Cannot get a TCPdump from MySQL

Question

I am having quite a few problems on a tricky server.

One of my main problems at the moment is that tcpdump cannot seem to get the packets sent to mysql, unless I tinker with MySQL a bit.

This is what I run:

tcpdump -s 65535 -x -nn -q -tttt -i any -c 99999 port 3306

When I run this, no output is shown.

If however, I log into mysql using

mysql -h 127.0.0.1

..then tcpdump does show some output.

My problem is that the current traffic coming from apache does not show up using tcpdump and I do not know if I need to change a parameter in tcpdump, MySQL or apache.

Some more info:

netstat -tap | grep mysql

tcp 0 0 *:mysql *:* LISTEN 2238/mysqld 

cat /etc/hosts

127.0.0.1 localhost localhost.localdomain 

Can anyone please help?

Answer 1

You're not seeing the traffic using tcpdump because MySQL isn't using TCP, it's using a Unix socket. You need to configure the database client (presumably a PHP application, although I guess in theory you could be using Apache itself to talk to MySQL) to connect to 127.0.0.1, because localhost (typically the default) is a special value that means "use a Unix socket" to the MySQL client library.