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：
Jobfornginx.service failed because the controlprocessexitedwitherrorcode. See"systemctl status nginx.service"and"journalctl -xe"fordetails.invoke-rc.d: initscript nginx, action"start"failed.dpkg:errorprocessingpackagenginx-core (--configure):subprocess installed post-installation script returnederrorexitstatus1dpkg: dependency problems preventconfigurationofnginx: nginx dependsonnginx-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:Packagenginx-coreisnotconfigured yet.Packagenginx-fullisnotinstalled.Packagenginx-lightisnotinstalled.Packagenginx-extrasisnotinstalled. nginx dependsonnginx-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:Packagenginx-coreisnotconfigured yet. No apportreportwritten because theerrormessage indicates its a followuperrorfrom a previousfailure.Packagenginx-fullisnotinstalled.Packagenginx-lightisnotinstalled.Packagenginx-extrasisnotinstalled.dpkg:errorprocessingpackagenginx (--configure):dependency problems - leaving unconfiguredProcessing triggersforlibc-bin (2.23-0ubuntu9) ...Errors were encounteredwhileprocessing: nginx-core nginxE: Sub-process/usr/bin/dpkg returned anerrorcode (1)
查看nginx.service状态
$ systemctl status nginx.service
● nginx.service - A high performance web serverandareverse proxy server Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled) Active: failed (Result: exit-code) since Sat2018-03-1723:16:40CST;1min18s ago Process:26795ExecStartPre=/usr/sbin/nginx -t -q -g daemonon;master_processon; (code=exited,status=1/FAILURE) Main PID:18259(code=exited, status=0/SUCCESS)Mar1723:16:40VM-0-5-ubuntu systemd[1]: Starting A high performance web serverandareverse proxy server...Mar1723:16:40VM-0-5-ubuntu nginx[26795]: nginx: [emerg]open()"/etc/nginx/nginx.conf"failed (2: No suchfileordireMar1723:16:40VM-0-5-ubuntu nginx[26795]: nginx: configurationfile/etc/nginx/nginx.conf test failedMar1723:16:40VM-0-5-ubuntu systemd[1]: nginx.service: Controlprocessexited, code=exited status=1Mar1723:16:40VM-0-5-ubuntu systemd[1]: FailedtostartA high performance web serverandareverse proxy server.Mar1723:16:40VM-0-5-ubuntu systemd[1]: nginx.service: Unit entered failed state.Mar1723:16:40VM-0-5-ubuntu systemd[1]: nginx.service: Failedwithresult'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 nametcp000.0.0.0:220.0.0.0:* LISTEN1287/sshdudp000.0.0.0:680.0.0.0:*891/dhclientudp00172.21.0.5:1230.0.0.0:*1231/ntpdudp00127.0.0.1:1230.0.0.0:*1231/ntpdudp000.0.0.0:1230.0.0.0:*1231/ntpdudp600:::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 nginxReading package lists... DoneBuilding dependency treeReading state information... DoneThe 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-coreUse'sudo apt autoremove'toremove them.Thefollowingpackages will be REMOVED: nginx*0upgraded,0newly installed,1toremoveand205notupgraded.2notfully installedorremoved.Afterthis operation,37.9kB diskspacewill be freed.Doyou wanttocontinue? [Y/n] y(Readingdatabase...66386filesanddirectories currently installed.)Removing nginx (1.10.3-0ubuntu0.16.04.2) ...Setting up nginx-core (1.10.3-0ubuntu0.16.04.2) ...Jobfornginx.servicefailedbecause the control process exitedwitherrorcode. See"systemctl status nginx.service"and"journalctl -xe"fordetails.invoke-rc.d: initscript nginx,action"start"failed.dpkg:errorprocessingpackagenginx-core (--configure):subprocess installed post-installation script returnederrorexitstatus1Errorswere encounteredwhileprocessing: nginx-coreE: Sub-process /usr/bin/dpkg returned anerrorcode (1)
卸载自动安装且不再需要的依赖包
$ sudo apt-get autoremoveReading package lists... DoneBuilding dependency treeReading state information... DoneThe following packages will be REMOVED: fontconfig-config fonts-dejavu-core libfontconfig1 libgd3 libjbig0 libjpeg-turbo8 libjpeg8 libtiff5 libvpx3 libxpm4 libxslt1.1nginx-commonnginx-core0upgraded,0newly installed,13to removeand205notupgraded.1notfully installedorremoved.After this operation,9,745kB disk space will be freed.Doyou want to continue? [Y/n] y(Reading database ...66383filesanddirectories 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 |grepnginxnginx-common deinstall
卸载nginx-common不保留配置文件
$ sudo apt-get--purge remove nginx-commonReading package lists... DoneBuilding dependency treeReading state information... DoneThe following packages will be REMOVED: nginx-common*0upgraded,0newly installed,1toremoveand205notupgraded.After this operation,0Bofadditional diskspacewill be used.Do you wanttocontinue? [Y/n] y(Reading database ...66243filesanddirectoriescurrently installed.)Removing nginx-common (1.10.3-0ubuntu0.16.04.2) ...Purging configurationfilesfornginx-common (1.10.3-0ubuntu0.16.04.2) ...dpkg: warning:whileremoving nginx-common,directory'/var/www/html'notemptysonotremoved
重新安装nginx
$ sudo apt-getinstall nginx...
查看版本号，执行nginx配置文件语法检测
$ nginx -vnginxversion: nginx/1.10.3(Ubuntu)$ sudo nginx -tnginx: the configurationfile/etc/nginx/nginx.confsyntaxisoknginx: configurationfile/etc/nginx/nginx.conftestissuccessful
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-getremove nginx-common...# 卸载nginx-common，nginx配置文件已经被删除（包括但不限于）$ sudo apt-getremove--purge nginx-common$ find /etc/nginx/find: ‘/etc/nginx/’: No suchfileordirectory
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 nginxnginx-commondeinstall
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-getremove --purge nginx$ sudo apt-getautoremove --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-getremove nginx$ sudo apt-getautoremove$ sudo apt update$ sudo apt-getinstall nginx# 安装软件包# sudo apt-get install 软件包名称`# eg: $ sudo apt-getinstall nginx# 卸载软件包# sudo apt-get remove 软件包名称# eg: $ sudo apt-getremove 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-getremove --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”?
