今天碰到一個問題，伺服器異常關閉，mysql無法啟動，檢視mysql 狀態service mysqld status都提示：MySQL is running but PID file could not be found。
解決方法：

1. 使用ps -elf |grep mysql 查詢mysql的程序，瞭解到pid檔案在 /usr/local/var 目錄下， 記一下，等會需要這個目錄
   

2. 打算先停掉服務，再重啟服務

   service mysqld stop

提示：MySQL manager or server PID file could not be found!
解決： 使用 ps -elf |grep mysql |grep -v grep

service  mysqld start

3. 然而還是不行，一直停留在
   
   檢視狀態
   
   於是去把lock 先刪掉

[[email protected] ~]# cd  /var/lock/subsys/
[[email protected] subsys]# ls
crond  local  mysql  network  nscd  ntpd  rsyslog  sshd
[[email protected] subsys]# mysql
ERROR 2002 (HY000): Can't connect to local MySQL server through socket '/tmp/mysql.sock' (2)
[
 
[email protected] subsys]# rm -rf ./mysql
[[email protected] subsys]# ls
crond  local  network  nscd  ntpd  rsyslog  sshd

檢視mysql 狀態service mysqld status都提示：MySQL is running but PID file could not be found
這個時候去把 mysql 中 data 目錄下的 mysql-bin.index 檔案找到，然後刪除

[[email protected] subsys]# find / -name mysql-bin.index
/usr/local/var/mysql-bin.index
[
 
[email protected] subsys]# rm -rf /usr/local/var/mysql-bin.index

然後找到 並 kill 所有關於 mysql 或者 mysqld 的程序

ps -aux | grep mysql

4. 到這一般來說基本可以了，但是啟動mysql服務時候還是出現MySQL is running but PID file could not be found
   這時候就要另闢蹊徑 了。
   剛第一步的時候說到，pid 檔案所在的目錄，開啟這個目錄，我們看到確實沒有找到 xxxxx.pid 檔案，但是有一個 xxxx.err檔案，於是開啟看一下，都有哪些執行錯誤記錄，然後找到了最關鍵的一條：

181121 10:48:28 [Warning] '--skip-locking' is deprecated and will be removed in a future release. Please use '--skip-external-locking' instead.
 /usr/local/libexec/mysqld: Disk is full writing './mysql-bin.~rec~' (Errcode: 28). Waiting for someone to free space... (Expect up to 60 secs delay for server to continue after freeing disk space)
 /usr/local/libexec/mysqld: Retry in 60 secs. Message reprinted in 600 secs
 /usr/local/libexec/mysqld: Retry in 60 secs. Message reprinted in 600 secs
 /usr/local/libexec/mysqld: Retry in 60 secs. Message reprinted in 600 secs
 /usr/local/libexec/mysqld: Retry in 60 secs. Message reprinted in 600 secs
181121 11:00:31 mysqld_safe mysqld from pid file /usr/local/var/iZ253su9kjuZ.pid ended

那就是 Disk is full writing './mysql-bin.~rec~' (Errcode: 28). Waiting for someone to free space...
我進mysql資料目錄檢視，發現有很多以前的二進位制日誌，所以打算清空2017年前所有的二進位制日誌。
解決辦法：
先rm刪除binlog日誌，再purge binary logs to '具體的binlog’刪除。
注意：purge binary logs to 'mysql-bin.00003’表示清理mysql-bin.00003之前的所有binlog，但不包括mysql-bin.00003本身。
注意：如果只rm，不purge，重啟mysql的話，會報錯的,mysql就起不來了。所以rm刪除後，需要及時執行purge命令。

[[email protected] var]# purge binary logs to 'mysql-bin.00034'

於是就OK了，mysql服務終於重新啟動了，資料也沒有丟失

[[email protected] var]# service mysqld status
MySQL is not running                                       [ʧ▒▒]
[[email protected] var]# service mysqld start
Starting MySQL.                                            [ȷ▒▒]
[[email protected] var]# mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 2
Server version: 5.1.51-log Source distribution

Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use mysql
Database changed

補充一個mysql修改使用者密碼的命令