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docs/Install-Guide/install-guide-2.2.2/node136.html
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docs/Install-Guide/install-guide-2.2.2/node136.html
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<!DOCTYPE HTML PUBLIC "-//W3O//DTD W3 HTML 2.0//EN">
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<!Converted with LaTeX2HTML 95.1 (Fri Jan 20 1995) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds >
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<HEAD>
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<TITLE>3.11.4 Stopping and restarting jobs</TITLE>
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</HEAD>
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<BODY>
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<meta name="description" value="3.11.4 Stopping and restarting jobs">
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<meta name="keywords" value="gs">
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<meta name="resource-type" value="document">
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<meta name="distribution" value="global">
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<P>
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<BR> <HR><A NAME=tex2html3472 HREF="node137.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A> <A NAME=tex2html3470 HREF="node132.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A> <A NAME=tex2html3466 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <A NAME=tex2html3474 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <A NAME=tex2html3475 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="index" SRC="index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3473 HREF="node137.html">3.12 Using the vi </A>
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<B>Up:</B> <A NAME=tex2html3471 HREF="node132.html">3.11 Job Control</A>
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<B> Previous:</B> <A NAME=tex2html3467 HREF="node135.html">3.11.3 Backgrounding and killing </A>
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<BR> <HR> <P>
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<H2><A NAME=SECTION005114000000000000000>3.11.4 Stopping and restarting jobs</A></H2>
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<P>
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<A NAME=3498> </A>
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There is another way to put a job into the background. You can
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start the job normally (in the foreground), <b>stop</b> the job,
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and then restart it in the background.
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<P>
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First, start the <tt>yes</tt> process in the foreground, as you
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normally would:
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<P><TT> /home/larry# <em>yes <b>></b> /dev/null</em>
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<P></TT>
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Again, because <tt>yes</tt> is running in the foreground, you shouldn't get
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your shell prompt back.
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<P>
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Now, instead of interrupting the job with <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img194.gif">, we'll <em>suspend</em>
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the job. Suspending a job doesn't kill it: it only temporarily stops the
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job until you restart it. To do this, you hit the suspend key, which
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is usually <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img195.gif">.
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<P><TT> /home/larry# <em>yes <b>></b> /dev/null</em> <BR>
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<IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img196.gif"> <BR>
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<code>[1]+ Stopped yes >/dev/null</code> <BR>
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/home/larry#
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<P></TT>
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While the job is suspended, it's simply not running. No CPU time is
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used for the job. However, you can
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restart the job, which will cause the job to run again as if nothing ever
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happened. It will continue to run where it left off.
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<P>
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<A NAME=3571> </A>
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<A NAME=3513> </A>
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To restart the job in the foreground, use the command
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<tt>fg</tt> (for ``foreground'').
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<P><TT> /home/larry# <em>fg</em> <BR>
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yes >/dev/null
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<P></TT>
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<A NAME=3518> </A>
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<A NAME=3572> </A>
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The shell prints the name of the command again so you're aware of which job
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you just put into the foreground. Stop the job again, with <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img197.gif">.
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This time, use the command <tt>bg</tt> to put the job into the background.
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This will cause the command to run just as if you started the command
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with ``<tt>&</tt>'' as in the last section.
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<P><TT> /home/larry# <tt>bg</tt> <BR>
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<code>[1]+</code> yes >/dev/null & <BR>
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/home/larry#
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<P></TT>
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And we have our prompt back. <tt>jobs</tt> should report that <tt>yes</tt>
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is indeed running, and we can kill the job with <tt>kill</tt> as we
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did before.
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<P>
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How can we stop the job again? Using <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img198.gif"> won't work, because
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the job is in the background. The answer is to put the job in the
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foreground, with <tt>fg</tt>, and then stop it. As it turns out you can use
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<tt>fg</tt> on either stopped jobs or jobs in the background.
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<P>
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There is a big difference between a job in the background and a job
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which is stopped. A stopped job is not running---it's not using any
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CPU time, and it's not doing any work (the job still occupies
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system memory, although it may be swapped out to disk). A job in the
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background is running, and using memory, as well as completing some task
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while you
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do other work. However, a job in the background may try to display text on
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to your terminal, which can be annoying if you're trying to work on
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something else. For example, if you used the command
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<P><TT> /home/larry# <em>yes &</em>
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<P></TT>
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without redirecting stdout to <tt>/dev/null</tt>, a stream of <tt>y</tt>'s
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would be printed to your screen, without any way of interrupting it (you
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can't use <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img199.gif"> to interrupt jobs in the background).
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In order to stop the endless <tt>y</tt>'s, you'd have to use the <tt>fg</tt>
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command, to bring the job to the foreground, and then use <IMG BORDER=0 ALIGN=BOTTOM ALT="" SRC="img200.gif">
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to kill it.
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<P>
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Another note. The <tt>fg</tt> and <tt>bg</tt> commands normally foreground
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or background the job which was last stopped (indicated by a
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``<tt>+</tt>'' next to the job number when you use the command <tt>jobs</tt>).
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If you are running multiple jobs at once, you can foreground or
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background a specific job by giving the job ID as
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an argument to <tt>fg</tt> or <tt>bg</tt>, as in
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<P><TT> /home/larry# <em>fg %2</em>
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<P></TT>
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(to foreground job number 2), or
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<P><TT> /home/larry# <em>bg %3</em>
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<P></TT>
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(to background job number 3). You can't use process ID numbers with
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<tt>fg</tt> or <tt>bg</tt>.
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<P>
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Furthermore, using the job number alone, as in
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<P><TT> /home/larry# <em>%2</em>
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<P></TT>
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is equivalent to
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<P><TT> /home/larry# <em>fg %2</em>
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<P></TT>
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<P>
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Just remember that using job control is a feature of the shell. The
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commands <tt>fg</tt>, <tt>bg</tt> and <tt>jobs</tt> are internal to the shell.
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If for some reason you use a shell which does not support job control,
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don't expect to find these commands available.
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<P>
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In addition, there are some aspects of job control which differ between
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Bash and Tcsh. In fact, some shells don't provide job control at
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all---however, most shells available for Linux support job control.
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<P>
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<A NAME=3564> </A>
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<P>
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<P>
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<BR> <HR><A NAME=tex2html3472 HREF="node137.html"><IMG ALIGN=BOTTOM ALT="next" SRC="next_motif.gif"></A> <A NAME=tex2html3470 HREF="node132.html"><IMG ALIGN=BOTTOM ALT="up" SRC="up_motif.gif"></A> <A NAME=tex2html3466 HREF="node135.html"><IMG ALIGN=BOTTOM ALT="previous" SRC="previous_motif.gif"></A> <A NAME=tex2html3474 HREF="node1.html"><IMG ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <A NAME=tex2html3475 HREF="node250.html"><IMG ALIGN=BOTTOM ALT="index" SRC="index_motif.gif"></A> <BR>
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<B> Next:</B> <A NAME=tex2html3473 HREF="node137.html">3.12 Using the vi </A>
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<B>Up:</B> <A NAME=tex2html3471 HREF="node132.html">3.11 Job Control</A>
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<B> Previous:</B> <A NAME=tex2html3467 HREF="node135.html">3.11.3 Backgrounding and killing </A>
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<BR> <HR> <P>
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<BR> <HR>
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<P><ADDRESS>
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<I>Matt Welsh <BR>
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mdw@sunsite.unc.edu</I>
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</ADDRESS>
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</BODY>
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