最近在学习postgresql，于是打算在电脑上把数据库装上。看了网上的教程，突出一个字简单。然而，我却遇到许多莫名其妙的问题。
具体步骤就不说了。
安装
创建文件 /etc/apt/sources.list.d/pgdg.list，根据系统版本添加下面这行
#14.04
deb http://apt.postgresql.org/pub/repos/apt/ trusty-pgdg main
#16.04
deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main
#17.04
deb http://apt.postgresql.org/pub/repos/apt/ zesty-pgdg main
这样能获得最新版本的postgresql，如果要安装其他版本
sudo apt install postgresql-xxx
2.安装完之后，直接输入psql，会显示以下错误
psql: could not connect to server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?
服务没有开启，输入命令：
#xx替换为版本号
sudo systemctl start postgresql@xx-main.service
安装有多版本的话
#切换到postgres用户
sudo su postgres
#列出所有分支
pg_lsclusters
问题
接下来就是我遇到的坑了
1.ubuntu dpkg: error processing package postgresql-common (–configure)….
具体错误一大堆：
dpkg: error processing package postgresql-common (--configure):
subprocess installed post-installation script returned error exit status 127
dpkg: dependency problems prevent configuration of postgresql-9.3:
postgresql-9.3 depends on postgresql-common (>= 142~); however:
Package postgresql-common is not configured yet.
dpkg: error processing package postgresql-9.3 (--configure):
dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of postgresql:
postgresql depends on postgresql-9.3; however:
Package postgresql-9.3 is not configured yet.
dpkg: error processing package postgresql (--configure):
dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
No apport report written because the error message indicates its a followup error from a previous failure.
Processing triggers for ureadahead (0.100.0-16) ...
Errors were encountered while processing:
postgresql-common
postgresql-9.3
postgresql
E: Sub-process /usr/bin/dpkg returned an error code (1)
然而主要错误就是，postgresql-common安装失败。如果你已经尝试了网上所有解决方案都没有解决，可以尝试下面这种：
备份/var/lib/dpkg/status文件
sudo cp /var/lib/dpkg/status /var/lib/dpkg/status.bak
然后打开文件该文件，查找postgresql-common
Package: postgresql-common
#关键就在这里
Status: install ok half-configured
Priority: optional
Section: database
注意到报错是 not configured yet，于是我尝试将状态改为 install ok installed (参照了其他正常安装的包）。安装成功，关于这些状态区别可以去查看其他资料。
2.关于psql: could not connect to server:
No such file or directory Is the server running locally and accepting connections on Unix domain socket “/var/run/postgresql/.s.PGSQL.5432”?
这个错误比较隐蔽，我是通过查看日志解决的。一般服务开启，端口没有被占用，数据都能正常连接。但是，我始终没法连接数据库，查看日志发现错误是无法转换localhost。我突然想起，自己曾经改过hosts文件。打开/etc/hosts，添加：
127.0.0.1 localhost