BEFORE YOU DO ANYTHING TO THE REGISTRY, ALWAYS TAKE A BACKUP.
See the "tips" section for a link to ERUNT, a handy backup tool. Taking a backup of the registry is an essential part of maintaining it, as it will allow you to undo any negative changes you make. It is very easy to mess up the registry, and unfortunately if you don't have a backup, exceedingly difficult to fix. Taking a backup will allow you to fix any mistakes and save yourself a lot of effort.
Here are some posts by Jamin4u that may help you set ERUNT up (thanks for the links)
Running ERUNT on Vista
Just because something comes up on the REGCleaner section DOES NOT mean that you SHOULD remove it.
I'm only here because I heard cleaning the registry makes the computer just like new, is that true?
This is actually an issue of much debate, but the general consensus seems to be that unless you remove thousands and thousands of keys from the registry, its not significantly smaller to be any more efficient at what it does. Thats not to say however, that a tiny performance gain wont be seen at all.. again, this is on the fence and noone seems to really agree on whether or not it does.
Is the registry cleaner safe to use?
It could be said that it is indeed safe to use, but unfortunately ALL registry cleaners have some element of danger behind them. While CCleaner does use methods of scanning that are safer than most cleaners, the best method of cleaning would probably be to manually pick through all the keys detected to make sure that they are indeed safe to clean, as well as taking a backup (and remembering where it is and what its named) so that if you fail to notice some important key, it can easily be restored by double clicking the backup.
I don't know what the registry is, should I still use this tool?
Probably not. The windows registry is essentially the central database used to store the settings for users, programs, and the system. Its not something that can be tampered with without at least some knowledge of what you're doing. This isn't to say the registry cleaner will definitely break your computer, and in most cases it is safe to remove the majority of keys CCleaner detects, however if you really have no clue what you're doing, and/or how to undo what you've done, I really wouldn't recommend you use this feature.
*For more information on what the registry is, and what it does, try the Wikipedia Article
How do I run the registry cleaner?
This is covered by the piriform documentation, and can be found: here!
Does cleaning the registry do anything?
Yes, it can and most likely will improve performance of your computer. This is not to say you should remove all the keys you see to gain maximum performance (see quote by Nergal at the beginning of the post)
The registry tool hangs at x%, why is this
First: give it some time. If your computer is especially slow, this can be the issue. The registry scan can be slow on some machines, but give it a few minutes or if its not pressing, try letting it run while you sleep. If it still hasn't finished over night, then theres a problem.
In that case, try un-ticking every box, then scanning each one one at a time. If you can scan them all individually, then good. You probably have many invalid keys and just need to clean it. If you find you can't scan a certain selection, try posting a query (see tips)
Help! I used the registry cleaner and now something doesn't work!
First and foremost, if you can boot into windows at all (this includes safe mode,) try restoring the backup you should have taken when cleaning the registry. After merging the registry keys you cleaned, and rebooting the computer doesn't work, its likely not caused by ccleaner, and you should try a System Restore. If worst comes to worst, try using a windows recovery disc or the windows recovery console to fix your system files without data loss, thus allowing you to rebuild whatever configuration was lost.
The cleaner keeps detecting a certain key, and its not removed when I fix the issue.
There are several reasons this could be.
1) The key is locked. CCleaner can't remove "locked" keys, and they'll have to be manually fixed (advanced users would want to manually navigate to the key via regedit and fix it them selves, novices may just want to leave the key alone if its not hurting anything.)
2) Your user account doesn't have the permissions to remove the key. CCleaner can usually remove everything you need it to, but in some cases a key will require Administrator privileges. If your account doesn't have this, either log onto an account that does or contact someone who can. Else, leave the key alone.
If neither of those apply, see this link or this forum post
Does cleaning Missing Shared DDL's delete any files?!
No, it only removes registry keys pointing to files detected as no longer existing. Again, this doesn't make it 100% safe, but you wont be removing any files if thats your concern.
