If for example three people are running the same program simultaneously there are three processes there not just one In fact we might have more than one process running even with only person executing the program because you will see later the progr ID: 27205
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2DeterminingInformationAboutCurrentProcessesThe`ps-x'commandwilllistallyourcurrently-runningjobs.Anexampleis:PIDTTSTATTIMECOMMAND6799coIW0:01-csh[rich](csh)6823coIW0:00/bin/sh/usr/bin/X11/startx6829coIW0:00xinit/usr/lib/X11/xinit/xinitrc--6830coS0:12X:06836coI0:01twm6837coI0:01xclock-geometry50x50-1+16841p0I0:01-sh[richonxterm](csh)6840p1I0:01-sh[richonxterm](csh)6842p2S0:01-sh[richonlogin](csh)6847p2R0:00ps-xThemeaningofthecolumntitlesisasfollows:PIDprocessidentificationnumberTTcontrollingterminaloftheprocessSTATstateofthejobTIMEamountofCPUtimetheprocesshasacquiredsofarCOMMANDnameofthecommandthatissuedtheprocessTheTTinformationgivesterminalnames,whichyoucanseebytypingthewhocommand.E.g.weseep2intheTTcolumnabove,whichistheterminallistedasttyp2inthewhocommand.Thestateofthejobisgivenbyasequenceoffourletters,forexample,`RWNA'.Therstofthesefouristypicallyoneofthefollowing:rstletterrunnabilityoftheprocessRrunnableprocessTstoppedprocessSprocesssleepingforlessthanabout20secondsIprocessesthatareidle(sleepinglongerthanabout20seconds)Astate-Rprocessisrunnable,i.e.itisbeabletomakeuseofaturngiventoit,andiswaitingforone.WecanputaprocessinstateT,i.e.stoptheprocess,bytypingcontrol-z.Suppose,forexample,thatIamusingftptogetsomelesfromsomearchivesite,andInoticealetherecalledREADME.Icanusetheftp`get'commandtogettheREADMEle,andthentypeC-z.Thiswillstop(suspend)theftpprocess,andgetmebacktotheC-shell.AtthatpointIcanreadtheREADMEle,sayusingmore,andthenreactivatetheftpprocess,bytyping`fg'totheshell.AtypicalexampleofanS/Iprocessisonethatiswaitingforuserinput.IfIamusingtheemacseditor,forexample,theprocesswillgotostateSwhenitiswaitingformetotypesomething;ifItakemorethan20secondstodecidewhattotype,theprocesswillbeinstateI. signalstotheCPUatperiodicintervals.ThesesignalsforcetheCPUtostoptheprogramitisrunning,andjumptoanotherprogram,whichwillbetheoperatingsystemprogram(OS).TheOScanthendeterminewhetherthecurrentprogram'stimesliceisnished,andifso,thengiveaturntoanotherprogram,byjumpingtothatprogram.Notetheinteractionofhardware(theelectricalsignals,andtheCPU'sreactiontothem)andsoftware(theOS)here.2 [1]Doneccbigprog.cBytheway,ifyoulogout,whateverbackgroundprocessesyouhaverunningatthetimewillnot bekilled;theywillcontinuetorun.4TerminatingaProcessWecanterminateaprocessbyusingthekillcommand.Wesimplynditspid(saybyusingps),andthentypekill-9pidIftheprocessisintheforeground,though,theeasiestwaytokillitistosimplytypecontrol-C.4