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 Previous:&nbsp;<a rel="previous" accesskey="p" href="Traditional-Scheduling-Intro.html#Traditional-Scheduling-Intro">Traditional Scheduling Intro</a>,
 Up:&nbsp;<a rel="up" accesskey="u" href="Traditional-Scheduling.html#Traditional-Scheduling">Traditional Scheduling</a>
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 <h5 class="subsubsection">22.3.4.2 Functions For Traditional Scheduling</h5>

 <p><a name="index-sys_002fresource_002eh-2755"></a>This section describes how you can read and set the nice value of a
 process.  All these symbols are declared in <samp><span class="file">sys/resource.h</span></samp>.

    <p>The function and macro names are defined by POSIX, and refer to
 "priority," but the functions actually have to do with nice values, as
 the terms are used both in the manual and POSIX.

    <p>The range of valid nice values depends on the kernel, but typically it
 runs from <code>-20</code> to <code>20</code>.  A lower nice value corresponds to
 higher priority for the process.  These constants describe the range of
 priority values:

      <dl>
 <!-- sys/resource.h -->
 <!-- BSD -->
 <dt><code>PRIO_MIN</code><a name="index-PRIO_005fMIN-2756"></a><dd>The lowest valid nice value.

      <!-- sys/resource.h -->
      <!-- BSD -->
      <br><dt><code>PRIO_MAX</code><a name="index-PRIO_005fMAX-2757"></a><dd>The highest valid nice value.
 </dl>

 <!-- sys/resource.h -->
 <!-- BSD,POSIX -->
 <div class="defun">
 &mdash; Function: int <b>getpriority</b> (<var>int class, int id</var>)<var><a name="index-getpriority-2758"></a></var><br>
 <blockquote><p>Return the nice value of a set of processes; <var>class</var> and <var>id</var>
 specify which ones (see below).  If the processes specified do not all
 have the same nice value, this returns the lowest value that any of them
 has.

         <p>On success, the return value is <code>0</code>.  Otherwise, it is <code>-1</code>
 and <code>ERRNO</code> is set accordingly.  The <code>errno</code> values specific
 to this function are:

           <dl>
 <dt><code>ESRCH</code><dd>The combination of <var>class</var> and <var>id</var> does not match any existing
 process.

           <br><dt><code>EINVAL</code><dd>The value of <var>class</var> is not valid.
 </dl>

         <p>If the return value is <code>-1</code>, it could indicate failure, or it could
 be the nice value.  The only way to make certain is to set <code>errno =
 0</code> before calling <code>getpriority</code>, then use <code>errno != 0</code>
 afterward as the criterion for failure.
 </p></blockquote></div>

 <!-- sys/resource.h -->
 <!-- BSD,POSIX -->
 <div class="defun">
 &mdash; Function: int <b>setpriority</b> (<var>int class, int id, int niceval</var>)<var><a name="index-setpriority-2759"></a></var><br>
 <blockquote><p>Set the nice value of a set of processes to <var>niceval</var>; <var>class</var>
 and <var>id</var> specify which ones (see below).

         <p>The return value is <code>0</code> on success, and <code>-1</code> on
 failure.  The following <code>errno</code> error condition are possible for
 this function:

           <dl>
 <dt><code>ESRCH</code><dd>The combination of <var>class</var> and <var>id</var> does not match any existing
 process.

           <br><dt><code>EINVAL</code><dd>The value of <var>class</var> is not valid.

           <br><dt><code>EPERM</code><dd>The call would set the nice value of a process which is owned by a different
 user than the calling process (i.e., the target process' real or effective
 uid does not match the calling process' effective uid) and the calling
 process does not have <code>CAP_SYS_NICE</code> permission.

