On Wednesday, February 20, 2019 9:17:34 AM CST Chris Schanzle wrote:
> On 2/16/19 12:14 PM, Bill Gee wrote:
> > ...After the usermod programs ran, I then did a "find -uid=500" with an
> > exec option to change ownership. Repeat for changing GID. It found a few
> > dozen files that were not in my home directory.
> >
> > On the server I ran the two "find" commands against the entire file system.
> > It took about half an hour to run. No surprise there as it was finding
> > and changing several hundred thousand files. I ran the uid change in one
> > terminal and the gid change in another. Between the two of them they
> > consumed about 90% on both processor cores.
>
> Hi Bill,
>
> Just sharing some wisdom/experience. Too bad it's after the bulk of your
> work. :-)
>
> It should not have been consuming much cpu. This is an I/O-based activity.
>
> My guess is you used something like
>
> find -uid=500 -exec chown 1000 {} \;
>
> This will start a chown process for each file, changing only one file at a
> time. That's a lot of work the system has to do for each file! But you
> probably know chown (and similar utilities) can take multiple file arguments,
> and 'find' can help you take advantage grouping many arguments with the '+'
> operator to -exec:
>
> find -uid=500 -exec chown 1000 {} +
>
> And you could combine the bulk of your I/O work of chgrp-ing for all of your
> files at the same time by using 'chown 1000:1000'.
>
> You might want to check your symlinks ('find -type l -ls'). You may have
> changed the ownership of what they point to rather than the link itself,
> precisely what the chown -h (--no-dereference) option is good for. Don't
> forget to revisit what the permissions should be on the link targets. Bad
> things would happen if the user had a symlink to /etc/passwd and/or
> /etc/shadow in their home directory!
>
> I also like to use -xdev to avoid traversing into any unexpected filesystems.
> So I end up with:
>
> find /somedir -xdev -uid=500 -exec chown -h newID:newGroup {} +
>
> Hope that helps for the next time or someone else!
>
> [This is off the top of my head, so beware of any mistakes...these commands
> have significant consequences.]
>
> Best regards,
>
> Chris Schanzle
>
>
Thanks Chris and Simon -
I was not concerned about CPU usage while running thousands of instances of
chown and chgrp. It was expected, and this server does not handle any user
except me. I will keep that '+' operator in mind for the next time I need it.
It will not be needed often, but when needed it will be very useful.
I ran chown and chgrp separately because there are some files that are owned by
me but have other groups - and a few which I do not own but are in my group.
Using "chown user:group" to change both would have overridden those few odd
files.
I checked for symlinks and did not find any that were changed by mistake.
That's one bullet I seem to have dodged by luck.
Bill Gee
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