ubuntu下mysql无法启动&syslog报“multipath add missing path”怎么回事

由于给ubuntu虚拟机设置了快照，导致磁盘空间不足，进而导致ubuntu直接被挂起死机，删除快照并重启ubuntu后，则发现mysql无法启动。

使用sudo service mysql status命令后，报错是这样的：

× mysqld.service - MySQL Server
 Loaded: loaded (/usr/lib/systemd/system/mysqld.service; enabled; vendor preset: disabled)
 Active: failed (Result: exit-code) since Mon 2021-04-19 00:01:33 CST; 533ms ago
 Docs: man:mysqld(8)
 http://dev.mysql.com/doc/refman/en/using-systemd.html
Process: 14629 ExecStartPre=/usr/bin/mysqld_pre_systemd (code=exited, status=0/SUCCESS)
Process: 14650 ExecStart=/usr/bin/mysqld $MYSQLD_OPTS (code=exited, status=127)
 Main PID: 14650 (code=exited, status=127)
CPU: 112ms

4月 19 00:01:33 RISE systemd[1]: mysqld.service: Scheduled restart job, restart counter is at 5.
4月 19 00:01:33 RISE systemd[1]: Stopped MySQL Server.
4月 19 00:01:33 RISE systemd[1]: mysqld.service: Start request repeated too quickly.
4月 19 00:01:33 RISE systemd[1]: mysqld.service: Failed with result 'exit-code'.
4月 19 00:01:33 RISE systemd[1]: Failed to start MySQL Server. 

排查/var/log/syslog日志文件，发现大量如下报错：

Jun 11 12:27:28 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:28 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:28 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:28 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory
Jun 11 12:27:33 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:33 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:33 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:33 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory
Jun 11 12:27:38 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:38 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:38 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:38 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory
Jun 11 12:27:43 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:43 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:43 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:43 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory
Jun 11 12:27:48 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:48 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:48 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:48 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory
Jun 11 12:27:53 ubuntu multipathd[681]: sda: add missing path
Jun 11 12:27:53 ubuntu multipathd[681]: sda: failed to get udev uid: Invalid argument
Jun 11 12:27:53 ubuntu multipathd[681]: sda: failed to get sysfs uid: Invalid argument
Jun 11 12:27:53 ubuntu multipathd[681]: sda: failed to get sgio uid: No such file or directory 

经过百度搜索得知，是multipath 的配置问题，需要排除本地的sda磁盘（此问题有可能是ubuntu是虚拟机导致的，直接在物理机上部署ubuntu从来没遇到过）。

解决multipath多路径配置问题

1.修改/etc/multipath.conf文件

sudo vi /etc/multipath.conf 

2.添加以下内容，sda视本地环境做调整

blacklist {
devnode "sda"
} 

3.重启multipath-tools服务

sudo service multipath-tools restart 

再次查看/var/log/syslog日志，发现没有报错了，但尝试重启mysql仍然无法启动，排查发现/var/log/syslog提示没有/etc/mysql/my.cnf这个文件，日志截图如下：

Jun 11 12:36:12 ubuntu multipathd[681]: --------shut down-------
Jun 11 12:36:12 ubuntu systemd[1]: Stopping Device-Mapper Multipath Device Controller...
Jun 11 12:36:12 ubuntu systemd[1]: multipathd.service: Succeeded.
Jun 11 12:36:12 ubuntu systemd[1]: Stopped Device-Mapper Multipath Device Controller.
Jun 11 12:36:12 ubuntu systemd[1]: Starting Device-Mapper Multipath Device Controller...
Jun 11 12:36:12 ubuntu multipathd[2463]: --------start up--------
Jun 11 12:36:12 ubuntu multipathd[2463]: read /etc/multipath.conf
Jun 11 12:36:12 ubuntu multipathd[2463]: path checkers start up
Jun 11 12:36:12 ubuntu systemd[1]: Started Device-Mapper Multipath Device Controller.
Jun 11 12:36:38 ubuntu systemd[1]: Starting MySQL Community Server...
Jun 11 12:36:38 ubuntu mysql-systemd-start[2498]: MySQL configuration not found at /etc/mysql/my.cnf. Please create one.
Jun 11 12:36:38 ubuntu systemd[1]: mysql.service: Control process exited, code=exited, status=1/FAILURE
Jun 11 12:36:38 ubuntu systemd[1]: mysql.service: Failed with result 'exit-code'.
Jun 11 12:36:38 ubuntu systemd[1]: Failed to start MySQL Community Server.
Jun 11 12:36:38 ubuntu systemd[1]: mysql.service: Scheduled restart job, restart counter is at 1.
Jun 11 12:36:38 ubuntu systemd[1]: Stopped MySQL Community Server.
Jun 11 12:36:38 ubuntu systemd[1]: Starting MySQL Community Server... 

手动创建配置文件

cd /etc
sudo mkdir mysql
cd mysql
sudo touch my.cnf 

使用sudo service mysql start 命令重启mysql，发现已经可以正常启动了。

lanyirenjg@ubuntu:/etc/mysql$ sudo service mysql start
lanyirenjg@ubuntu:/etc/mysql$ sudo service mysql status
● mysql.service - MySQL Community Server
 Loaded: loaded (/lib/systemd/system/mysql.service; enabled; vendor preset: enabled)
 Active: active (running) since Sat 2022-06-11 12:43:20 UTC; 6s ago
Process: 2875 ExecStartPre=/usr/share/mysql/mysql-systemd-start pre (code=exited, status=0/SUCCESS)
Process: 2897 ExecStart=/usr/sbin/mysqld --daemonize --pid-file=/run/mysqld/mysqld.pid (code=exited, status=0/SUCCESS)
 Main PID: 2899 (mysqld)
Tasks: 27 (limit: 4612)
 Memory: 198.0M
 CGroup: /system.slice/mysql.service
 └─2899 /usr/sbin/mysqld --daemonize --pid-file=/run/mysqld/mysqld.pid

Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.634817Z 0 [Warning] CA certificate ca.pem is self signed.
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.634934Z 0 [Note] Skipping generation of RSA key pair as key files are present in data directory.
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.636509Z 0 [Note] Server hostname (bind-address): '*'; port: 3306
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.636673Z 0 [Note] IPv6 is available.
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.636738Z 0 [Note] - '::' resolves to '::';
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.636779Z 0 [Note] Server socket created on IP: '::'.
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.669118Z 0 [Note] Event Scheduler: Loaded 0 events
Jun 11 12:43:20 ubuntu mysqld[2899]: 2022-06-11T12:43:20.669508Z 0 [Note] /usr/sbin/mysqld: ready for connections.
Jun 11 12:43:20 ubuntu mysqld[2899]: Version: '5.7.38-0ubuntu0.18.04.1'socket: '/var/run/mysqld/mysqld.sock'port: 3306(Ubuntu)
Jun 11 12:43:20 ubuntu systemd[1]: Started MySQL Community Server.