How to set up a MySQL database server on Ubuntu for Drupal to WordPress migrations

Content Management System (CMS) migration projects involve moving data between databases with different schemas. Table names, field types and constraints often don’t match up, leading to a number of frustrating errors. This is especially the case with highly complex Drupal to WordPress migrations that use custom scripts to extract, transform and load the data. These projects can seem like you’re constantly hitting roadblocks throughout. I’ve found from experience that running the migration in an appropriate development environment can reduce a great deal of effort. In this guide, I will describe how to set up a MySQL database server on Ubuntu for Drupal to WordPress migrations.

Table of contents

Why MySQL and Ubuntu?

The first thing to address is why MySQL and Ubuntu? How about MariaDB? How about Arch Linux, Mac OS or Windows? Yes! Any platform that runs Drupal and WordPress will work for your migration environment so you can use whatever you prefer. Personally, I have a fondness for OpenBSD but it’s not a practical platform for a CMS migration. OpenBSD’s niche user-base means you’ll spend much longer installing necessary tools and troubleshooting errors.

There are all sorts of tutorials covering MySQL on Ubuntu. This means you’re more likely to quickly find a solution from a web search when you hit a problem. Furthermore, if you need a software utility or program to help you get the job done, it will probably be available through apt, dpkg, snap or tasksel. Use whatever you like but for now, MySQL on Ubuntu is my recommended platform for Drupal to WordPress migrations. I expect this will be the case for some time to come. These projects are complex and time-consuming enough without making the job more difficult.

Installing MySQL on Ubuntu for CMS migrations

There are many detailed tutorials for installing MySQL on Ubuntu. DigitalOcean’s How To Install MySQL on Ubuntu 20.04 is a good one and writing another won’t add much value. My guide will therefore only give a brief overview of the MySQL server installation steps. Instead, I will focus on the configuration areas specifically related avoiding problems on a CMS migration project.

You may wonder why the migration environment should be much different from a live server. Migration projects require you to do things that aren’t supported by the CMS platform. You’re therefore likely to encounter weird errors that aren’t normally found when running standard Drupal or WordPress.

Set up your Ubuntu LAMP migration platform

The main source of unusual errors is almost certainly because you’re migrating on a setup suited to a live website. Live server configurations are more restrictive than you need for a migration project. You can therefore save yourself a huge headache by rolling your own local migration environment. It might take a little longer to get started but you’ll save time by avoiding lots of unnecessary troubleshooting.

I must highlight that this will be a local migration environment and should not be accessible from the public internet. The normal security considerations with running a live content management system don’t apply when you’re working locally. By all means follow basic security measures mentioned the various tutorials for setting up Ubuntu and MySQL. Nevertheless, a highly secure setup is counterproductive for these projects and you can avoid trouble by being a little more permissive.

Go ahead and install Ubuntu Desktop. Since this will be a development environment, you’ll want the Desktop environment rather than the more lightweight server version. Of course, you’ll still need to install a web and database server. Follow these instructions for installing LAMP stack but skip the step of installing MariaDB. As mentioned above, we’ll be using MySQL.

WARNING: Installing MariaDB over MySQL or vice versa on Ubuntu 20.04 may lead to all sorts of problems starting up the database server with errors like the following:

Failed to start mysqld.service: Unit mysqld.service not found.

The last time I did this, none of solutions mentioned online for purging the installation worked. I spent most of a day trying to fix the problem. In the end, I realised it was quicker to start again and rebuild the machine from scratch. This is a big reason why I decided to stick with MySQL as standard for my projects.

Install MySQL

You can read a more detailed tutorial on installing MySQL on Ubuntu but here’s an overview.

  1. Update the package index on your server: sudo apt update
  2. Install MySQL server: sudo apt install mysql-server
  3. Secure MySQL: sudo /usr/bin/mysql_secure_installation

The mysql_secure_installation script doesn’t cause problems for migrations so it’s worth running.

