12.1. Access rights to data in shares#

Access permissions to files are managed in UCS using users and groups. All the file servers in the UCS domain access identical user and group data via the LDAP directory.

Three access rights are differentiated per file:

  • read

  • write

  • execute

Three access rights also apply per directory: read and write are the same; the execute permission here refers to the permission to enter a directory.

Each file/directory is owned by a user and a group. The three permission outlined above can be applied to the user owner, the owner group and all others.

setuid

If the setuid option is set for an executable file, it can be run by users with the privileges of the owner of the file.

setgid

If the setgid option is set for a directory, files saved there inherit the directory’s owner group. If further directories are created, they also inherit the option.

sticky bit

If the sticky bit option is enabled for a directory, files in this directory can only be deleted by the owner of the file or the root user.

Access control lists allow even more complex permission models. The configuration of ACLs is described in SDB 1042.

In the Unix permission model - and thus under UCS - write permission is not sufficient to change the permissions of a file. This is limited to the owner/owner group of a file. In contrast, under Microsoft Windows all users with write permissions also have the permission to change the permissions. This scheme can be adjusted for CIFS shares (see Management of shares via UMC module).

Only initial users and access permissions are assigned when a directory share is created. If the directory already exists, the permissions of the existing directory are adjusted.

Changes to the permissions of a shared directory performed directly in the file system are not forwarded to the LDAP directory. If the permissions/owners are edited with the UMC module Shares, the changes in the file system are overwritten. Settings to the root directory of a file share should thus only be set and edited with the UMC module. Additional adjustment of the access permissions of the subordinate directories are then performed via the accessing clients, e.g., via Windows Explorer, or directly via command line commands on the file server.

The homes share plays a special role within Samba. This share is used for sharing the home directories of the users. This share is automatically converted to the user’s home directory. Samba therefore ignores the rights assigned to the share, and uses the rights of the respective home directory instead.