Repairing the MySQL WordPress Database

You can recover a running MySQL database with the mysqlcheck command.

After a power cut, I found these errors in /var/log/daemon.log. This was on Debian Squeeze running WordPress 3.3.1 and MySQL 5.1.61.

Mar 22 11:22:16 debian /etc/mysql/debian-start[2153]: Triggering myisam-recover for all MyISAM tables
Mar 22 11:22:17 debian mysqld: 120322 11:22:17 [ERROR] /usr/sbin/mysqld: Table './wordpress/wp_commentmeta' is marked as crashed and should be repaired
Continue reading

Process Substitution and Pipes

Command substitution is a widely used feature of the Bash and Korn shells, allowing the output of one command to be captured and used in another. Like this:

bash-4.2$ echo “Backup started at $(date)”
Backup started at Fri Mar 16 15:35:14 GMT 2012

Command substitution is not to be confused with that less well known (and, if we’re honest, less useful) shell feature, process substitution. Despite being rarely used, process substitution is worth knowing about, if only because it illuminates other fundamental unix features – the shell, sub processes, named and unnamed pipes.

This post discusses process substitution, command substitution and the vertical bar (|). Three very different shell features, but all making use of unnamed pipes, and so not as different as they first appear. The examples are from Linux but also work on Solaris 10 and, due to the ubiquity of pipes, are likely to work on other unixes too. Continue reading