           <br><dt><code>EACCES</code><dd>The call would lower the process' nice value and the process does not have
 <code>CAP_SYS_NICE</code> permission.
 </dl>

         </blockquote></div>

    <p>The arguments <var>class</var> and <var>id</var> together specify a set of
 processes in which you are interested.  These are the possible values of
 <var>class</var>:

      <dl>
 <!-- sys/resource.h -->
 <!-- BSD -->
 <dt><code>PRIO_PROCESS</code><a name="index-PRIO_005fPROCESS-2760"></a><dd>One particular process.  The argument <var>id</var> is a process ID (pid).

      <!-- sys/resource.h -->
      <!-- BSD -->
      <br><dt><code>PRIO_PGRP</code><a name="index-PRIO_005fPGRP-2761"></a><dd>All the processes in a particular process group.  The argument <var>id</var> is
 a process group ID (pgid).

      <!-- sys/resource.h -->
      <!-- BSD -->
      <br><dt><code>PRIO_USER</code><a name="index-PRIO_005fUSER-2762"></a><dd>All the processes owned by a particular user (i.e., whose real uid
 indicates the user).  The argument <var>id</var> is a user ID (uid).
 </dl>

    <p>If the argument <var>id</var> is 0, it stands for the calling process, its
 process group, or its owner (real uid), according to <var>class</var>.

 <!-- unistd.h -->
 <!-- BSD -->
 <div class="defun">
 &mdash; Function: int <b>nice</b> (<var>int increment</var>)<var><a name="index-nice-2763"></a></var><br>
 <blockquote><p>Increment the nice value of the calling process by <var>increment</var>.
 The return value is the new nice value on success, and <code>-1</code> on
 failure.  In the case of failure, <code>errno</code> will be set to the
 same values as for <code>setpriority</code>.

         <p>Here is an equivalent definition of <code>nice</code>:

      <pre class="smallexample">          int
           nice (int increment)
           {
             int result, old = getpriority (PRIO_PROCESS, 0);
             result = setpriority (PRIO_PROCESS, 0, old + increment);
             if (result != -1)
                 return old + increment;
             else
                 return -1;
           }
 </pre>
         </blockquote></div>

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	Previous: <a rel="previous" accesskey="p" href="Traditional-Scheduling-Intro.html#Traditional-Scheduling-Intro">Traditional Scheduling Intro</a>,
	Up: <a rel="up" accesskey="u" href="Traditional-Scheduling.html#Traditional-Scheduling">Traditional Scheduling</a>
	<hr>
	</div>

	<h5 class="subsubsection">22.3.4.2 Functions For Traditional Scheduling</h5>

	<p><a name="index-sys_002fresource_002eh-2755"></a>This section describes how you can read and set the nice value of a
	process. All these symbols are declared in <samp><span class="file">sys/resource.h</span></samp>.

	<p>The function and macro names are defined by POSIX, and refer to
	"priority," but the functions actually have to do with nice values, as
	the terms are used both in the manual and POSIX.

	<p>The range of valid nice values depends on the kernel, but typically it
	runs from <code>-20</code> to <code>20</code>. A lower nice value corresponds to
	higher priority for the process. These constants describe the range of
	priority values:

	<dl>
	<!-- sys/resource.h -->
	<!-- BSD -->
	<dt><code>PRIO_MIN</code><a name="index-PRIO_005fMIN-2756"></a><dd>The lowest valid nice value.

	<!-- sys/resource.h -->
	<!-- BSD -->
	<br><dt><code>PRIO_MAX</code><a name="index-PRIO_005fMAX-2757"></a><dd>The highest valid nice value.
	</dl>

	<!-- sys/resource.h -->
	<!-- BSD,POSIX -->
	<div class="defun">
	— Function: int <b>getpriority</b> (<var>int class, int id</var>)<var><a name="index-getpriority-2758"></a></var><br>
	<blockquote><p>Return the nice value of a set of processes; <var>class</var> and <var>id</var>
	specify which ones (see below). If the processes specified do not all
	have the same nice value, this returns the lowest value that any of them
	has.

