Setting up a Share Using POSIX ACLs

Introduction

Samba enables you to create file shares using POSIX access control lists (ACL) on:

• Domain members
• NT4 PDC and BDCs
• Standalone hosts

On a Samba Active Directory (AD) domain controller (DC), extended ACL support is enabled globally and thus shares using POSIX ACLs are not supported. Samba AD DCs only support shares using Windows ACLs.

As an alternative to POSIX ACLs, you can set up shares using Windows ACLs. For details, see Setting up a Samba Share Using Windows ACLs.

Preparing the Host

Before you are able to create a share, set up Samba. For details, see:

• Setting up Samba as a Domain Member
• Setting up Samba as an NT4 PDC (Quick Start)
• Setting up Samba as an NT4 BDC
• Setting up Samba as a Standalone Server

Making Files Executeable

Using the default setting, users are only able to execute files, such as *.exe and *.bat, on a Samba share if they have the POSIX x-bit set. For example, the following file is executeable for the root user and members of the Domain Users group:

-rwxr-x--- 1 root "Domain Users" 133160 1. Jan 00:00 /srv/samba/Demo/example.exe

In some scenarios it is necessary to enable users to execute all files on a share, regardless if the x-bit is set. To enable, set in the [global] section of your smb.conf:

acl allow execute always = yes

Adding a New Share

To share the /srv/samba/Demo/ folder using the Demo share name:

• Create the folder:

# mkdir -p /srv/samba/Demo/

• Add the [Demo] share definition to your smb.conf file:

[Demo]
       path = /srv/samba/Demo/
       read only = no

These are the minimum parameters required to set up a writeable share. Optionally, you can set share permissions. For details, see Setting Share Permissions.

• Reload the Samba configuration:

# smbcontrol all reload-config

Setting POSIX ACLs on a Samba Share

To control access to folders on a share, use the operating system-specific tools. For example, to set the owner of the /srv/samba/Demo/Example/ directory to root, grant read and write permissions to the owner and the Domain User group, and deny access to all other users, enter:

# chmod 2770 /srv/samba/Demo/Example/
# chown root:"Demo Group" /srv/samba/Demo/Example/

Setting the SGID bit (2770) automatically inherits the directory's group to all new files and directories created, instead setting it to the user's primary group.

For further details about the permissions, see the chmod(1) and chown(1) man page.

Setting Share Permissions

Optional: Samba enables you to set permissions on each share which are validated when a user connects.

Access to the content on a share, is controlled using file system access control lists (ACL). For details, see Setting POSIX ACLs on a Samba Share

Configuring User and Group-based Share Access

Share-based access control enables you to grant or deny access to a share for certain users and groups. For example, to enable all members of the Domain Users group to access a share while access is denied for the example_user account, add the following parameters to the share's configuration:

       valid users = +SAMDOM\"Domain Users"
       invalid users = +SAMDOM\example_user

The invalid users parameter has a higher priority than the valid users parameter. For example, if the example_user account is a member of the Domain Users group, access is denied for this account in the previous example.

For further details, see the parameter descriptions in the smb.conf(5) man page.

Configuring Host-based Share Access

Host-based access control enables you to grant or deny access to a share based on host names, IP addresses, or IP ranges. For example, to enable the 127.0.0.1 IP address, the 10.99.0.0/24 IP range, and the GoodHost host name to access a share, and additionally deny access to the code>BadHost host name, add the following parameters to the share's configuration:

       hosts allow = 127.0.0.1 10.99.0.0/24 GoodHost
       hosts deny = BadHost

The hosts deny parameter has a higher priority than the hosts allow parameter. For example, if the BadHost resolves to an IP address that is listed in the hosts allow parameter, access to this host is denied.

For further details, see the parameter descriptions in the smb.conf(5) man page.