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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2//EN">
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<TITLE>The Answer Guy 36:
Letting Those Transfers Run Unattended
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<H4>"The Linux Gazette...<I>making Linux just a little more fun!</I>"</H4>
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<H1><A NAME="answer">
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<font color="#B03060">The Answer Guy</font>
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<H4>By James T. Dennis,
<a href="mailto:answerguy@ssc.com">answerguy@ssc.com</a><BR>
Starshine Technical Services,
<A HREF="http://www.starshine.org/">http://www.starshine.org/</A>
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<!-- begin 10 -->
<H3 align="left"><img src="../../gx/dennis/qbubble.gif" height="50" width="60"
alt="(?) " border="0">
Letting Those Transfers Run Unattended
</H3>
<p><strong>From Terry Singleton on Wed, 02 Dec 1998
</strong></p>
<!-- ::
Letting Those Transfers Run Unattended
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:: -->
<BLOCKQUOTE>
</BLOCKQUOTE>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
While at home, dialed into work with my 56Kb modem, I sometimes
run across very large interesting looking applications. I often
wish that there were a way for me to telnet to my Linux box at
work and start the download. When I got to work the next day the
download would have hopefully completed.
</STRONG></P>
<P><STRONG>
Question: Is there a way for me to start my download remotely,
disconnect from the Linux server and have the server continue to
download the file(s)??
</STRONG></P>
<P><STRONG>
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" alt="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Yes. The most obvious is to use '<tt>screen</tt>' - this will
let you start interactive processes over a dialup or
telnet connect (or within an xterm, on a VC), then
you can "multiplex" multiple interactive programs
and you can "detach" the whole session from your
terminal/connection.
</BLOCKQUOTE>
<BLOCKQUOTE>
Later, when you reconnect you can re-attach to your
'screen' session using the command:
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
screen -r
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
... assuming that you only have one of them
going. If you've started multiple 'screen' sessions you
can select the one to which you want to re-attach using
additional command switches (read the man page for that).
</BLOCKQUOTE>
<BLOCKQUOTE>
I routinely use 'screen' (I'm using from a virtual console
right now). If I leave this session like this and connect
from my terminal in the living from (to watch a little
CNN or "Law & Order" as I work) I just use the command:
</BLOCKQUOTE>
<BLOCKQUOTE><BLOCKQUOTE><CODE>
screen -r -d
</CODE></BLOCKQUOTE></BLOCKQUOTE>
<BLOCKQUOTE>
... to simultaneously detach and reattach my screen session
--- to effectively "yank it over to my terminal."
</BLOCKQUOTE>
<BLOCKQUOTE>
Another advantage of using 'screen' is that my session
is preserved if I get disconnected. (There's an
"auto-detach" feature). So, you can leave the same
session saving state in up to ten programs for weeks, even
months at a time. (I have three copies of xemacs, a
copy of lynx and a couple of shell prompts to the local
and some of the other hosts on my net open as I type this).
</BLOCKQUOTE>
<BLOCKQUOTE>
I do try to force myself to drop out of my screen session at
least once a month.
</BLOCKQUOTE>
<BLOCKQUOTE>
If you're using FTP to get these files you can also
use the '<tt>ncftp</tt>' command line features, including a "re-dial"
which will keep trying to get to that busy FTP site
until it gets your files. There's also a program called
'<tt>lftp</tt>' that is a "command line driven, script friendly"
FTP client.
</BLOCKQUOTE>
<BLOCKQUOTE>
Another approach would be to use '<tt>expect</tt>' and/or Kermit
scripts which you start at the remote and run
"asynchronously" (in the background by slapping an
'<tt>&</tt>' ampersand on the end of the command or by
hitting [Ctrl]+[Z] to "suspend" the job and issuing
the 'bg' command to restart it as though you'd put
the '<tt>&</tt>' on it to begin with.
</BLOCKQUOTE>
<BLOCKQUOTE>
Note that this "job control" feature (the [Ctrl]+[Z]
and '<tt>bg</tt>' stuff) only works with non-interactive programs.
Interactive programs are likely to stop with a "waiting
on terminal input" message. '<tt>screen</tt>' and any properly
written '<tt>expect</tt>' script will cope with those because they
set up a Unix domain socket as a sort of "virtual" terminal
to control the interactive software.
</BLOCKQUOTE>
<BLOCKQUOTE>
</BLOCKQUOTE>
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Regards,
<br>Terry Singleton
<br>Canadore College, Network Analyst
</STRONG></P>
<!-- sig -->
<!-- end 10 -->
<hr width="40%" align="center">
<!-- begin 92 -->
<H3 align="left"><img src="../../gx/dennis/qbubble.gif" height="50" width="60"
alt="(?) " border="0">
Letting Those Transfers Run Unattended
</H3>
<p><strong>From Terry Singleton on Fri, 25 Dec 1998
</strong></p>
<!-- ::
More on:
Letting Those Transfers Run Unattended
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
:: -->
<P><STRONG><IMG SRC="../../gx/dennis/qbub.gif" ALT="(?)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
Where do I find <EM>screen</EM> I searched my system and www.freshmeat.net but
could not find the app you mentioned. I am running RedHat 5.1 and I believe
installed almost everything.
</STRONG></P>
<P><STRONG>
thanks.
</STRONG></P>
<BLOCKQUOTE><IMG SRC="../../gx/dennis/bbub.gif" alt="(!)"
HEIGHT="28" WIDTH="50" BORDER="0"
>
That's odd. When I use freshmeat's "Quickfinder" it's
the first entry that shows up. (Maybe the older version
wasn't listed. A new version was just released recently
--- after you sent me this message I think).
</BLOCKQUOTE>
<BLOCKQUOTE>
Here's the Freshmeat "AppIndex" URL:
</BLOCKQUOTE>
<BLOCKQUOTE><dl>
<dt>( freshmeat ) - ( details of "screen" )
<dd><tt><A HREF="http://appindex.freshmeat.net/view/913939067"
>http://appindex.freshmeat.net/view/913939067</A></tt>
</dl></BLOCKQUOTE>
<BLOCKQUOTE>
... and here's the main web page:
</BLOCKQUOTE>
<BLOCKQUOTE><dl>
<dt>screen - GNU Project - Free Software Foundation (FSF)
<dd><tt><A HREF="http://www.gnu.org/software/screen"
>http://www.gnu.org/software/screen</A></tt>
</dl></BLOCKQUOTE>
<BLOCKQUOTE>
It's also easy to find at the Filewatcher site
(<A HREF="http://filewatcher.org">http://filewatcher.org</A>
<EM>formerly</EM> lfw.linuxhq.com) and
at the Linux Archive Search (<A HREF="http://las.ml.org"
>http://las.ml.org</A>).
</BLOCKQUOTE>
<BLOCKQUOTE>
However, Freshmeat returned the most recent version and
the canonical web site, while the others showed dozens
of links to older versions and other packages (with the
string 'screen' in their names) and no information about
the package. So Freshmeat's my first choice at this point.
</BLOCKQUOTE>
<!-- sig -->
<!-- end 92 -->
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<P> <hr> <P>
<H5 align="center"><a href="http://www.linuxgazette.com/ssc.copying.html"
>Copyright ©</a> 1999, James T. Dennis
<BR>Published in <I>The Linux Gazette</I> Issue 36 January 1999</H5>
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