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<!DOCTYPE html>
<html>
<head>
<title>ProFTPD: Controls</title>
</head>

<hr>
<center><h2>ProFTPD: Controls and <code>mod_ctrls</code></h2></center>
<hr>

What Controls Are 
ProFTPD version 1.2.10rc1 introduced a new capability: Controls. Controls
are a way to communicate directly with a standalone <code>proftpd</code> daemon
while it is running. This provides administrators a way to alter the
daemon's behavior in real time, without having to restart the daemon and
have it re-read its configuration. Changing log levels, kicking connected
clients, disabling individual virtual servers, etc. are all possible.
The Controls functionality includes an API that third-party modules can
use to add new control actions.

The functionality involves a client and a server communicating over a Unix
domain socket, using a simple text-based protocol. A new program,
<code>ftpdctl</code>, is distributed with ProFTPD; <code>ftpdctl</code> is a
Controls client. The server side of the Controls functionality is the
<a href="../modules/mod_ctrls.html"><code>mod_ctrls</code></a> module, which is
compiled into a <code>proftpd</code> daemon when the --enable-ctrls
configure option is used. Note, however, that the Controls functionality only
works for <code>proftpd</code> daemons whose <code>ServerType</code> is
<code>standalone</code>; <code>proftpd</code> daemons run via inetd/xinetd
cannot support Controls and the <code>ftpdctl</code> program.

Configuring <code>mod_ctrls</code> 
Here's an example configuration for <code>mod_ctrls</code>:
<pre>
 &lt;IfModule mod_ctrls.c&gt;
 ControlsEngine on
 ControlsACLs all allow group ftpadm
 ControlsMaxClients 2
 ControlsLog /var/log/proftpd/controls.log
 ControlsInterval 5
 ControlsSocket /tmp/ctrls.sock
 ControlsSocketOwner ftpd ftpd
 ControlsSocketACL allow group ftpadm
 &lt;/IfModule&gt;
</pre>
The first configuration directive you will want to use is the
<code>ControlsEngine</code> directive, which enables the processing of
Controls requests by the engine within the <code>mod_ctrls</code>
engine.

When first configuring <code>mod_ctrls</code> and its modules, you will
probably want to configure a <code>ControlsLog</code>. The
<code>mod_ctrls</code> modules will log any errors they have to this
file (unless the module has its own module-specific log), as well as all
control requests made using <code>ftpdctl</code>. Like most
<code>proftpd</code> log files, the directive should use the full
path to the log file, and the file cannot be in a world-writeable directory.

The <code>ControlsInterval</code> directive configures how often
<code>mod_ctrls</code> checks for connecting clients such as
<code>ftpdctl</code>. Often when using <code>ftpdctl</code>, the system
administrator may notice a long pause before <code>ftpdct</code> responds.
This delay is probably caused by the configured <code>ControlsInterval</code>.
A related directive is <code>ControlsMaxClients</code>, which sets how
many clients are handled at one time. If more than the configured maximum
number of clients are attempting to send control requests,
<code>mod_ctrls</code> will wait to handle the remaining clients until its
next check.

The <code>ControlsSocket</code> directive is used to configure the path
to the Unix domain socket on which <code>mod_ctrls</code> should listen.
This path should be in a place where <code>ftpdctl</code> users have
access to it, and should have read and write permissions. The
<code>ControlsSocketOwner</code> directive explicitly configures the
ownership the created Unix domain socket file should have. This means
that the configuration above:
<pre>
 ControlsSocket /tmp/ctrls.sock
 ControlsSocketOwner ftpd ftpd
</pre>
overrides the default location of the Unix domain socket, and tells
<code>mod_ctrls</code> to use <code>/tmp/ctrls.sock</code>, and to make
the socket owned by user <code>ftpd</code> and group <code>ftpd</code>.
The default ownership of the socket is user <code>root</code>, group
<code>root</code>.

