錯誤一：正常步驟安裝完mysql，發現啓動mysql服務時出現以下情況：
遇到這樣的錯誤，是由於 /etc/init.d/ 不存在 mysqld 這個命令（有的人安裝完環境後存在，是因爲你的安裝包中有這樣的命令將 mysql.server 文件 copy 到 /etc/init.d/ 下面了）
[root@hadoop102 mysql]# find / -name mysql.server
/usr/local/mysql/support-files/mysql.server
然後複製剛纔找到的文件到/etc/init.d/ 目錄下，替換掉mysqld文件即可。
[root@hadoop102 mysql]# cp /usr/local/mysql/support-files/mysql.server /etc/init.d/mysqld
cp：是否覆蓋"/etc/init.d/mysqld"？ yes
重新啓動服務即可。
第二個問題：
導致這個問題得原因有很多，在這裏我查看了mysql的日誌文件，顯示出我的錯誤信息：
cd /var/log/
[root@hadoop102 log]# cat mysqld.log
2020-03-29T05:17:08.611117Z 0 [Note] InnoDB: Completed initialization of buffer pool
2020-03-29T05:17:08.624600Z 0 [Note] InnoDB: If the mysqld execution user is authorized, page cleaner thread priority can be changed. See the man page of setpriority().
2020-03-29T05:17:08.643898Z 0 [Note] InnoDB: Highest supported file format is Barracuda.
2020-03-29T05:17:08.670178Z 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2020-03-29T05:17:08.670335Z 0 [Note] InnoDB: Setting file './ibtmp1' size to 12 MB. Physically writing the file full; Please wait ...
2020-03-29T05:17:08.747618Z 0 [Note] InnoDB: File './ibtmp1' size is now 12 MB.
2020-03-29T05:17:08.754325Z 0 [Note] InnoDB: 96 redo rollback segment(s) found. 96 redo rollback segment(s) are active.
2020-03-29T05:17:08.754355Z 0 [Note] InnoDB: 32 non-redo rollback segment(s) are active.
2020-03-29T05:17:08.760900Z 0 [Note] InnoDB: Waiting for purge to start
2020-03-29T05:17:08.811363Z 0 [Note] InnoDB: 5.7.20 started; log sequence number 2565377
2020-03-29T05:17:08.818253Z 0 [Note] InnoDB: Loading buffer pool(s) from /usr/local/mysql/data/ib_buffer_pool
2020-03-29T05:17:08.818700Z 0 [Note] Plugin 'FEDERATED' is disabled.
2020-03-29T05:17:08.819204Z 0 [Note] InnoDB: Buffer pool(s) load completed at 200329 13:17:08
2020-03-29T05:17:08.844001Z 0 [Warning] Failed to set up SSL because of the following SSL library error: SSL context is not usable without certificate and private key
2020-03-29T05:17:08.844166Z 0 [Note] Server hostname (bind-address): '*'; port: 3306
2020-03-29T05:17:08.849886Z 0 [Note] IPv6 is available.
2020-03-29T05:17:08.849923Z 0 [Note] - '::' resolves to '::';
2020-03-29T05:17:08.849940Z 0 [Note] Server socket created on IP: '::'.
2020-03-29T05:17:08.857458Z 0 [ERROR] /usr/local/mysql/bin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 2 - No such file or directory)
2020-03-29T05:17:08.857478Z 0 [ERROR] Can't start server: can't create PID file: No such file or directory
很明顯，錯誤發生在最後兩行，/usr/local/mysql/bin/mysqld: Can't create/write to file '/var/run/mysqld/mysqld.pid' (Errcode: 2 - No such file or directory)，可能是我的這個目錄下面根本沒有mysqld這個文件，於是追根問底來到了/var/run文件夾下，正如預料，沒有mysqld文件夾，所以創建文件夾，並且賦予權限，到此解決問題，正常啓動，
[root@hadoop102 run]# ls -l mysqld*
ls: 無法訪問mysqld*: 沒有那個文件或目錄
[root@hadoop102 run]# mkdir mysqld
[root@hadoop102 run]# chown -R mysql:mysql /var/run/mysqld
[root@hadoop102 run]# ll
錯誤三：
mysql服務已經正常安裝，爲何報出此錯誤？谷歌到以下兩種解決辦法：
第一種方式
以完整路徑的方式運行命令，比如我的路徑，/usr/local/mysql/bin/mysql
第二種方式用ln
ln -s /usr/local/mysql/bin/mysql /usr/bin
相當於建立一個鏈接文件。-s進行軟鏈結
錯誤四：
這種提示通常是沒有 輸入密碼導致的。
這個提示通常是由於輸入錯誤密碼導致的。所以下面進行修改密碼：
//在配置文件中輸入以下跳過身份驗證，然後關閉mysql服務後再次重新啓動服務。
skip-grant-tables
進入mysql修改密碼
//進入mysql
mysql
//修改密碼
mysql> use mysql;
set password for ‘root’@‘localhost’=password(‘root’);
如果出現以下錯誤信息：輸入：flush privileges;
最後修改成功後別忘記進入配置文件註釋掉剛纔添加的內容，最後成功登陸：
目前遇到這兩個問題，以後遇到問題在更新........