ch39_09.htm

the unix power tools

<SPAN
CLASS="link"
>makefiles (<A
CLASS="linkend"
HREF="ch28_13.htm"
TITLE="make Isn't Just for Programmers! "
>28.13</A
>)</SPAN
>,
when you are running the Bourne shell, etc. The principles 
are the same. <EM
CLASS="emphasis"
>nice</EM
> numbers run from -20 to 20, with the default 
being zero. Only the syntax has been changed to confuse you. For the 
standalone version, <CODE
CLASS="literal"
>-</CODE
><EM
CLASS="emphasis"
>n</EM
> requests
a positive <EM
CLASS="emphasis"
>nice</EM
> number (lower priority) and <CODE
CLASS="literal"
>--</CODE
><EM
CLASS="emphasis"
>n</EM
>
requests a negative <EM
CLASS="emphasis"
>nice</EM
> number (higher priority-superuser only). 
Consider these commands:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>$ <CODE
CLASS="userinput"
><B
>nice -6 awk -f proc.awk datafile &gt; awk.out</B
></CODE
>
# <CODE
CLASS="userinput"
><B
>nice --6 awk -f proc.awk datafile &gt; awk.out</B
></CODE
></PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>The first command runs <EM
CLASS="emphasis"
>awk</EM
> with a high <EM
CLASS="emphasis"
>nice</EM
> number (i.e.,
6). The second command, which can be issued only by a superuser, runs
<EM
CLASS="emphasis"
>awk</EM
> with a low <EM
CLASS="emphasis"
>nice</EM
> number (i.e., -6).  If no level is
specified, the default argument is -10.</P
></DIV
><DIV
CLASS="sect2"
><H3
CLASS="sect2"
><A
CLASS="title"
NAME="UPT-ART-68-SECT-1.0.3"
>39.9.3 System V C Shell nice </A
></H3
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="AUTOID-44123"
></A
><A
CLASS="indexterm"
NAME="AUTOID-44126"
></A
>System V takes a slightly different view of <EM
CLASS="emphasis"
>nice</EM
>
numbers. <EM
CLASS="emphasis"
>nice</EM
> levels run from 0 to 39; the default is 20. The
numbers are different but their meanings are the same: 39 corresponds
to the lowest possible priority, and 0 is the highest. A few System V
implementations support real-time submission via <EM
CLASS="emphasis"
>nice</EM
>. Jobs
submitted by root with extremely low <EM
CLASS="emphasis"
>nice</EM
> numbers (-20 or
below) allegedly get all of the CPU's time.  Systems on which
this works properly are very rare and usually advertise support for
real-time processing. In any case, running jobs this way will destroy
multiuser performance. This feature is completely different from
real-time priorities in System V Release 4.</P
><P
CLASS="para"
>With these exceptions, the C shell version of <EM
CLASS="emphasis"
>nice</EM
> is the same as
its BSD cousin. To submit a job at a low priority, use the command:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>% <CODE
CLASS="userinput"
><B
>nice <CODE
CLASS="replaceable"
><I
>command</I
></CODE
></B
></CODE
></PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>This increases the command's niceness by the default amount 
(4, the same as BSD UNIX); <EM
CLASS="emphasis"
>command</EM
> will run at <EM
CLASS="emphasis"
>nice</EM
> 
level 24. To run a job at an arbitrary priority, use one of the
following commands:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>% <CODE
CLASS="userinput"
><B
>nice +</B
></CODE
><CODE
CLASS="replaceable"
><I
>n</I
></CODE
><CODE
CLASS="userinput"
><B
> command</B
></CODE
>
% <CODE
CLASS="userinput"
><B
>nice -</B
></CODE
><CODE
CLASS="replaceable"
><I
>n</I
></CODE
><CODE
CLASS="userinput"
><B
> command</B
></CODE
></PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>where <EM
CLASS="emphasis"
>n</EM
> is an integer between 0 and 19. The <EM
CLASS="emphasis"
>+n</EM
> entry
requests a higher <EM
CLASS="emphasis"
>nice</EM
> level (a decreased priority), while <EM
CLASS="emphasis"
>-n</EM
>
requests a lower <EM
CLASS="emphasis"
>nice</EM
> level (a higher priority). Again, this is
similar to BSD UNIX, with one important difference: <EM
CLASS="emphasis"
>n</EM
> is now
relative to the default <EM
CLASS="emphasis"
>nice</EM
> level. That is, the command: </P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>% <CODE
CLASS="userinput"
><B
>nice +6 awk -f proc.awk datafile &gt; awk.out</B
></CODE
></PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>runs <EM
CLASS="emphasis"
>awk</EM
> at <EM
CLASS="emphasis"
>nice</EM
> level 26.</P
></DIV
><DIV
CLASS="sect2"
><H3
CLASS="sect2"
><A
CLASS="title"
NAME="UPT-ART-68-SECT-1.0.4"
>39.9.4 System V Standalone nice </A
></H3
><P
CLASS="para"
><A
CLASS="indexterm"
NAME="AUTOID-44166"
></A
>Once again, the standalone version of <EM
CLASS="emphasis"
>nice</EM
> is useful if you are
writing makefiles or shell scripts or if you use the Bourne shell as
your interactive shell. It is similar to the C shell version, with
these differences:</P
><UL
CLASS="itemizedlist"
><LI
CLASS="listitem"
><P
CLASS="para"
>With no arguments, standalone <EM
CLASS="emphasis"
>nice</EM
> increases the <EM
CLASS="emphasis"
>nice</EM
> 
number by 10 instead of by 4; this is a significantly greater 
reduction in the program's priority.</P
></LI
><LI
CLASS="listitem"
><P
CLASS="para"
>With the argument <EM
CLASS="emphasis"
>-n</EM
>, <EM
CLASS="emphasis"
>nice</EM
> increases the <EM
CLASS="emphasis"
>nice</EM
> 
number by <EM
CLASS="emphasis"
>n</EM
> (reducing priority).</P
></LI
><LI
CLASS="listitem"
><P
CLASS="para"
>With the argument <EM
CLASS="emphasis"
>-&nbsp;-n</EM
>, <EM
CLASS="emphasis"
>nice</EM
> decreases the <EM
CLASS="emphasis"
>nice</EM
> 
number by <EM
CLASS="emphasis"
>n</EM
> (increasing priority; superuser only).</P
></LI
></UL
><P
CLASS="para"
>Consider these commands:</P
><P
CLASS="para"
><BLOCKQUOTE
CLASS="screen"
><PRE
CLASS="screen"
>$ <CODE
CLASS="userinput"
><B
>nice -6 awk -f proc.awk datafile &gt; awk.out</B
></CODE
>
# <CODE
CLASS="userinput"
><B
>nice --6 awk -f proc.awk datafile &gt; awk.out</B
></CODE
></PRE
></BLOCKQUOTE
></P
><P
CLASS="para"
>The first command runs <EM
CLASS="emphasis"
>awk</EM
> at a higher <EM
CLASS="emphasis"
>nice</EM
> level 
(i.e., 26, which corresponds to a lower priority). The second 
command, which can be given only by the superuser, runs
<EM
CLASS="emphasis"
>awk</EM
> at a lower <EM
CLASS="emphasis"
>nice</EM
> level (i.e., 14).</P
></DIV
><DIV
CLASS="sect1info"
><P
CLASS="SECT1INFO"
>- <SPAN
CLASS="authorinitials"
>ML</SPAN
> <SPAN
CLASS="bibliomisc"
>from O'Reilly &amp; Associates' <CITE
CLASS="citetitle"
>System Performance Tuning</CITE
>, Chapter 3</SPAN
></P
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