<a name="ACLs"></a>
Controls Access Control Lists 
Communicating with the daemon process allows for some great features, but
it also allows the potential to easily abuse the system. Thus, by default,
all users including user <code>root</code> are denied access to all
<code>ftpdctl</code> actions. Access for control actions must be
explicitly granted. Also, be aware that the users and groups configured
in these ACLs are system users and groups, not the virtual users
and groups that <code>proftpd</code> may have been configured to use.
The group will be only the primary group of the user; supplemental group
memberships are currently ignored.

The <code>mod_ctrls</code> first checks whether the connecting client has
been granted the ability to use the Unix domain socket itself. This access
list is controlled by the <code>ControlsSocketACL</code> directive. By
default, every Controls client can use the socket. Thus, in the example
configuration above:
<pre>
 ControlsSocketACL allow group ftpadm
</pre>
only the system group <code>ftpadm</code> would be allowed to send Controls
requests to the Unix domain socket; all other users and groups will be
denied.

Next, ACLs on the specific control action requested by the connecting
client will be check. Most modules that use the Controls API will have their
own module-specific directives for setting ACLs on the specific actions
implemented by that module. For <code>mod_ctrls</code>, the
<code>ControlsACLs</code> configuration directive is used. In the
example configuration we see:
<pre>
 ControlsACLs all allow group ftpadm
</pre>
which allows only the system group <code>ftpadm</code> to use all of the
control actions provided by <code>mod_ctrls</code>. If one wanted to
allow all users to use all of the control actions, it would be:
<pre>
 ControlsACLs all allow user *
</pre>
However, if one wanted to specify separate ACLs for separate actions, then
the <code>ControlsACLs</code> directive would be used multiple times, like
so:
<pre>
 ControlsACLs insctrl allow group wheel
 ControlsACLs lsctrl allow user *
 ControlsACLs rmctrl deny group ftp
</pre>

Why is there such complexity for a simple client/server interaction? The
primary answer is that the running <code>proftpd</code> daemon has a lot of
privileges, and access to the running daemon should be strictly controlled.
Allow few people to have access via control actions; those few should be able
to use only the control actions necessary.

What Controls Do 
The <code>mod_ctrls</code> module provides basic control actions,
or commands that <code>ftpdctl</code> can send to the daemon:
<ul>
 <li><code>help</code> 
 Lists all registered control actions and a brief description for each
 </li>

<li><code>insctrl</code> 
 Reenable a disabled control action
 </li>

<li><code>lsctrl</code> 
 Lists all enabled control actions and the modules providing them
 </li>

<li><code>rmctrl</code> 
 Disable a control action
 </li>
</ul>

Denied Actions Versus Disabled Actions 
What is the difference between an action that has been denied via an ACL
versus an action that has been disabled using the <code>rmctrl</code> action?
A disabled action cannot be used by any client, regardless of any ACLs that
have been configured for that action. Thus if a system administrator
deemed that a particular control action should not be used by anyone, that
action can be disabled. The <code>rmctrl</code> action can disable any
action implemented by any module using the Controls API, not just actions
provided by <code>mod_ctrls</code>. Once disabled, a given action can be
re-enabled using the <code>insctrl</code> action. The <code>insctrl</code>
and <code>rmctrl</code> actions, in addition to <code>lsctrl</code>, cannot
themselves be disabled. For example, to disable an action called
<code>foo</code>:
<pre>
 # ftpdctl rmctrl foo
 ftpdctl: 'foo' control disabled
 # ftpdctl lsctrl
 ftpdctl: help (mod_ctrls.c)
 ftpdctl: insctrl (mod_ctrls.c)
 ftpdctl: lsctrl (mod_ctrls.c)
 ftpdctl: rmctrl (mod_ctrls.c)
</pre>
Note that the <code>foo</code> action is not listed by <code>lsctrl</code>.
Now, re-enable that action:
<pre>
 # ftpdctl insctrl foo
 ftpdctl: 'foo' control enabled
 # ftpdctl lsctrl
 ftpdctl: foo (mod_foo.c)
 ftpdctl: help (mod_ctrls.c)
 ftpdctl: insctrl (mod_ctrls.c)
 ftpdctl: lsctrl (mod_ctrls.c)
 ftpdctl: permit (mod_ban.c)
 ftpdctl: rmctrl (mod_ctrls.c)
</pre>
And now the <code>foo</code> action, provided by the module
<code>mod_foo.c</code>, appears in the <code>lsctrl</code> listing.