Create an admin user:

CREATE USER 'user'@'localhost' IDENTIFIED BY 'userpassword';
GRANT ALL PRIVILEGES ON *.* to 'user'@'localhost' WITH GRANT OPTION;
FLUSH PRIVILEGES;
quit;

Now create a user and database for your migration project:

CREATE USER 'projectuser'@'localhost' IDENTIFIED BY 'password';

CREATE DATABASE project_db CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_520_ci;
GRANT ALL ON project_db.* TO 'projectuser'@'localhost';

You can give this user more restrictive permissions but GRANT ALL avoids errors when running scripts and SQL queries on the database. Only the migration team should have access and you won’t need it after the migration so why not make your life easier?

Setting the MySQL server SQL mode

It’s possible that you won’t be familiar with SQL modes unless you’ve done some database administration work. For our purposes, SQL modes do two things:

  • change the types of queries you can run on your MySQL server;
  • change the validation checks when altering the data.

I’ve found that specific SQL modes need to be set for Drupal to WordPress projects. You may find that all sorts of strange errors appear if the correct modes aren’t set. The following sections show you two ways to set your MySQL server’s SQL mode.

Option 1: Setting the global sql_mode in the database

  1. Login in to database as an admin user.
  2. View the current sql-modes using SELECT @@GLOBAL.sql_mode; and make a copy if necessary.
  3. Copy the current modes (add or delete modes as needed) and paste in next step.
  4. Add ALLOW_INVALID_DATES and removes both NO_ZERO_DATE, NO_ZERO_IN_DATE by setting the sql-modes with
    SET GLOBAL sql_mode = 'STRICT_TRANS_TABLES,ALLOW_INVALID_DATES,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION'; (WARNING: check the modes correspond with your setup.)
  5. Restart server:
    sudo systemctl start mysql

Option 2: setting the sql_mode in the MySQL configuration file

Locating the MySQL configuration file

The my.cnf configuration file isn’t always found in the same place. It’s specific to the Linux distribution and server configuration but can normally found in one of the following locations:

/etc/my.cnf
/etc/mysql/my.cnf
echo/my.cnf
[datadir]/my.cnf
~/.my.cnf

If you can’t find your MySQL configuration file, you can try running locate my.cnf or mysqladmin --help. The latter will show something like the following in the output:

Default options are read from the following files in the given order:
/etc/my.cnf /etc/mysql/my.cnf ~/.my.cnf

Also keep in mind that it’s possible to use !include directives to include other option files and !includedir to search specific directories for option files. Under Ubuntu, there may be a file /etc/mysql/my.cnf with !includedir directives to search /etc/mysql/conf.d/ and /etc/mysql/mysql.conf.d/

Editing the MySQL configuration file

If the MySQL server finds more than one configuration file, it will load each one in turn. The values override each other and it can be difficult to know which takes priority. Furthermore, the –defaults-file parameter can also override all configurations. Keep things simple and have only one file and place it the directory that makes sense to you.

Before editing the my.cnf, first log in to MySQL with an administrator user and run the SELECT @@GLOBAL.sql_mode query to see the values used in your setup.

Setting the MySQL database server sql mode on Ubuntu for Drupal to WordPress migrations
Running the SELECT @@GLOBAL.sql_mode query on MySQL Workbench

Next, open the configuration file, look for the section [mysqld] and edit the line starting with:
sql_mode = ...

Add the line if it’s not there. Adjust the exact modes to match your project’s needs so take a look at the list of SQL modes to see which may apply. I’ve found the following works well:
sql_mode = "STRICT_TRANS_TABLES,ALLOW_INVALID_DATES,ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION"

Finally, restart the MySQL server. On Ubuntu this will probably be with

sudo systemctl start mysql

If you are logged in to the MySQL server, you may also need to disconnect your client and reconnect for the changes to take effect for your session.

Potential errors

Here are some potential errors that you may come across during a CMS migration project. I usually find them when running a Drupal to WordPress migration on a freshly built development environment.

mysqldump access denied when trying to dump tablespaces

Migrations involve dumping and importing databases and this process is straightforward on a mature development environment. However you may receive an ‘Access denied’ error out of the blue when dumping your MySQL database:

mysqldump: Error: 'Access denied; you need (at least one of) the PROCESS privilege(s) for this operation' when trying to dump tablespaces

If you see this, perhaps you were working on an environment that was a little too ‘mature’ (in other words, obsolete!) and you have recently upgraded your installation. The updates for MySQL 5.7.31 and MySQL 8.0.21 in July 2020 introduced an incompatible change that produces this error.

