Chmod – Recursive Permission on Thousands of Files

chmodpermissionsrecursive

This is a more general question about 'chmoding' recursively.

I have this script which at some point needs to change the permissions recursively in a folder which has a few hundred thousand files.
There are new files added in that folder every day, but the ones that are already there have the permissions already set and they don't change.

My question is… when I call 

chmod 775 . -R

does it try to set the permission for the files that already have the right permissions set, or only for the new files that don't have the right permissions?

It seems to always take ages to get past this command in the script, even though the 'new' files are only a few thousand and it should do their permissions fairly quickly.

I've looked at the man page for chmod, but it doesn't seem to mention anything on this case.

If chmod doesn't check for permissions beforehand, should I start looking at combining 'find' with 'chmod'?

Best Answer

chmod might or might not change the permissions of files that are already set to what you want, but if not, it would still need to check them to see what their current permissions are[0]. With hundreds of thousands of files, I don't think it would matter either way; the time is most likely being spent by the tools stating every file.

You can try using find to either check for files newer than the last run or files that need chmod to be run, but I don't think you'll get much speed improvement.

If possible for your script, you might be able to get the new files put into a separate directory first, as a "holding" area. Then you can chmod THAT directory (which only has new files), and mv them in with the rest. That should be substantially faster, but unfortunately won't work for every application.

[0] Even if it does try to set the permission of files that don't need any changes, the underlying filesystem probably won't do anything with the request, because it's unnecessary.

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