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4.3.2. File Permissions
File Permissions define the explicit rights a computer or user has to a particular directory, file, or set of files. Such permissions may be defined by editing the /etc/samba/smb.conf file and specifying the explicit permissions of a defined file share.
For example, if you have defined a Samba share called share and wish to give read-only permissions to the group of users known as qa, but wanted to allow writing to the share by the group called sysadmin and the user named vincent, then you could edit the /etc/samba/smb.conf file, and add the following entries under the [share] entry:
read list = @qa
write list = @sysadmin, vincent
Another possible Samba permission is to declare administrative permissions to a particular shared resource. Users having administrative permissions may read, write, or modify any information contained in the resource the user has been given explicit administrative permissions to.
For example, if you wanted to give the user melissa administrative permissions to the share example, you would edit the /etc/samba/smb.conf file, and add the following line under the [share] entry:
admin users = melissa
After editing /etc/samba/smb.conf, restart Samba for the changes to take effect:
sudo systemctl restart smbd.service nmbd.service
For the read list and write list to work the Samba security mode must not be set to security = share
Now that Samba has been configured to limit which groups have access to the shared directory, the filesystem permissions need to be updated.
Traditional Linux file permissions do not map well to Windows NT Access Control Lists (ACLs). Fortunately POSIX ACLs are available on Ubuntu servers providing more fine grained control. For example, to enable ACLs on /srv an EXT3 filesystem, edit /etc/fstab adding the acl option:
UUID=66bcdd2e-8861-4fb0-b7e4-e61c569fe17d /srv ext3 noatime,relatime,acl 0 1
Then remount the partition:
sudo mount -v -o remount /srv
The above example assumes /srv on a separate partition. If /srv, or wherever you have configured your share path, is part of the / partition a reboot may be required.
To match the Samba configuration above the sysadmin group will be given read, write, and execute permissions to /srv/samba/share, the qa group will be given read and execute permissions, and the files will be owned by the username melissa. Enter the following in a terminal:
sudo chown -R melissa /srv/samba/share/ sudo chgrp -R sysadmin /srv/samba/share/
sudo setfacl -R -m g:qa:rx /srv/samba/share/
The setfacl command above gives execute permissions to all files in the /srv/samba/share
directory, which you may or may not want.
Now from a Windows client you should notice the new file permissions are implemented. See the acl and setfacl man pages for more information on POSIX ACLs.