Read my separate article, How to fix the mysqldump access denied process privilege error, for more information and instructions on how you can try solving this.

ERROR 1067 (42000) Invalid default value

Drupal nodes store the date as a Unix timestamp in an int (e.g. 1623427200) field whereas WordPress stores dates as datetime (e.g. 2021-06-11 16:00:00). There may be a conversion error in your migration script or the source date could simply be zero for some reason. Normally your MySQL server mode will be set to NO_ZERO_DATE, NO_ZERO_IN_DATE so trying to insert a zero date will give you the error:

ERROR 1067 (42000) Invalid default value

You can fix this by replacing NO_ZERO_DATE, NO_ZERO_IN_DATE with set to ALLOW_INVALID_DATES in your global SQL mode.

Expression #1 of SELECT list is not in GROUP BY clause

You run an SQL query and get the rather cryptic error:

Expression #1 of SELECT list is not in GROUP BY clause and contains
nonaggregated column 'database.table.pid' which is not functionally dependent
on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

What’s wrong? MySQL has a only_full_group_by mode which, when enabled, strictly applies ANSI SQL rules when using GROUP BY. Fix this by reworking your script or removing the ONLY_FULL_GROUP_BY SQL mode.

Error Code: 2013. Lost connection to MySQL server

This often happens when it an SQL query takes too long to return data. The connection between your MySQL client and database server times out so the connection gets dropped. For ideas on how to try solving this, read my separate article, How to fix Error Code 2013 Lost connection to MySQL server.

Conclusion

Setting up a MySQL database server for Drupal or WordPress is a familiar task for web developers and site administrators. However, CMS migrations have quirks that can cause obscure and baffling errors. In this guide I’ve shown you some little tricks that may save time and annoyance. While there’s no way to provide an exhaustive list of solutions to all the MySQL problems you’ll encounter, I hope to have pointed you in the right direction.

If you have a site migration project and would like to hire me, please ask for a quote for my consulting service.

CMS migration consulting

All content · Custom content types · SEO · Plugins

Migrating content from a site and need a specialist? Please contact me for a quotation. Whether you’re a media agency who needs a database expert or a site owner looking for advice, I’ll save you time and ensure accurate content exports.

Get a quote

How to fix Error Code 2013 Lost connection to MySQL server

If you spend time running lots of MySQL queries, you might come across the Error Code: 2013. Lost connection to MySQL server during query. This article offers some suggestions on how to avoid or fix the problem.

Why this happens

This error appears when the connection between your MySQL client and database server times out. Essentially, it took too long for the query to return data so the connection gets dropped.

Most of my work involves content migrations. These projects usually involve running complex MySQL queries that take a long time to complete. I’ve found the WordPress wp_postmeta table especially troublesome because a site with tens of thousands of posts can easily have several hundred thousand postmeta entries. Joins of large datasets from these types of tables can be especially intensive.

Avoid the problem by refining your queries

In many cases, you can avoid the problem entirely by refining your SQL queries. For example, instead of joining all the contents of two very large tables, try filtering out the records you don’t need. Where possible, try reducing the number of joins in a single query. This should have the added benefit of making your query easier to read. For my purposes, I’ve found that denormalizing content into working tables can improve the read performance. This avoids time-outs.

Re-writing the queries isn’t always option so you can try the following server-side and client-side workarounds.

Server-side solution

If you’re an administrator for your MySQL server, try changing some values. The MySQL documentation suggests increasing the net_read_timeout or connect_timeout values on the server.

Client-side solution

You can increase your MySQL client’s timeout values if you don’t have administrator access to the MySQL server.

MySQL Workbench

You can edit the SQL Editor preferences in MySQL Workbench:

  1. In the application menu, select Edit > Preferences > SQL Editor.
  2. Look for the MySQL Session section and increase the DBMS connection read time out value.
  3. Save the settings, quite MySQL Workbench and reopen the connection.

Navicat

How to edit Navicat preferences:

  1. Control-click on a connection item and select Connection Properties > Edit Connection.
  2. Select the Advanced tab and increase the Socket Timeout value.

Command line

On the command line, use the connect_timeout variable.

