.
dpkg: error processing package nginx-core (--configure):
subprocess installed post-installation script returned error exit status 1
Errors were encountered while processing:
nginx-core
E: Sub-process /usr/bin/dpkg returned an error code (1)
卸载自动安装且不再需要的依赖包
$ sudo apt-get autoremove
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
fontconfig-config fonts-dejavu-core libfontconfig1 libgd3 libjbig0 libjpeg-turbo8 libjpeg8 libtiff5 libvpx3 libxpm4
libxslt1.1 nginx-common nginx-core
0 upgraded, 0 newly installed, 13 to remove and 205 not upgraded.
1 not fully installed or removed.
After this operation, 9,745 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 66383 files and directories currently installed.)
Removing nginx-core (1.10.3-0ubuntu0.16.04.2) ...
Removing libgd3:amd64 (2.1.1-4ubuntu0.16.04.8) ...
Removing libfontconfig1:amd64 (2.11.94-0ubuntu1.1) ...
Removing fontconfig-config (2.11.94-0ubuntu1.1) ...
Removing fonts-dejavu-core (2.35-1) ...
Removing libtiff5:amd64 (4.0.6-1ubuntu0.2) ...
Removing libjbig0:amd64 (2.1-3.1) ...
Removing libjpeg8:amd64 (8c-2ubuntu8) ...
Removing libjpeg-turbo8:amd64 (1.4.2-0ubuntu3) ...
Removing libvpx3:amd64 (1.5.0-2ubuntu1) ...
Removing libxpm4:amd64 (1:3.5.11-1ubuntu0.16.04.1) ...
Removing libxslt1.1:amd64 (1.1.28-2.1ubuntu0.1) ...
Removing nginx-common (1.10.3-0ubuntu0.16.04.2) ...
Processing triggers for libc-bin (2.23-0ubuntu9) ...
Processing triggers for man-db (2.7.5-1) ...
筛选已安装软件包中与nginx有关的
$ dpkg --get-selections | grep nginx
nginx-common deinstall
卸载nginx-common不保留配置文件
$ sudo apt-get --purge remove nginx-common
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
nginx-common*
0 upgraded, 0 newly installed, 1 to remove and 205 not upgraded.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
(Reading database ... 66243 files and directories currently installed.)
Removing nginx-common (1.10.3-0ubuntu0.16.04.2) ...
Purging configuration files for nginx-common (1.10.3-0ubuntu0.16.04.2) ...
dpkg: warning: while removing nginx-common, directory '/var/www/html' not empty so not removed
重新安装nginx
$ sudo apt-get install nginx
...
查看版本号，执行nginx配置文件语法检测
$ nginx -v
nginx version: nginx/1.10.3 (Ubuntu)
$ sudo nginx -t
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful
虽然nginx已经重装好了，但是一路下来还有几个困惑：
- apt-get autoremove到底是按什么规则卸载软件？
- 为什么nginx-common没有在一开始的时候卸载？
1. apt-get autoremove到底是按什么规则卸载软件？
apt-get autoremove：删除，自动安装的，且不再需要的
（不被其他软件当作依赖的）软件包
举个栗子: 通过apt-get方式安装nginx时，会通过引导自动安装所需的依赖包（nginx-core），而当我们卸载nginx后，
那些自动安装的依赖包就成为不再需要的软件包（nginx-core），通过apt-get autoremove会自动清理它们
既然会自动删除不再需要的软件包，那么为什么nginx-common没被删除？
2. 为什么nginx-common没有在apt-get autoremove的时候卸载？
不知道细心的童鞋发现没，我们在卸载nginx的时候，
手动删除了nginx的配置文件夹（sudo rm -rf /etc/nginx）。
那这些配置文件夹和nginx-common软件包有什么关系呢？
通过查找ubuntu packages，找到了Ubuntu16.0.4下nginx-common软件包的文件清单。
按照清单上的目录手动排查，发现本机上除了手动删除的/etc/nginx目录不存在，文件清单内的其他文件都没有被删除，
猜测可能是nginx-common软件包完整性被破坏，导致autoremove的时候没有被删除，当然这只我的猜测。
问题回答后续补充:
整理完全卸载nginx命令时，发现执行如下命令，ngnix的配置文件并没有被删除
$ sudo apt-get remove --purge nginx
查阅ubuntu packages发现，nginx依赖nginx-core，nginx-core依赖nginx-common，且其中nginx的配置文件属于nginx-common软件包配置文件的一部分。
执行如下命令进一步验证
# 卸载nginx-common ，nginx配置文件不会被删除
$ sudo apt-get remove nginx-common
...
# 卸载nginx-common，nginx配置文件已经被删除（包括但不限于）
$ sudo apt-get remove --purge nginx-common
$ find /etc/nginx/
find: ‘/etc/nginx/’: No such file or directory
推翻之前的猜测：
apt-get autoremove执行时，nginx-common软件包已经被选择用于卸载( deinstall )，但是实际还没有卸载。
$ dpkg --get-selections| grep nginx
nginx-common deinstall
了解更多关于deinstall，点击这里，如果有知道为什么的同学请不吝赐教。
命令汇总
# 完全卸载nginx
$ sudo apt-get remove --purge nginx
$ sudo apt-get autoremove --purge
# 更新nginx，保留配置文件
# 亲测nginx.conf不会被删除和覆盖，但保险起见还是建议先备份
$ sudo apt-get remove nginx
$ sudo apt-get autoremove
$ sudo apt update
$ sudo apt-get install nginx
# 安装软件包
# sudo apt-get install 软件包名称`
# eg:
$ sudo apt-get install nginx
# 卸载软件包
# sudo apt-get remove 软件包名称
# eg:
$ sudo apt-get remove nginx
# 卸载软件包且不保留配置文件
# sudo apt-get remove --purge 软件包名称
# eg:
$ sudo apt-get remove --purge nginx
# 卸载自动安装的软件包且不保留配置文件
# sudo apt-get autoremove --purge
# 列出本地软件包列表
# dpkg --get-selections [| grep 筛选关键字]
# eg:（列出本地所有软件包）
$ dpkg --get-selections
# eg:（列出本地与ngnix有关的软件包）
$ dpkg --get-selections | grep nginx
# 查看进程信息
# ps -ef [| grep 筛选关键字]
# eg:（列出所有进程信息）
$ ps -ef
# eg:（列出与nginx有关的进程信息）
$ ps -ef | grep nginx
# 查看端口占用信息
$ sudo netstat -nlp
参考链接汇总
Package nginx-core not configured yet.Sub-process :/user/bin/dpkg returned an error code(1)
nginx fail to install on Ubuntu 15.10 server
Ubuntu 14.04上卸载nginx之后重新安装没有重新生成配置文件的解决方法
在 xenial 发行版中 all 硬件架构下的 nginx-common 软件包文件清单
What is difference between the options “autoclean”, “autoremove” and “clean”?
dpkg --get-selections shows packages marked “deinstall”