Problem understanding file permissions

Question

I have a problem understanding some aspects of file permissions. The situation is this:

I created a directory as /to using sudo and then changed it's permissions to drwxrwsr-x. I also changed the group for the directory to "xxx" which exists on my system. I am a member in good standing of group "xxx". My understanding is that I should be able to create files and directories in /to since I am a member of group "xxx".

However when I run the following command I get permission denied when trying to create each file and directory in /to.

cp -r from/* /to

What am I not understanding about this situation? I can obviously fix this particular instance with sudo or by changing the owner, but I want to understand the principles.

Command output

jgossage@Hector:~$ cp -r Downloads/* /Downloads
cp: cannot create directory /Downloads/Eclipse': Permission denied
cp: cannot create regular file /Downloads/google-chrome-stable_current_amd64.deb':
Permission denied
cp: cannot create directory /Downloads/Kindle': Permission denied
cp: cannot create directory /Downloads/WindowsDlls': Permission denied
#Target directory information
jgossage@Hector:~$ ls -al /Downloads
total 8
drwxrwsr-x 2 root admins 4096 Feb 13 07:16 .
drwxr-xr-x 28 root root 4096 Feb 14 08:23 ..
jgossage@Hector:~$

Answer 1

Looking at the permissions you set I don't think you have granted "others" permissions to write to the directory. Looking at the permissions you've granted

drwxrwsr-x

I'm pretty sure that breaks down as:

type: d
owner: rwx (Read/Write/Execute)
group: rws (Read/Write/Special)
all/others: r-x (Read and Execute)

Since the folder was created as root (sudo) only the root user has access to write to the folder (although as a user you can read the contents of the directory).

I think to fix the problem you should be able to run:

sudo chmod o+w /to

Naturally replacing /to with the real folder name/path. This will give ALL users write access to the folder which is probably not ideal. Alternatively you can take ownership of the folder (and all files within the folder):

sudo chown -R jgossage /to

Again replacing /to with the real folder name/path. This should keep the directory permissions the same (drwxrwsr-x) which would mean that the owner would have read/write/execute permissions but other users would only have read and execute permissions.