Python script

If you’re running a query from a Python script, use the connection argument:
con.query('SET GLOBAL connect_timeout=6000')

Drupal to WordPress migration consulting

Any Drupal version · All content · Custom content types · SEO · Plugins

Migrating a site from Drupal to WordPress and need a specialist? Please contact me for a quotation. Whether you’re a media agency who needs a database expert or a site owner looking for advice, I’ll save you time and ensure accurate content exports.

Get a quote

Post-migration troubleshooting: Gateway timeout when enabling plugins

Here’s one that caught me out on a recent Drupal to WordPress migration. As is common with my projects, there were three parties involved: the client, an external development team and myself. The WordPress site was first built on the development team’s server, after which it was migrated to my local environment. When everything was ready for beta testing, we moved the site over to the client’s staging server on a newly activated account over at Kinsta. Eventually, we’d move it over to a live server, also hosted on Kinsta.

Diagram of Drupal to WordPress migration workflow for this project

After some initial tests on staging, I found that deactivating and reactivating plugins would cause the site to hang and show a ‘504 Gateway Time-out’ error. This happened when re-enabling some but not all plugins.

I initially suspected some misconfiguration at the hosting end because there were some hitches with the newly create account. At the outset, the account’s server had an issue which Kinsta support needed to fix. For convenience, we’d also made use of Kinsta’s free site migration service. This is where they’ll migrate an existing WordPress site into their environment. Though it would have been easy enough for me to do, we thought to give it a try. In hindsight, this was a bit of a mistake. The site migration service itself was fine but it did end up causing some confusion. First, a miscommunication in the migration request caused them to create a temporary domain we didn’t want. They helpfully solved this by giving us a second temporary domain. However, they’d also upgraded everything to PHP 7 in the process. All of these issues were possible suspects for the time-out error but turned out to be red-herrings.

It took some time to pinpoint the cause behind the Gateway Time-out error. I do have to say that Kinsta support were very responsive throughout the troubleshooting process. They eventually put a senior engineer on the case who found the problem. It turned out the problem wasn’t to do with Kinsta at all. There was a leftover setting from the original development team’s server. It was a valid format so didn’t cause an issue on either my local server or my staging server. However, it apparently can cause issues with plugins and did on the Kinsta environment.

What was the setting? The WordPress upload path directory was set to the development team’s server path e.g. /home/dev/public_html/sitename. Throughout the migration, I’d been doing a database search-and-replace looking for their development domain. Somehow, as the site moved from different servers, that server path string remained in the database, only to cause a problem when the site landed in the destination server on Kinsta.

I’m not sure if there would have been any way to have caught this problem earlier. It’s one of those obscure errors that are easy to overlook and take time to resolve. There’s also no practical way to do a database search-and-replace for every imaginable string. I’ll have to rack this one up to experience.

Post-migration troubleshooting: WordPress redirects to old site after updating database

If you’ve ever migrated a WordPress site, either to another URL or for a Drupal to WordPress migration project, you’ll know that WordPress stores the domain name in its database. This means you’ll have to jump through some hoops when moving WordPress to another environment. A critical step is to update the database to reflect the new domain. My favourite tool for this used to be the database search and replace script from interconnect/it. The script is PHP-based so runs on all environments that host WordPress. I now prefer WP-CLI’s wp search-replace command when on my own development environment, or for client hosting that supports it. Nevertheless, interconnect/it’s tool is still my fall-back option for clients of my Drupal to WordPress migration service since many use hosts that don’t offer command-line access.

In nearly all cases, updating the siteurl and home fields in the wp_options database table achieves the bare minimum to get the site working after migration. Running a search-and-replace across the WordPress database (in particular, the wp_posts table) will resolve broken links containing absolute URLs.

wp-admin still redirects to the old site after updating wp_options?

Once-in-a-while, I’ll encounter a migration project where wp-admin still redirects to the old site even after running through the obvious steps of:

  1. updating the database;
  2. clearing the browser cache;
  3. clearing the server cache.

It happens very rarely so I have yet to discover the cause. I suspect it’s something to do with sites that had a caching plugin installed, such as W3 Total Cache.