The following shows an example of attempting to disable the <code>lsctrl</code>
action. It demonstrates the use of the <code>-v</code> command-line
option for <code>ftpdctl</code>, for showing a verbose interaction with
<code>mod_ctrls</code>:
<pre>
 # ftpdctl -v lsctrl
 ftpdctl: adding &quot;lsctrl&quot; to reqargv
 ftpdctl: contacting server
 ftpdctl: sending control request
 ftpdctl: receiving control response
 ftpdctl: debug (mod_ctrls_admin.c)
 ...

# ftpdctl rmctrl lsctrl

# ftpdctl -v lsctrl
 ftpdctl: adding "lsctrl" to reqargv
 ftpdctl: contacting server
 ftpdctl: sending control request
 ftpdctl: receiving control response
 ftpdctl: access denied
</pre>
The &quot;access denied&quot; message happens because of the special status
of the <code>lsctrl</code> action which keeps it from being disablable.

Admin Controls 
The <code>mod_ctrls</code> module, by itself, is rather unexciting. Other
modules, such as <code>mod_ctrls_admin</code>, provide more interesting
and useful control actions, including:
<ul>
 <li><code>debug</code>
 <li><code>dump</code>
 <li><code>kick</code>
 <li><code>restart</code>
 <li><code>shutdown</code>
 <li><code>start</code>
 <li><code>status</code>
 <li><code>stop</code>
 <li><code>trace</code>
</ul>
These actions provide basic administrative control over the running
<code>proftpd</code> daemon; see the <code>mod_ctrls_admin</code>
<a href="../contrib/mod_ctrls_admin.html">documentation</a> for more details.

A basic <code>mod_ctrls_admin</code> configuration is:
<pre>
 &lt;IfModule mod_ctrls_admin.c&gt;
 AdminControlsACLs all allow user *
 &lt;/IfModule&gt;
</pre>
will allows anyone to use any <code>mod_ctrls_admin</code> control action.

Here is another configuration, encompassing both <code>mod_ctrls</code>
and <code>mod_ctrls_admin</code>:
<pre>
 &lt;IfModule mod_ctrls.c&gt;
 ControlsEngine on
 ControlsACLs all allow group ftpadm
 ControlsMaxClients 2
 ControlsLog /var/log/proftpd/controls.log
 ControlsInterval 5
 ControlsSocketACL allow group ftpadm
 ControlsSocket /tmp/ctrls.sock
 ControlsSocketOwner ftpd ftpd

&lt;IfModule mod_ctrls_admin.c&gt;
 AdminControlsACLs all allow user dave,bob,lisa
 &lt;/IfModule&gt;
 &lt;/IfModule&gt;
</pre>
In this configuration, users <code>dave</code>, <code>bob</code>, and
<code>lisa</code> are allowed to use all of the control actions supplied
by <code>mod_ctrls_admin</code>. However, unless these users are members
of group <code>ftpadm</code>, access will be denied. Only group
<code>ftpadm</code> has been allowed access to the <code>mod_ctrls</code>
socket itself by the <code>ControlsSocketACL</code> directive.

What about configuring an ACL for a given control that includes both
users and groups? Use:
<pre>
 AdminControlsACLs restart allow user dave,lisa
 AdminControlsACLs restart allow group ftpadm
</pre>
What if user <code>dave</code> is not a member of group <code>ftpadm</code>?
If configured, both user and group ACLs must deny the client.
If either allows access, the client can use that control action.

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