My server is constantly showing 400-500% cpu usage

the culprit seems to be mysqld, which is runnign at 400%.
if i restart it, it jumps straight back upto 400%.

the site is not getting a lot of traffic at all.

any help is appreciated

What OS distro are you running? What version of MySQL? What type of site?

Giving us some good information about what you're doing will help us help you.

what does "show processlist" say on a mysql prompt?

Have you enabled the slow query log? If so what does it contain?

Ubuntu 13.04
its a Linode 8192

Its a site running Magento

mysql> SHOW VARIABLES LIKE "%version%";
+-------------------------+-----------------------------+
| Variable_name | Value |
+-------------------------+-----------------------------+
| innodb_version | 5.5.34 |
| protocol_version | 10 |
| slave_type_conversions | |
| version | 5.5.34-0ubuntu0.13.04.1-log |
| version_comment | (Ubuntu) |
| version_compile_machine | x86_64 |
| version_compile_os | debian-linux-gnu |
+-------------------------+-----------------------------+


mysql> show processlist;
+----+------------------+-----------+------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
| Id | User | Host | db | Command | Time | State | Info |
+----+------------------+-----------+------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
| 69 | root | localhost | NULL | Query | 0 | NULL | show processlist |
| 80 | expertelectrical | localhost | expertelectrical | Query | 0 | Sending data | SELECT `seonavigation`.* FROM `seonavigation` WHERE (`seonavigation`.`query_params`='a:5:{s:12:\"pro |
| 81 | expertelectrical | localhost | expertelectrical | Query | 0 | Sending data | SELECT `seonavigation`.* FROM `seonavigation` WHERE (`seonavigation`.`request_path`='power-supplies- |
+----+------------------+-----------+------------------+---------+------+--------------+------------------------------------------------------------------------------------------------------+
3 rows in set (0.00 sec)

slow query log simply show:

/usr/sbin/mysqld, Version: 5.5.34-0ubuntu0.13.04.1-log ((Ubuntu)). started with:
Tcp port: 3306 Unix socket: /var/run/mysqld/mysqld.sock
Time Id Command Argument

My guess is you are getting traffic from *somewhere*.

Check your Apache logs, see who is visiting what.