If you ever find yourself in this situation, the best workaround is to add the following two constants in wp-config.php:

define('WP_HOME', 'http://' . $_SERVER['SERVER_NAME']);
define('WP_SITEURL', WP_HOME . '/');

This isn’t a nice long-term solution but it should at least enable you to log in for some basic site administration. Once you’re able to log in to the WordPress Dashboard, disable any caching plugins after first clearing their cache.

Importing a WordPress database: How to fix the Unknown collation: ‘utf8mb4_unicode_ci’ error

If you do a lot of exporting and importing to different database servers, you’ll be familiar with the frustration of encountering MySQL import errors. Every so often when importing a WordPress dump file into a client’s database, I will encounter an Unknown collation error like the following:

Unknown collation: 'utf8mb4_unicode_ci'

Sometimes it will come up as:

Unknown collation: 'utf8mb4_unicode_520_ci'

This is caused by a difference in encoding types between the source and destination databases. It usually happens when you export from a newer MySQL database (MySQL 5.5.3 and above) which uses utf8mb4, then attempt to import into an older version using utf8. If you are importing from a dump file generated from a MySQL 5.6 database, you may get the utf8mb4_unicode_520_ci message. The 520 refers to MySQL’s use of Unicode Collation Algorithm 5.2.0. Unknown collation errors may also happen if you are trying to import a MariaDB database into MySQL. I tend to get unknown collation errors with my Rackspace Cloud accounts after Rackspace started offering MariaDB as a database option.

Ideally one would upgrade the older destination database but this isn’t always a realistic option. There are a number of discussion threads on the WordPress forum about what to do. Fortunately, many web hosting accounts have a phpMyAdmin interface which provides an easy work-around for the problem.

Format-specific options during a phpMyAdmin database export

  1. Log in to your database server using phpMyAdmin
  2. Make sure you select your database and go to the “Export” tab
  3. Select the “Custom” radio button
  4. Go the section “Format-specific options” and in the setting for “Database system or older MySQL server to maximize output compatibility with:” select MYSQL40.
  5. Scroll to the bottom and click GO.

phpMyAdmin format specific options to fix the Unknown collation: 'utf8mb4_unicode_ci' error

Other possible solutions include:

Since many of my WordPress database migrations are under my migration service, I don’t always have control over the client’s platform. The phpMyAdmin export format method is often the simplest solution.

Side-effects of a character encoding downgrade

You might be wondering about the purpose of encoding types and if there will be any side-effects of downgrading. Character encoding allows support for a set of characters, such as the Western alphabet, Asian scripts and non-alphanumeric symbols. Older utf8 databases support a smaller set of characters whereas utf8mb4 includes emojis, musical notation and Chinese Han characters. If you’ve ever exported a website from one CMS to another and found random characters scattered throughout the copy, it’s because of an incompatible character encoding.

Solving the unknown collation error as described here could mean you’ll end up with unsupported characters after your site migration. However, as with many of my Drupal to WordPress migration clients, in all likelihood you’ll be migrating from an older utf8 Drupal database to a newer utf8mb4-supported WordPress database. In this case, your old content will not have characters that will cause a problem after an encoding downgrade.

Post-migration steps: what to do after a Drupal to WordPress migration project

From time-to-time I get clients who ask me to only export the content to a WordPress database, after which they’ll complete the remaining setup themselves. If this applies to your project, you can use these migration notes to help get your new WordPress site running properly.

Import the database dump file

Please see these notes for importing the WordPress dump file.

Administrator credentials and email address

I will have changed your content management system (CMS) administrator password and email address to help with debugging. It’s important that you change these to your own as soon as possible.

Drupal and WordPress user passwords are encrypted so I won’t be able to view them. However, for your peace of mind, I recommend that you ask all your users to reset their passwords after your new WordPress site is live.

Server credentials

Please remember to change any database, (S)FTP, SSH server and control panel credentials you may have given me.

Migrating to a live server

I perform most Drupal to WordPress migrations on a development server. For help on how to move WordPress to your live server, please see: WordPress Codex: Moving WordPress.

Common errors after moving to a live server

Please see below for some common errors you may experience after migrating your new WordPress site to a new server.

Incorrect domain in URLs

WordPress stores domains in the database. If you performed the migration on a local or development server, there’s a good chance that the links will be incorrect after migrating to your live server. Use the Interconnect IT utility to run a search and replace on your database. This will also correct changed database prefixes.

