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<HTML><!--Distributed by F --><HEAD><TITLE>[Chapter 38] 38.18 nohup </TITLE><METANAME="DC.title"CONTENT="UNIX Power Tools"><METANAME="DC.creator"CONTENT="Jerry Peek, Tim O'Reilly & Mike Loukides"><METANAME="DC.publisher"CONTENT="O'Reilly & Associates, Inc."><METANAME="DC.date"CONTENT="1998-08-04T21:50:05Z"><METANAME="DC.type"CONTENT="Text.Monograph"><METANAME="DC.format"CONTENT="text/html"SCHEME="MIME"><METANAME="DC.source"CONTENT="1-56592-260-3"SCHEME="ISBN"><METANAME="DC.language"CONTENT="en-US"><METANAME="generator"CONTENT="Jade 1.1/O'Reilly DocBook 3.0 to HTML 4.0"><LINKREV="made"HREF="mailto:online-books@oreilly.com"TITLE="Online Books Comments"><LINKREL="up"HREF="ch38_01.htm"TITLE="38. Starting, Stopping, and Killing Processes"><LINKREL="prev"HREF="ch38_17.htm"TITLE="38.17 Automatically Kill Background Processes on Logout in csh"><LINKREL="next"HREF="ch39_01.htm"TITLE="39. Time and Performance"></HEAD><BODYBGCOLOR="#FFFFFF"TEXT="#000000"><DIVCLASS="htmlnav"><H1><IMGSRC="gifs/smbanner.gif"ALT="UNIX Power Tools"USEMAP="#srchmap"BORDER="0"></H1><MAPNAME="srchmap"><AREASHAPE="RECT"COORDS="0,0,466,58"HREF="index.htm"ALT="UNIX Power Tools"><AREASHAPE="RECT"COORDS="467,0,514,18"HREF="jobjects/fsearch.htm"ALT="Search this book"></MAP><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch38_17.htm"TITLE="38.17 Automatically Kill Background Processes on Logout in csh"><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 38.17 Automatically Kill Background Processes on Logout in csh"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><B><FONTFACE="ARIEL,HELVETICA,HELV,SANSERIF"SIZE="-1">Chapter 38<BR>Starting, Stopping, and Killing Processes</FONT></B></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="CHAPTER"HREF="ch39_01.htm"TITLE="39. Time and Performance"><IMGSRC="gifs/txtnexta.gif"SRC="gifs/txtnexta.gif"ALT="Next: 39. Time and Performance"BORDER="0"></A></TD></TR></TABLE> <HRALIGN="LEFT"WIDTH="515"TITLE="footer"></DIV><DIVCLASS="SECT1"><H2CLASS="sect1"><ACLASS="title"NAME="UPT-ART-8005">38.18 nohup </A></H2><PCLASS="para">When UNIX first started, even local terminals very often communicated with the system via short-haul modems. (After all, UNIX was invented bythe phone company.)When someone logged out, the modem hung up thephone - and conversely, if the modem hung up, a "hangup" signal wassent to the login shell, whereupon it terminated, bringing down all its <SPANCLASS="link">child processes (<ACLASS="linkend"HREF="ch38_03.htm"TITLE="Managing Processes: Overall Concepts ">38.3</A>)</SPAN>with it. </P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-43448"></A>In the C shell, processes that you run in the background areimmune to hangups, but in the Bourne shell, a processthat you started in the background might be abruptly terminated.</P><TABLECLASS="para.programreference"BORDER="1"><TR><THVALIGN="TOP"><ACLASS="programreference"HREF="examples/index.htm"TITLE="nohup">nohup</A><BR></TH><TDVALIGN="TOP"><ACLASS="indexterm"NAME="AUTOID-43452"></A>The <EMCLASS="emphasis">nohup</EM> command ("<EMCLASS="emphasis">no h</EM>ang<EMCLASS="emphasis">up</EM>") allows you to circumvent this.(The GNU version is on the CD-ROM.)Simply type:</TD></TR></TABLE><PCLASS="para"><BLOCKQUOTECLASS="screen"><PRECLASS="screen">$ <CODECLASS="userinput"><B>nohup <CODECLASS="replaceable"><I>command</I></CODE> &</B></CODE></PRE></BLOCKQUOTE></P><PCLASS="para"><ACLASS="indexterm"NAME="AUTOID-43463"></A>Any output from <CODECLASS="replaceable"><I>command</I></CODE> that would normally go to theterminal (i.e., has not been redirected) goes to a file named <EMCLASS="emphasis">nohup.out</EM>in the current directory.</P><PCLASS="para">Of course, if you want to run jobs at off hours, you might do evenbetter using<SPANCLASS="link"><EMCLASS="emphasis">at</EM>, <EMCLASS="emphasis">cron</EM>, or <EMCLASS="emphasis">batch</EM> (<ACLASS="linkend"HREF="ch40_01.htm#UPT-ART-2313"TITLE="Off-Peak Job Submission ">40.1</A>)</SPAN>.</P><PCLASS="para"><EMCLASS="emphasis">nohup</EM> is sometimes handy in shell scripts to make them ignorethe <SPANCLASS="link">HUP and TERM signals (<ACLASS="linkend"HREF="ch38_08.htm"TITLE="What Are Signals? ">38.8</A>)</SPAN>,though <SPANCLASS="link"><EMCLASS="emphasis">trap</EM> (<ACLASS="linkend"HREF="ch44_12.htm"TITLE="Trapping Exits Caused by Interrupts ">44.12</A>)</SPAN>is more versatile.(In System V, <EMCLASS="emphasis">nohup</EM> causes a command to ignoreHUP and QUIT, but not TERM.)</P><DIVCLASS="sect1info"><PCLASS="SECT1INFO">- <SPANCLASS="authorinitials">TOR</SPAN></P></DIV></DIV><DIVCLASS="htmlnav"><P></P><HRALIGN="LEFT"WIDTH="515"TITLE="footer"><TABLEWIDTH="515"BORDER="0"CELLSPACING="0"CELLPADDING="0"><TR><TDALIGN="LEFT"VALIGN="TOP"WIDTH="172"><ACLASS="SECT1"HREF="ch38_17.htm"TITLE="38.17 Automatically Kill Background Processes on Logout in csh"><IMGSRC="gifs/txtpreva.gif"SRC="gifs/txtpreva.gif"ALT="Previous: 38.17 Automatically Kill Background Processes on Logout in csh"BORDER="0"></A></TD><TDALIGN="CENTER"VALIGN="TOP"WIDTH="171"><ACLASS="book"HREF="index.htm"TITLE="UNIX Power Tools"><IMGSRC="gifs/txthome.gif"SRC="gifs/txthome.gif"ALT="UNIX Power Tools"BORDER="0"></A></TD><TDALIGN="RIGHT"VALIGN="TOP"WIDTH="172"><ACLASS="CHAPTER"HREF="ch39_01.htm"TITLE="39. 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