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What are the reasons for the failure of MySQL startup, many novices are not very clear about this, in order to help you solve this problem, the following editor will explain for you in detail, people with this need can come to learn, I hope you can gain something.

Unable to access system resources

The failure of MySQL to access the resources needed for startup is a common reason why MySQL cannot be started, such as files, ports, etc. Since the mysql user used to start the mysqld process in linux is usually not logged in, you can use a command similar to the following to check file access.

Sudo-u mysql touch / var/lib/mysql/b

After the problem has been identified, changing the permissions or ownership of the corresponding file or directory can usually solve the problem. However, sometimes mysql users have access to files and directories, but they are still denied access, such as the following example:

Mysql > system sudo-u mysql touch / home/mysql/data/a mysql > create table T1 (id int primary key,n varchar (10) data directory ERROR 1030 (HY000): Got error 168from storage engine

The test shows that the mysql user has access to this directory, but the creation of the file still fails. This situation puzzles many people. At this time, the access of the mysqld process is usually blocked by the selinux or apparmor of linux. You can see that the created table is not under the default directory of mysql, so the policy of selinux or apparmor does not contain the access permission for this directory. Just modify the policy at this time. Of course, you can stop selinux or apparmor.

Sometimes, although you have access to system resources, system resources are already occupied:

Mysqld-no-defaults-console-user mysql 2020-11-03T03:36:07.519419Z 0 [System] [MY-010116] [Server] / usr/sbin/mysqld (mysqld 8.0.19) starting as process 21171 2020-11-03T03:36:07.740347Z 1 [ERROR] [MY-012574] [InnoDB] Unable to lock. / ibdata1 error: 11

The cause of this failure is that another mysqld process has already started and occupied the corresponding file.

Second, parameter setting error

It is also very common that MySQL cannot be started due to incorrect parameter settings. First, check the parameters that will be called when MySQL starts. The following command can query the order in which parameter files are called when MySQL starts:

$mysqld-- verbose-- help | grep "Default options"-A1 Default options are read from the following files in the given order: / etc/my.cnf / etc/mysql/my.cnf ~ / .my.cnf

Knowing the order in which the MySQL parameter file is called, we can check the corresponding parameter file and find out the errors. If we feel that the parameter file is not readable, we can use the following command to display the parameters that the mysqld program will call:

$mysqld-print-defaults / usr/sbin/mysqld would have been started with the following arguments:.

Note that this command exits after displaying the parameters and will not actually run mysqld. This command is completely equivalent to my_print_defaults mysqld, except that the latter is displayed as one parameter per line.

Then start debugging the suspicious parameters. I personally like to add the parameters and order as follows:

1. Add the first parameter-no-defaults after mysqld. The function of this parameter is to tell mysqld not to read any parameter files when starting.

two。 The second parameter is-- console, which outputs the error message to the screen. One drawback of this parameter is that all the information is output to the screen, which makes the screen look messy, but it is very convenient for us to debug.

3. The third parameter is-- log-error-verbosity=3, which displays the detailed log

4. Then add certain parameters later, you can add only one parameter at a time, and then start mysqld, using the elimination method to find out the wrong parameters step by step.

Look at this example:

Mysqld-- no-defaults-- console-- log-error-verbosity=3-- user mysql-- gtid_mode=on 2020-11-03T07:14:20.384223Z 0 [Note] [MY-010949] [Server] Basedir set to / usr/. 2020-11-03T07:14:20.384254Z 0 [System] [MY-010116] [Server] / usr/sbin/mysqld (mysqld 8.0.19) starting as process 22617 2020-11-03T07:14:20.400221Z 0 [Note] [InnoDB] Using Linux native AIO. 2020-11-03T07:14:21.632851Z 0 [ERROR] [MY-010912] [Server] GTID_MODE = ON requires ENFORCE_GTID_CONSISTENCY = ON. 2020-11-03T07:14:21.634183Z 0 [ERROR] [MY-010119] [Server] Aborting. 2020-11-03T07:14:23.026551Z 0 [System] [MY-010910] [Server] / usr/sbin/mysqld: Shutdown complete (mysqld 8.0.19) MySQL Community Server-GPL. Root@scutech:~#

Looking at this example, we can easily see that we need to set the parameters GTID_MODE and ENFORCE_GTID_CONSISTENCY to on at the same time.

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