More information can be found on the interconnect/it Search Replace DB page.

“You do not have sufficient permissions to access this page”

If you receive this error after logging in to your new WordPress installation, it’s possible that the database prefix on your new WordPress site is not set correctly. This may happen if you move your WordPress installation to a host that uses a different database prefix.

Try running one of the queries below. Replace wp_new_usermeta, oldprefix_ and newprefix_ as appropriate.

Option 1:

UPDATE wp_new_usermeta SET meta_key = REPLACE(meta_key,’oldprefix_’,’newprefix_’);

UPDATE wp_new_options SET option_name = REPLACE(option_name,’oldprefix_’,’newprefix_’);

Option 2:

update wp_new_usermeta set meta_key = ‘newprefix_usermeta’ where meta_key = ‘wp_capabilities’;

update wp_new_usermeta set meta_key = ‘newprefix_user_level’ where meta_key = ‘wp_user_level’;

update wp_new_usermeta set meta_key = ‘newprefix_autosave_draft_ids’ where meta_key = ‘wp_autosave_draft_ids’;

update wp_new_options set option_name = ‘newprefix_user_roles’ where option_name = ‘wp_user_roles’;

Please note that these queries may not work for you. Success depends on your specific setup.

For more information, please see the following pages:

Further help

I’ll be very happy to provide support you if have difficulties after migration. For a quotation, please contact me. I also offer customised hosting and maintenance packages. Please ask for details.

Handling Drupal terms during a Drupal to WordPress migration

When migrating Drupal terms into WordPress, it’s important to understand exactly what terms are and how the two systems handle categorising information.

A primer on Drupal taxonomies

One of Drupal’s most powerful features is its ability to organise content with taxonomies. Unfortunately, the taxonomy system is also notorious as one of the trickiest things about Drupal for beginners to understand. You can find a more detailed explanation here but essentially, a taxonomy is the practice and science of classifying things. In content management terms, you would mostly use taxonomies to organise and categorise articles or posts.

Taxonomies in Drupal uses the concept of vocabularies and terms. Terms are just a list of words that describe a particular type of content. They’re grouped together into vocabularies, which can be thought of as ‘containers’ for a set of terms. Vocabularies may be assigned to any content type. Drupal allows you to arrange the terms within a vocabulary using a parent-and-child hierarchical structure or they can be a flat list, with each term being on the same level as the others.

You can have many vocabularies in Drupal, each containing any number of terms. Vocabulary names must be unique and you cannot have duplicate term names within a vocabulary. It’s possible, however, to have the same term name appear in different vocabularies. Fig. 1 shows an example Drupal taxonomy with three vocabularies, Music, Movies and Books. The Movies and Books vocabularies both have the term Sci-Fi.

An example of Drupal vocabularies and terms
Fig 1: Drupal vocabularies and terms

For more information about the Drupal taxonomy system, please see Organizing content with taxonomies.

WordPress categories and tags

WordPress’ system for organising content is simpler. You have the option of categories–which can be hierarchical–and tags which are flat, or non-hierarchical. In general, categories in WordPress are used as a way of broadly organising posts and tags are used for more detailed descriptions.

Unlike Drupal, where you can have many containers in the form of vocabularies, a standard WordPress installation offers one container for categories and one for tags. Also as standard, categories and tags can only be assigned to the WordPress post content type. A WordPress developer can extend this by creating custom content types with their own categories and tags.

Fig. 2 shows show you’d organise the Music, Movies and Books categorisation in WordPress.

WordPress categories and tags
Fig. 2: WordPress categories and tags

Migrating Drupal terms as WordPress categories and tags

When running a Drupal to WordPress migration, we need to map Drupal’s more complex multi-vocabulary taxonomy system into the simpler WordPress model of categories and tags. How we do this depends on how you want to organise your new WordPress site. For example, we can:

  • convert Drupal vocabulary names into WordPress categories and Drupal term names into WordPress tags;
  • convert Drupal terms into WordPress categories and sub-categories;
  • vocabularies and their associated terms.

It’s all up to you and we figure this out during the requirements gathering stage of the project. For many sites, converting Drupal vocabulary names into WordPress categories and Drupal term names into WordPress tags, as shown in Fig. 3, seems to be the most sensible option. The important thing to know is that the migration may require us to ‘collapse’ or combine your taxonomies.

