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* MYSQL WON'T START OR STOP?:
=============================
You may never ever delete the special mysql user "debian-sys-maint". This
user together with the credentials in /etc/mysql/debian.cnf are used by the
init scripts to stop the server as they would require knowledge of the mysql
root users password else.
So in most of the times you can fix the situation by making sure that the
debian.cnf file contains the right password, e.g. by setting a new one
(remember to do a "flush privileges" then).
* WHAT TO DO AFTER UPGRADES:
============================
The privilege tables are automatically updated so all there is left is read
the changelogs on dev.mysql.com to see if any changes affect custom apps.
* WHAT TO DO AFTER INSTALLATION:
================================
The MySQL manual describes certain steps to do at this stage in a separate
chapter. They are not necessary as the Debian packages does them
automatically.
The only thing that is left over for the admin is
- setting the passwords
- creating new users and databases
- read the rest of this text
* DOWNGRADING TO 4.0 or 4.1:
============================
Unsupported. Period.
But if you do and get problems or make interesting experiences, mail me, it
might help others.
Ok, if you really want, I would recommend to "mysqldump --opt" all tables,
then purge 4.1, delete /var/lib/mysql, install 4.0 and insert the dumps. Be
carefully, though, with the "mysql" table, you might not simply overwrite that
one as the password for the mysql "debian-sys-maint" user is stored in
/etc/mysql/debian.cnf and needed by /etc/init.d/ to start mysql and check if
it's alive.
* SOME APPLICATION CAN NO LONGER CONNECT:
=========================================
This application is probably linked against libmysqlclient12 or below and
somebody has created a mysql user with new-style passwords.
The old_passwords=1 option in /etc/mysql/my.cnf might help. If not the
application that inserted the user has to be changed or the application that
tries to connect updated to libmysqlclient14 or -15.
* NETWORKING:
=============
For security reasons, the Debian package has enabled networking only on the
loop-back device using "bind-address" in /etc/mysql/my.cnf. Check with
"netstat -tlnp" where it is listening. If your connection is aborted
immediately see if "mysqld: all" or similar is in /etc/hosts.allow and read
hosts_access(5).
* WHERE IS THE DOCUMENTATION?:
==============================
Unfortunately due to licensing restrictions, debian currently not able
to provide the mysql-doc package in any format. For the most up to date
documentation, please go to http://dev.mysql.com/doc.
* PASSWORDS:
============
It is strongly recommended to set a password for the mysql root user (which
/usr/bin/mysql -u root -D mysql -e "update user set password=password('new-password') where user='root'"
/usr/bin/mysql -u root -e "flush privileges"
If you already had a password set add "-p" before "-u" to the lines above.
If you are tired to type the password in every time or want to automate your
scripts you can store it in the file $HOME/.my.cnf. It should be chmod 0600
(-rw------- username username .my.cnf) to ensure that nobody else can read
it. Every other configuration parameter can be stored there, too. You will
find an example below and more information in the MySQL manual in
/usr/share/doc/mysql-doc or www.mysql.com.
ATTENTION: It is necessary, that a .my.cnf from root always contains a "user"
line wherever there is a "password" line, else, the Debian maintenance
scripts, that use /etc/mysql/debian.cnf, will use the username
"debian-sys-maint" but the password that is in root's .my.cnf. Also note,
that every change you make in the /root/.my.cnf will affect the mysql cron
script, too.
# an example of $HOME/.my.cnf
[client]
user = your-mysql-username
password = enter-your-good-new-password-here
* BIG_ROWS FOR EVEN MORE ROWS IN A TABLE:
=========================================
If you ever run out of rows in a table there is the possibility of building
the package with "-DBIG_ROWS" which, according to a MySQL employee on
packagers@lists.mysql.com should lead to a 64bit row index (I guess > 2^32
rows) but also to an approx. 5% performance loss.
* BerkeleyDB Storage Engine
===========================
Support for BerkeleyDB has been removed in 5.1, and consequently both the
have-bdb and skip-bdb configuration options will cause the server to fail.
Removing the options from /etc/mysql/my.cnf will fix this problem.
* FURTHER NOTES ON REPLICATION
===============================
If the MySQL server is acting as a replication slave, you should not
set --tmpdir to point to a directory on a memory-based filesystem or to
a directory that is cleared when the server host restarts. A replication
slave needs some of its temporary files to survive a machine restart so
that it can replicate temporary tables or LOAD DATA INFILE operations. If
files in the temporary file directory are lost when the server restarts,
replication fails.
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