ERROR 1698 (28000): Access denied for user ‘root‘@‘localhost‘ ，Ubuntu20.04中MySQL8.0报错解决。

service mysql restart重启命令

sudo vim /etc/mysql/mysql.conf.d/mysqld.cnf

在 [mysqld] 最后面加入skip-grant-tables.

[mysqld]
#
# * Basic Settings
#
user            = mysql
# pid-file      = /var/run/mysqld/mysqld.pid
# socket        = /var/run/mysqld/mysqld.sock
# port          = 3306
# datadir       = /var/lib/mysql


# If MySQL is running as a replication slave, this should be
# changed. Ref https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_tmpdir
# tmpdir                = /tmp

#
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address            = 127.0.0.1
mysqlx-bind-address     = 127.0.0.1
#
# * Fine Tuning
#
key_buffer_size         = 16M
# max_allowed_packet    = 64M
# thread_stack          = 256K

# thread_cache_size       = -1

# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched
myisam-recover-options  = BACKUP

# max_connections        = 151

# table_open_cache       = 4000

#
# * Logging and Replication
#
# Both location gets rotated by the cronjob.

#
# Log all queries
# Be aware that this log type is a performance killer.
# general_log_file        = /var/log/mysql/query.log
# general_log             = 1
#
# Error log - should be very few entries.
#
log_error = /var/log/mysql/error.log
#
# Here you can see queries with especially long duration
# slow_query_log                = 1
# slow_query_log_file   = /var/log/mysql/mysql-slow.log
# long_query_time = 2
# log-queries-not-using-indexes
#
# The following can be used as easy to replay backup logs or for replication.
# note: if you are setting up a replication slave, see README.Debian about
#       other settings you may need to change.
# server-id             = 1
# log_bin                       = /var/log/mysql/mysql-bin.log
# binlog_expire_logs_seconds    = 2592000
max_binlog_size   = 100M
# binlog_do_db          = include_database_name
# binlog_ignore_db      = include_database_name
skip-grant-tables

然后  mysql -u root -p  回车进入
flush privileges;
ALTER USER 'root'@'localhost' IDENTIFIED WITH mysql_native_password BY '123456';

之后quit退出，删除skip-grant-tables，用新密码登录。

另一个错误：ERROR 1449 (HY000): The user specified as a definer (‘mysql.infoschema’@‘localhost’) does not exist

在执行show databases;时会报这个错。
解决办法：

create user 'mysql.infoschema'@'%' identified by '密码';

grant all privileges on *.* to 'mysql.infoschema'@'%';

flush privileges;

再次执行即可。