Merging Drupal and WordPress taxonomies
Fig 3: Merging Drupal taxonomies into WordPress

Since WordPress doesn’t support duplicate category or tag names, another thing to consider is how to handle any duplicate Drupal terms. Normally, the easiest solution is to append a unique number so that you can filter them out post-migration. We can do some clever merging and re-assigning of terms to posts but frankly, it’s probably not worth incurring the extra fees. Unless you have a great number of duplicates, you can probably do the job yourself quite easily via the WordPress Dashboard controls.

Organising your categories and tags in WordPress

Now that we know what’s involved in converting Drupal’s taxonomy over to WordPress, the next obvious question would be, “What’s the best way to structure categories and tags in WordPress?” While I cannot prescribe exactly how you should organise your site, I can point you to this excellent article so you can decide for yourself: Categories vs Tags – SEO Best Practices for Sorting your Content. Generally you should only have a few categories, maybe five or ten in total. Any more and they can become unwieldy and difficult to manage. These categories will reflect the main themes of your site. Tags can then further describe the details of each post and link specific topics together. You can have any number of tags.

The chances are that you probably want to avoid any drastic changes to the site structure when migrating from Drupal to WordPress. A simple mapping of vocabularies to categories and terms to tags is usually the closest equivalent in WordPress.

Why is the Drupal term_node table missing?

In a Drupal to WordPress migration post by Sam Michel, reader Jean-Philippe commented that why he couldn’t find the tables mentioned. I started composing my reply but for some reason the page wouldn’t let me post.

Rather than waste the time it took to compose the reply, I thought it would be good to post it here instead.


Hi Jean-Philippe,

This probably isn’t relevant to you anymore but I’m posting this for the benefit of anyone else who stumbles across your comment.

The tables names have changed in Drupal 7. ‘taxonomy_term_data’ and ‘taxonomy_term_hierarchy’ are all Drupal 7 tables. If you don’t see the tables mentioned in this post, it’s almost certainly because you don’t have Drupal 6 installed.

In Drupal 7, ‘term_node’ has been replaced with ‘taxonomy_index’.

I’ve started documenting the table mapping between Drupal and WordPress in a series of posts here: https://anothercoffee.net/drupal-to-wordpress-migration-posts-table-mapping/

Since I also used Scott Anderson’s SQL, anyone reading Sam Michel’s series might find it useful too. (Thanks to Sam and Scott!)

Drupal to WordPress migration notes

These Drupal to WordPress migration notes are intended for clients who are handling some aspects of the migration themselves. Users of the Drupal to WordPress Migration Tool or MySQL queries might also find information here to resolve some problems.

Admin account password and email address

Your content management system (CMS) administrator password and email address may have changed during the migration to help with debugging. Please update them as soon as possible.

Drupal and WordPress user passwords are encrypted and I do not have access to them in plaintext. However, for your peace of mind, I recommend that you also ask all your users to reset their passwords.

Server credentials

Please remember to change any database, (S)FTP, SSH server and control panel credentials you may have given me.

Working tables

During the migration process, I may create some working tables to hold temporary data. My naming convention for the working tables are as follows:

  • acc_ prefix: these are working tables created to help with migrating data.
  • backup_ prefix: these are backups of existing tables prior to migration, for example from a previous installation of your CMS. These will not be altered during the migration process.
  • _copy postfix: duplicates of WordPress tables copied for debugging will have a _copy postfix. These are different from the backup_ tables in that they may have been manually altered.

These working tables are not used by WordPress so you may safely delete them. However, it’s advisable to keep them for a short while as they may be useful in case we need to debug any issues that crop up.

Migrating to a live server

Most Drupal to WordPress migrations are performed on a test or development server. For help on how to move WordPress to your live server, please see: WordPress Codex: Moving WordPress.

Troubleshooting common errors after a site migration

Please see below for some common problems you may experience after migrating your Drupal content to a new WordPress site.

Incorrect domain in URLs

WordPress stores domains in the database. If you performed the migration on a local or development server, there’s a good chance that the links will be incorrect after migrating to your live server. Use the Interconnect IT utility to run a search and replace on your database. This will also correct changed database prefixes.

