-- Draft 4.5.3
When a User edits a file, Joomla! changes its status to, "Checked Out". Thereafter the file is locked and only the User who has "checked it out" has permission to work with it. This is a security feature that prevents two Users from editing a document at the same time, thus preventing loss of data upon saving.
An Item remains 'Checked Out' until the User clicks 'Save' or 'Cancel' while editing the Item, at which time the Item is "Checked In". However, if there's a connection error (the user presses the 'Back' icon in his/her browser, or the User chooses another menu item without saving or canceling the work in progress) the Item remains 'Checked Out'. This means no one can edit it. This is usually reported or experienced as Users being unable to edit or access items, and can be verified by looking at the column labeled "Checked Out" in the various Managers.
Joomla! has a protocol, called "Checkin" that allows an administrator to unlock all or specific Items that are currently "Checked Out". This can be done on an individual base in each concerned Manager, but also on a multiple base through this feature.
To perform the "Check In", select System > Checkin Manager from the Administrator Menubar. After performing the "Check In", Joomla! returns a list showing how many items, and from which tables, are still checked out..
WARNING: Be very careful in doing this as anyone who is editing a document at that very moment can have his or her work lost.
Checkin: Click this icon to checkin the items chosen in the table.