Permanent user permission

Question

I have a folder in which periodically files are stored with 755 permission by the root user. I'd like the user 'www-data' to have full permission to all of the files. I used chown, but when a new file is added by the root user I have to re-do it.

The files are added through a BTsync daemon that's run by the root user. I couldn't figure out how to run it as www-data.

Is there a way to give the www-data user permanent access to the folder?

Answer 1

You may not be able to change the user ownership of every new file created in a particular folder to www-data. But you can change the group ownership of every new file created in a particular folder to www-data by setting the setgid flag of the directory.

nifty:~# whoami
root
nifty:~# mkdir foo
nifty:~# chown www-data:www-data foo
nifty:~# chmod g+s foo
nifty:~# ls -l
total 4
drwxr-sr-x 2 www-data www-data 4096 Nov 17 21:49 foo
nifty:~# touch foo/hi.txt
nifty:~# ls -l foo
total 0
-rw-r--r-- 1 root www-data 0 Nov 17 21:52 hi.txt

Note that you cannot change the user ownership of the new files created in a particular folder automatically because setting the setuid flag on a directory has no effect.

nifty:~# mkdir bar
nifty:~# chown www-data:www-data bar
nifty:~# chmod a+s bar
nifty:~# ls -l
total 8
drwsr-sr-x 2 www-data www-data 4096 Nov 17 21:54 bar
drwxr-sr-x 2 www-data www-data 4096 Nov 17 21:52 foo
nifty:~# touch bar/hi.txt
nifty:~# ls -l bar
total 0
-rw-r--r-- 1 root www-data 0 Nov 17 21:54 hi.txt