I keep cleaning a "missing shared DLL" key, but it keeps returning, even when I remove it via Regedit
Its likely these DLL references are being re-created every time they are deleted and you should just leave them alone. However if it means that much to you, try looking up the DLL name to see what program it is associated with to confirm whether or not you really need it.
CCleaner removed the file association for *.*, how do I get it back?
Try these helpful downloads, they contain .Reg files that can be merged with the registry to return it to its default.
(Thank you HazelNut for those links)
Very complicated instructions you all found! The easiest way to restore / reset a file association is with the ASSOC command.
For example, to restore the .exe file association you open a command prompt, then enterassoc .exe=exefileVery simple, and it doesn't need any manual fiddling with the registry.
I think this is safe to remove?
My own opinion: If in doubt, don't.
Thinking is the same as not knowing, and it'd be best not to remove something that looks like it may be important.
Does CCleaner clean the registry, or repair it? Is there a difference?
It can be said that CCleaner cleans the registry. The difference between the two can be found in a discussion on this thread.
TL;DR of that thread;
Cleaning - Deletes unused / invalid keys
Repairs - updates unused / invalid keys with proper information to make them useful.
Does CCleaner defragment my registry? What is that anyway?
No, at least not yet, it may be in development though. Perhaps not at the same time, you'd have to ask an Administrator !
Defragmenting the registry is similar to defragmenting your hard drive. It removes gaps in the registry to allow the disc to read the registry files contiguously thus allowing faster access to them.
The registry tool reports "no problems detected," what does this mean?
It means CCleaner didn't detect any issues that it deemed worthy of cleaning. This isnt to say your registry is in perfect condition, but unless your an advanced user its best not to pursue it any further than CCleaner.
Is it possible to have the registry cleaner run and fix all issues autonomously?
No, and even if it were, why would you risk critical damage to your computer just so you didn't have to go through the hassle of sorting keys yourself? This would be a dangerous implementation in the program as it could hinder system stability (however unlikely) and will probably never be added.
How long do I have to keep the backups for? They're cluttering up the folder they're in!
I'd honestly recommend forever, and put them in a subfolder like My Documents\CCleaner Backups\ to keep things tidy. Keeping all your backups allows you to restore anything that may have been accidentally removed. If you're really pressed for space or you're 150% certain you dont need a certain backup, I'd recommend waiting about a week, maybe 2 before deleting anything, because once you delete those backups, they're gone (Unless you use a recovery tool like Recuva, which probably wont be possible if you delete some critical keys.)
Can I use registry cleaners other than CCleaner?
Yes, but support for them isnt given here, and you'll have to find them on your own. However; I cannot stress enough how important it is that you actually know what you're doing before playing with these tools. Also, when using them, be sure to take proper restore points and backups so you can undo any changes.
My other registry cleaner finds way more problems, even after using CCleaners, why is this?
CCleaner uses a lighter method of cleaning and is "safer" (term used lightly) than ones that dive into the deepest parts of the registry. You wont get support for those programs on this forum though.
I find ccleaner is a very gentle and safe reg cleaner, sometimes others can go too deep.
I'm an advanced user, can you recommend some registry defragmenters?
This one is somewhat less risky, but often the registry's fragmentation rate is negligible. However if you really want to try, heres a few programs.
*This feature will never be included in CCleaner (most likely) as it does nothing for your performance.
Auslogic's Registry Defrag
Free registry defrag
*ALWAYS backup any changes you make to the registry
The registry is important, and your best friend. Don't hurt your best friend! you can use ERUNT to back everything up
*Before posting USE THE SEARCH BUTTON.
It can be found here and above and will often turn up results similar to your problem. Many times an issue can be resolved without ever needing to post.
*If you must post a query about the registry, make it as comprehensive as possible. State your operation system, CCleaner version and any involved keys (right click -> save to text file)
An in depth query will result in more accurate and timely responses from the community. Help us help you. Proper typing is a bonus too, remember this is an English forum!
*When posting, make sure you start a new topic. Often times old issues wont be looked at and if they are, you'll likely be told to start your own post.
*If you didn't find an answer in this, post a comment and I'll try to add it.
Always here to help.
I'll update this as needed/requested.