MySQL startup prompt: mysql. host does not exist. startup failed [problem solved]

After I delete the S9 public mysql4.0, I re-installed a new mysql5.0. During the startup process, an error is reported, indicating that the startup failed, I checked the old posts in the group and did not provide a specific explanation. I also asked the expert to explain how to solve the problem. Thank you.
Records in the error log:

[Error] fatal error: Can't open and lock privilege tables: Table 'mysql. host' doesn' t exist

I posted a post. I only saw it, but no one replied. I can only solve the problem by myself. Can I help myself... You don't have to mention it. It actually solved the problem. People are all forced out ,.... there is no way. This problem may be a very simple problem for the experts, but for the first time I touched MySQL, I did not understand it.
Now, let's talk about the process of solving the problem:

Follow the MySQL installation steps:
Shell> groupadd MySQL
Shell> useradd-G MySQL
Shell> gunzip | mysql-VERSION.tar.gz | tar-xvf-
Shell> Cd mysql-version
Shell>./configure -- prefix =/usr/local/MySQL
Shell> make
Shell> make install
Shell> scripts/mysql_install_db -- user = MySQL
Shell> chown-r root/usr/local/MySQL
Shell> chown-r MySQL/usr/local/MySQL/var
Shell> chgrp-r MySQL/usr/local/MySQL
Shells> CP support-files/my-medium.cnf/etc/My. CNF
Shell>/usr/local/MySQL/bin/mysqld_safe -- user = MySQL &

There is no problem with this standard, but when I start MySql in the last step, I want to put the database data file under another directory and change the startup command:
Shell>/usr/local/MySQL/bin/mysqld_safe -- user = MySQL -- log-error =/u01/MySQL/mysql_error/error -- datadir =/u01/MySQL/Data

This problem occurs because the permission table created by default is under the default directory/usr/local/MySQL/var when initializing the database permission table, this leads to the failure to find the permission table: Can't open and lock privilege tables: Table 'mysql. host 'doesn' t exist

solution: When you run the initialization permission table, use the added parameter datadir. The command format is:
shell> scripts/mysql_install_db -- user = MySQL -- datadir =/u01/MySQL/Data
the problem is solved.
this problem also occurs when you change the data file of your database to another directory, because you have not created a database permission table in the corresponding directory, the solution is to re-run the mysql_install_db file to regenerate the database permission table, but you also need to re-create the user and Set permissions; the second method should be to copy the files in the old permission table to the corresponding database table directory first, but the second method I did not use is just based on my own imagination. If you have a master, check whether the master is correct.