完全备份具体步骤，只需要一行操作：

    步骤：
    保证mysql服务是正常的，然后执行下面的备份命令
    # innobackupex --user root --password 123456789 /allsql

完全恢复具体步骤：

    步骤一：
    # systemctl stop mysqld
    步骤二：
    # cd /allsql/
    # ls
    2021-12-27_22-22-40
    
    # innobackupex --apply-log /allsql/2021-12-27_22-22-40
    # rm -rf /var/lib/myslq/*
    # 步骤三：
    innobackupex --copy-back /allsql/2021-12-27_22-22-40
    步骤四：
    查看mysql配置文件"/etc/my.cnf"中含有"/var/lib/mysql/"的子目录是否存在，
    不存在则创建，因为前期删除了"/var/lib/mysql/"所有文件，避免配置文件中
    有些目录"innobackupex"没有备份，无法重启mysqld服务；
    # cat /etc/my.cnf | grep "/var/lib/mysql/"
    socket=/var/lib/mysql/mysql.sock
    log-bin=/var/lib/mysql/binlog/bin_log_sql
    我需要创建目录：
    mkdir /var/lib/mysql/binlog/
    步骤五：
    修改mysql目录文件的属主和属组
    # chown -R mysql:mysql /var/lib/mysql
    步骤六：
    重启服务：
    systemctl start mysqld

排查思路：
(1)
重启服务失败排查思路：查看"/etc/my.cnf"中的各种文件和目录是否存在，
如果不存在，需要创建，同时修改文件的属主和属组为"mysql:mysql"；
(2)
递归修改"/var/lib/mysql"权限
chown -R mysql:mysql /var/lib/mysql。

我的错误是mysql配置文件中"log-bin=/var/lib/mysql/binlog/bin_log_sql"文件在首次全量备份后不存在。 需要创建"/var/lib/mysql/binlog/"目录，同时将权限修改为"mysql:mysql"

我遇到的错误信息如下：

[root@W103 ~]# systemctl start mysqld
Job for mysqld.service failed because the control process exited with error code. See "systemctl status mysqld.service" and "journalctl -xe" for details.
[root@W103 ~]# 
[root@W103 ~]# journalctl -xe
-- 
-- Unit mysqld.service has failed.
-- 
-- The result is failed.
Dec 27 22:53:31 W103 systemd[1]: Unit mysqld.service entered failed state.
Dec 27 22:53:31 W103 systemd[1]: mysqld.service failed.
Dec 27 22:53:31 W103 systemd[1]: mysqld.service holdoff time over, scheduling restart.
Dec 27 22:53:31 W103 systemd[1]: Stopped MySQL Server.
-- Subject: Unit mysqld.service has finished shutting down
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysqld.service has finished shutting down.
Dec 27 22:53:31 W103 systemd[1]: start request repeated too quickly for mysqld.service
Dec 27 22:53:31 W103 systemd[1]: Failed to start MySQL Server.
-- Subject: Unit mysqld.service has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit mysqld.service has failed.
-- 
-- The result is failed.
Dec 27 22:53:31 W103 systemd[1]: Unit mysqld.service entered failed state.
Dec 27 22:53:31 W103 systemd[1]: mysqld.service failed.