Fonts are not just files, but rather system plug-ins, similar in ways to an extension or add-on application. When added and activated, they load into memory and are associated to programs by the system so programs can make use of them and show information about them.
As a result, should a font be damaged, or perhaps conflict with another font, then not only might it lead to improper characters being used, or alignments being off in documents, but also crashes and hangs for programs that access these fonts.
Font conflicts occur when two fonts of different type faces (or perhaps even more subtle difference) have the same internal name. For instance, the system’s internal font Monaco has a specific look and character layout for use with the system, and many programs rely on this font in this manner. However, if a font from a third-party with the name “Monaco,” or perhaps a modified version of Monaco is installed, then the system will identify two of the same type and not know which to use. In these cases, the system or application will use the first one it identifies, which may be the improper one and cause visual conflicts.
Font conflicts and damaged fonts can cause a document to display garbled text (click image for larger view).
In most cases, font conflicts occur because someone installed a duplicate of the exact same font, so one resides in a system library such as the system’s font folder (Macintosh HD > System > Library > Fonts), or the global font folder (Macintosh HD > Library > Fonts). These two library folders contain settings and resources that apply to the entire system and all users. The system folder contains core fonts that Apple provides and which are required in unaltered states for OS X to run. These take precedence over other fonts; however, a program can install a font in the global font folder that is the same as one in the system’s font folder, and result in a font conflict.
Similarly, a user can install a font library for their uses, which may contain duplicates of fonts already in the system or global fonts folder, and again result in a font conflict.
In the case of damaged fonts, the system may attempt to load them and either not be able to and result in a hang or crash, or will load them and you will see corrupt symbols appear instead of the desired font face. At other times, the symptoms may not be so apparent, such as a fault with only specific characters that cause problems when they are displayed.
For older and incompatible fonts, the system will usually just not load them; however, there may be instances where it tries and results in a persistent error, slow loading, or some other odd behavior either with the system or with the specific program you are using, that can frustrate your workflow.
Expanding the font with the error shows the only problem here is a duplicated font file. This is a relatively minor issue, especially if the font is an unmodified duplicate (click image for larger view).
There are various ways to troubleshoot and repair font problems in OS X. This procedure essentially involves identifying any problematic fonts, and then removing, disabling, or replacing them.
Note that for any font-related procedure, you keep track of what you do and where you move or otherwise place fonts, to be able to undo any changes you make. Also keep in mind that any changes you make outside of your home folder will potentially affect other users on your system.
1. Font Book
If you use a third-party font manager for your fonts, then be sure it is updated and then open it to manage your font collection. Depending on the program you use, there may be routines you can run to check your various fonts for conflicts and other errors. In Apple’s Font Book, you can click the All Fonts collection, followed by clicking a font and then pressing Command-A to select all fonts on the system. Then choose “Validate Fonts” from the File menu, and the program will check for conflicts, compatibility, and damage to your fonts.
While you can usually get away with minor errors found in the font validation routine (noted by a yellow circle with an exclamation point in it), you might want to investigate the cause for this problem.
If you see any errors that are colored red, then this indicates a problem that will likely cause a disruption to programs and services that use this font, and you should consider disabling, removing, or reinstalling the font.
Right-clicking a font in Font Book gives you options to manage it (click image for larger view).
In all cases, from the validation window you can click the checkbox next to a font to select it, and then click “Remove Checked” to delete the selected fonts. Alternatively, you can identify the fonts and close the validation window, followed by managing them in the Font book window in the following ways:
Select all fonts and right-click them, followed by choosing “Resolve Duplicates.” This will disable any global fonts that are in conflict with those in your home folder, and keep the ones in your home folder active. This setting is for your account only, so global fonts will still be active for other users.
You can select a font set by holding the Command key and clicking individual fonts, or by creating a new collection (in the File menu) and dragging fonts to this collection. With your set created, you can right-click it and choose the option to disable the set. This will turn off these fonts for your account, but keep them installed for other accounts to use. Note that this can be done for an individually selected font, but it may be easier to manage a number of fonts through a collection.
The final option is to select a font, selection of fonts, or a collection, and then again right-click it but this time choose the option to remove the fonts. This will delete them and make them unavailable to any user account in the system.
2. Manual management
While the font book application and similar font managers might be preferentially used for dealing with font problems, you can also approach this manually. As mentioned above, fonts in OS X are in the following three folders, though the last two are the only ones you should modify:
Macintosh HD > System > Library > Fonts Macintosh HD > Library > Fonts
Macintosh HD > Users > username > Library > Fonts