I use COPS with a Kobo e-reader and I can't download any books
You have to enable URL rewriting ($config['cops_use_url_rewriting']) to make it work.
How do I protect my COPS library with user/password
Each time I install a new version of COPS, all my settings are lost
You may have modified config_default.php and you shouldn't, all your settings should be in config_local.php which is never overwritten.
With a specific device, I only see a gray screen. On my favourite desktop browser everything work as expected
A workaround has been added for Kindles and Sony PRS-TX. Cybook's browser don't handle HTML5 at all so the last working version of COPS is 0.4.0.
In case your device is not listed above, please open an issue with the user agent of your device (check with http://whatsmyua.com/).
I've password protected my COPS and I can't download books with my Android device
There's an old bug with Android about that. Long story short, you'll have to use an OPDS client to download your books (FBReaderJ for example).
I've password protected my COPS and my Kobo can't access it anymore
Kobo's browser don't support HTTP basic auth but you can use login.html as a workaround.
I've password protected my COPS and my Sony PRS-TX can't download any ebooks and I can't see any covers
Sony's browser don't like authentication while downloading books. You can check at the bottom of .htaccess for a workaround.
Please note that Aldiko also has the same problem so please always try to remove authentication check before filing a bug.
How do I use search in the HTML catalog
You have to click on the cog wheel (top right).
COPS seems to work fine, I can download most of my ebooks but some fails
It may be because the file path stored on Calibre library is different from the actual path on disk (often a case difference). You can check your library with checkconfig.php?full=1.
COPS seems to be working correctly (I can see covers and book information) but I can't download books
9 times out of 10, it's due to this setting in config_local.php :
$config['cops_use_url_rewriting'] = "1";
If you enabled URL rewriting, you'll have to make sure your webserver can do it. If you don't know, just remove this line and you'll be able to download books.
You can also check this setting :
/* * SPECIFIC TO NGINX * The internal directory set in nginx config file * Leave empty if you don't know what you're doing */ $config['calibre_internal_directory'] = '';
As stated in the comment : it should only be filled when using Nginx. If you don't know if you're using Nginx or not then you're probably not running it so leave it empty.
After update my Synology's firmware to DSM 5, COPS is not working anymore
Starting with DSM5 Synology stopped providing mod_auth which was used in COPS authentication system. X-SendFile is also not working anymore and I still have doubts about URL Rewriting.
You can try checking the "mssql" checkbox or if it doesn't work there is the hard way