More information can be found on the interconnect/it Search Replace DB page.

“Sorry, you are not allowed to access this page”

If you try to log in via wp-admin and receive this error, you may have overwritten the administrator user’s wp_capabilities or wp_user_level.

Set the correct meta_value using the following SQL:

UPDATE wp_usermeta 
    SET meta_value = 'a:1:{s:13:"administrator";s:1:"1";}'
    WHERE user_id = 1 AND meta_key = 'wp_capabilities';

UPDATE wp_usermeta 
    SET meta_value = '10'
    WHERE user_id  = 1 AND meta_key = 'wp_user_level';

Remember to use the appropriate the user_id.

“You do not have sufficient permissions to access this page”

If you receive this error after logging in to your new WordPress installation, it’s possible that the database prefix on your new WordPress site is not set correctly. This may happen if you move your WordPress installation to a host that uses a different database prefix.

Try running one of the queries below. Replace wp_new_usermeta, oldprefix_ and newprefix_ as appropriate.

Option 1:

UPDATE wp_new_usermeta SET meta_key = REPLACE(meta_key,’oldprefix_’,’newprefix_’);

UPDATE wp_new_options SET option_name = REPLACE(option_name,’oldprefix_’,’newprefix_’);

Option 2:

update wp_new_usermeta set meta_key = ‘newprefix_usermeta’ where meta_key = ‘wp_capabilities’;

update wp_new_usermeta set meta_key = ‘newprefix_user_level’ where meta_key = ‘wp_user_level’;

update wp_new_usermeta set meta_key = ‘newprefix_autosave_draft_ids’ where meta_key = ‘wp_autosave_draft_ids’;

update wp_new_options set option_name = ‘newprefix_user_roles’ where option_name = ‘wp_user_roles’;

Please note that these queries may not work for you. Success depends on your specific setup.

For more information, please see the following pages:

“Unable to establish database connection”

The database credentials are correct but you see an “Unable to establish database connection” error. Check that wp_options table is not empty.

Allowed memory size exhausted

  1. Increase php.ini memory size
  2. Increase WP settings memory limit with:
    define(‘WP_MEMORY_LIMIT’, ‘128M’);

Post migrated but navigating to post shows blank page

The post is visible in the dashboard but viewing it displays a blank (but themed) page. Manually saving it on the dashboard makes it appear.

It’s possible that the problem posts need to be assigned to a category.

Post migrated but navigating to post shows ‘Not found’ error

The post is visible in the dashboard but viewing it displays a ‘not found’ error. Manually saving it on the dashboard makes it appear.

  1. Check that the url contains valid characters for a WordPress slug.
  2. Check that .htaccess is enabled in your Apache configuration

Link to author 404

Posts exist but link to the author’s post listing page is broken.

Check user_nicename in wp_users WordPress table. Make sure the nicename doesn’t contain invalid characters such as spaces, periods.

Dashboard controls not visible after logging in

If you are able to log in as an administrator user but do not see the Dashboard controls, check your table prefixes. If the table prefixes changed during the migration, you may have forgotten to update the options and usermeta tables.

Check where the old prefixes have been set:

SELECT * FROM `wpnew_options` WHERE `option_name` LIKE '%wp_%';
SELECT * FROM `wpnew_usermeta` WHERE `meta_key` LIKE '%wp_%';

Updated the prefixes. For example:

UPDATE `wpnew_options` SET `option_name` = 'wpnew_user_roles' WHERE `option_name` = 'wp_user_roles';
UPDATE `wpnew_usermeta` SET `meta_key` = 'wpnew_capabilities' WHERE `meta_key` = 'wp_capabilities';
UPDATE `wpnew_usermeta` SET `meta_key` = 'wpnew_user_level' WHERE `meta_key` = 'wp_user_level';

UPDATE `wpnew_usermeta` SET `meta_key` = 'wpnew_user-settings-time' WHERE `meta_key` = 'wp_user-settings-time';
UPDATE `wpnew_usermeta` SET `meta_key` = 'wpnew_user-settings' WHERE `meta_key` = 'wp_user-settings';

Further help

We’ll be very happy to provide support you if have difficulties after migration. For a quotation, please contact us. We also offer customised hosting and maintenance packages. Please ask for details.