	<p>On success, the return value is <code>0</code>. Otherwise, it is <code>-1</code>
	and <code>ERRNO</code> is set accordingly. The <code>errno</code> values specific
	to this function are:

	<dl>
	<dt><code>ESRCH</code><dd>The combination of <var>class</var> and <var>id</var> does not match any existing
	process.

	<br><dt><code>EINVAL</code><dd>The value of <var>class</var> is not valid.
	</dl>

	<p>If the return value is <code>-1</code>, it could indicate failure, or it could
	be the nice value. The only way to make certain is to set <code>errno =
	0</code> before calling <code>getpriority</code>, then use <code>errno != 0</code>
	afterward as the criterion for failure.
	</p></blockquote></div>

	<!-- sys/resource.h -->
	<!-- BSD,POSIX -->
	<div class="defun">
	— Function: int <b>setpriority</b> (<var>int class, int id, int niceval</var>)<var><a name="index-setpriority-2759"></a></var><br>
	<blockquote><p>Set the nice value of a set of processes to <var>niceval</var>; <var>class</var>
	and <var>id</var> specify which ones (see below).

	<p>The return value is <code>0</code> on success, and <code>-1</code> on
	failure. The following <code>errno</code> error condition are possible for
	this function:

	<dl>
	<dt><code>ESRCH</code><dd>The combination of <var>class</var> and <var>id</var> does not match any existing
	process.

	<br><dt><code>EINVAL</code><dd>The value of <var>class</var> is not valid.

	<br><dt><code>EPERM</code><dd>The call would set the nice value of a process which is owned by a different
	user than the calling process (i.e., the target process' real or effective
	uid does not match the calling process' effective uid) and the calling
	process does not have <code>CAP_SYS_NICE</code> permission.

	<br><dt><code>EACCES</code><dd>The call would lower the process' nice value and the process does not have
	<code>CAP_SYS_NICE</code> permission.
	</dl>

	</blockquote></div>

	<p>The arguments <var>class</var> and <var>id</var> together specify a set of
	processes in which you are interested. These are the possible values of
	<var>class</var>:

	<dl>
	<!-- sys/resource.h -->
	<!-- BSD -->
	<dt><code>PRIO_PROCESS</code><a name="index-PRIO_005fPROCESS-2760"></a><dd>One particular process. The argument <var>id</var> is a process ID (pid).

	<!-- sys/resource.h -->
	<!-- BSD -->
	<br><dt><code>PRIO_PGRP</code><a name="index-PRIO_005fPGRP-2761"></a><dd>All the processes in a particular process group. The argument <var>id</var> is
	a process group ID (pgid).

	<!-- sys/resource.h -->
	<!-- BSD -->
	<br><dt><code>PRIO_USER</code><a name="index-PRIO_005fUSER-2762"></a><dd>All the processes owned by a particular user (i.e., whose real uid
	indicates the user). The argument <var>id</var> is a user ID (uid).
	</dl>

	<p>If the argument <var>id</var> is 0, it stands for the calling process, its
	process group, or its owner (real uid), according to <var>class</var>.

	<!-- unistd.h -->
	<!-- BSD -->
	<div class="defun">
	— Function: int <b>nice</b> (<var>int increment</var>)<var><a name="index-nice-2763"></a></var><br>
	<blockquote><p>Increment the nice value of the calling process by <var>increment</var>.
	The return value is the new nice value on success, and <code>-1</code> on
	failure. In the case of failure, <code>errno</code> will be set to the
	same values as for <code>setpriority</code>.

	<p>Here is an equivalent definition of <code>nice</code>:

	<pre class="smallexample"> int
	nice (int increment)
	{
	int result, old = getpriority (PRIO_PROCESS, 0);
	result = setpriority (PRIO_PROCESS, 0, old + increment);
	if (result != -1)
	return old + increment;
	else
	return -1;
	}
	</pre>
	</blockquote></div>

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