Linker custom fields not visible after upgrade to JIRA 6
In the old version of JIRA, there was JIRA Linker plugin that was used to add custom fields to store links. If an instance with these custom fields is upgraded to JIRA 6.x then these custom fields are no longer visible after the upgrade.
This plugin has been removed from JIRA 5.0 and the functionality has been added to core JIRA. However, there is no custom field type key : 'com.atlassian.jira.plugin.linker:linker' on the new JIRA versions. Hence JIRA is not able to show these fields on the UI.
Here are the steps you can take in order to convert the Linker custom fields to Url custom fields.
Run the following query in the database :
update customfield set customfieldtypekey='com.atlassian.jira.plugin.system.customfieldtypes:url', customfieldsearcherkey='com.atlassian.jira.plugin.system.customfieldtypes:exacttextsearcher' where customfieldtypekey='com.atlassian.jira.plugin.linker:linker';
Notice that the Linker custom fields are now working again.