Editing UBC auxiliary parameters

{{UBC toc}}

Configuration of primary and secondary resource control parameters is
important for security and stability of the whole system. Auxiliary
parameters differ much from primary and secondary parameters in this respect.

The primary functions of auxiliary parameters are the following.
<ul>
<li>These parameters improve application's handling of errors and resource
consumption limitations.

Without these auxiliary parameters, possible bugs in applications (such
as forgetting to unlock locked files or forgetting to collect signals) will
cause slowdown and, after some time, killing of the applications because
of memory exhaustion. In presence of these parameters, applications
will notice the problem (because, for example, attempts to create new
file locks start to fail) and show an appropriate message helping to
debug the problem.

Another example. Each object such as opened file or established network
connection consume certain resources. When the Virtual Environment
is close to exhaustion of the resources allowed to him, it is
usually better to refuse creation of new object than to allow it but deny
memory allocation or terminate (in case of complete exhaustion of the
resources) an already running application.
</li>

<li>
These parameters improve fault isolation between applications in the
same Virtual Environment. Failures or misbehavior of one application
inside a Virtual Environment is more likely to cause hitting a
limit on some auxiliary parameter and normal termination of this mis-
behaving application, rather than abnormal termination of some other
long-running application inside the same Virtual Environment.
</li>

<li>
These parameters may be used to impose some administrative limits
on the Virtual Environment (for example, to not allow the user to run
database servers by limiting the amount of [[shmpages]], or limiting the
number of simultaneous shell sessions through [[numpty]]).
</li>
</ul>

So, auxiliary parameters play a role similar to limits imposed by
<code>setrlimit(2)</code> interface and limits configurable by
<code>sysctl(8)</code> in standard
Linux installations.

Because of this helper role in resource control, system management software
may show auxiliary parameters only in advanced mode for experienced
administrators and hide them in “basic” management modes.

== lockedpages ==
Process pages not allowed to be swapped out (pages locked by <code>mlock(2)</code>).

The size of these pages is also accounted into <code>[[kmemsize]]</code>.
The <code>barrier</code> may be set equal to the <code>limit</code> or may allow
some gap between the <code>barrier</code> and the <code>limit</code>, depending
on the nature of applications using memory locking features.

Note that typical server applications like Web, FTP, mail servers
do not use memory locking features.

The configuration of this parameter doesn't affect security and
stability of the whole system or isolation between Virtual Environments.
Its configuration affects functionality and resource shortage reaction
of applications in the given Virtual Environment only.

== shmpages ==
The total size of shared memory (IPC, shared anonymous mappings and
<code>tmpfs</code> objects).

These pages are also accounted into <code>[[privvmpages]]</code>.

The <code>barrier</code> should be set equal to the <code>limit</code>.
The configuration of this parameter doesn't affect security and
stability of the whole system or isolation between Virtual Environments.
Its configuration affects functionality and resource shortage reaction
of applications in the given Virtual Environment only.