我经常在Mac的本地环境中运行Rails > Postgresql，有时会遇到以下类似的错误困扰。

#<PG::ConnectionBad: could not connect to server: Connection refused
    Is the server running on host "localhost" (::1) and accepting
    TCP/IP connections on port 5432?
could not connect to server: Connection refused
    Is the server running on host "localhost" (fe80::1) and accepting
    TCP/IP connections on port 5432?
could not connect to server: Connection refused
    Is the server running on host "localhost" (127.0.0.1) and accepting
    TCP/IP connections on port 5432?

重启也没用。

$ brew services restart postgresql
$ ps aux | grep postgresql
soeda            13514   0.0  0.0  2443044    808 s001  S+    3:04PM   0:00.00 grep postgresql

没有进程

最终，卸载了postgresql并重新安装。

$ brew uninstall postgresql
$ rm -rf /usr/local/var/postgres
$ brew install postgresql

这样就修好了，但是重新建立数据库之类的工作很辛苦。

PID文件的样子

$ brew services start postgresql
$ ps aux | grep postgresql
soeda            13514   0.0  0.0  2443044    808 s001  S+    3:04PM   0:00.00 grep postgresql

实际上，即使尝试确认过程，起动也根本无法进行。

$ cat /usr/local/var/postgres/postmaster.pid 
13457
/usr/local/var/postgres
1510293800
5432
/tmp
localhost
  5432001     65536

PID文件还在…
（停止时通常会删除PID文件，但是PID文件似乎仍然存在）

$ brew services stop postgresql
$ rm /usr/local/var/postgres/postmaster.pid

把PID关掉试试看

$ brew services start postgresql
$ ps aux | grep postgresql
soeda            13514   0.0  0.0  2443044    808 s001  S+    3:04PM   0:00.00 grep postgresql
soeda            13457   0.0  0.1  2605700  13796   ??  S     3:03PM   0:00.03 /usr/local/opt/postgresql/bin/postgres -D /usr/local/var/postgres

动了！

考察 chá)

在brew无法管理的地方，postgresql进程崩溃了，导致使用PID文件进行的进程管理出现故障，所以无法启动？