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📁 一份很好的linux入门资料
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<TITLE>BBS水木清华站∶精华区</TITLE></HEAD><BODY><CENTER><H1>BBS水木清华站∶精华区</H1></CENTER>发信人:&nbsp;reden&nbsp;(鱼&nbsp;～&nbsp;梦娜丽莎的微笑&nbsp;流星的故事),&nbsp;信区:&nbsp;Linux&nbsp;<BR>标&nbsp;&nbsp;题:&nbsp;The&nbsp;Boot&nbsp;Procedure&nbsp;<BR>发信站:&nbsp;BBS&nbsp;水木清华站&nbsp;(Wed&nbsp;Nov&nbsp;25&nbsp;01:13:49&nbsp;1998)&nbsp;<BR>&nbsp;<BR>Last&nbsp;modified:&nbsp;Thursday,&nbsp;21&nbsp;August&nbsp;1997&nbsp;15:09&nbsp;EST&nbsp;&nbsp;<BR>&nbsp;<BR>&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<BR>&nbsp;<BR>&nbsp;<BR>The&nbsp;Boot&nbsp;Procedure&nbsp;<BR>&nbsp;<BR>Bootstrapping&nbsp;is&nbsp;the&nbsp;process&nbsp;of&nbsp;starting&nbsp;up&nbsp;a&nbsp;computer&nbsp;from&nbsp;a&nbsp;halted&nbsp;or&nbsp;powered-down&nbsp;condition.&nbsp;When&nbsp;the&nbsp;computer&nbsp;is&nbsp;<BR>switched&nbsp;on,&nbsp;it&nbsp;activates&nbsp;the&nbsp;memory-resident&nbsp;code&nbsp;which&nbsp;resides&nbsp;on&nbsp;the&nbsp;CPU&nbsp;board.&nbsp;The&nbsp;normal&nbsp;facilities&nbsp;of&nbsp;the&nbsp;operating&nbsp;<BR>system&nbsp;are&nbsp;not&nbsp;available&nbsp;at&nbsp;this&nbsp;stage&nbsp;and&nbsp;the&nbsp;computer&nbsp;must&nbsp;'pull&nbsp;itself&nbsp;up&nbsp;by&nbsp;its&nbsp;own&nbsp;boot-straps'&nbsp;so&nbsp;to&nbsp;speak.&nbsp;This&nbsp;<BR>procedure&nbsp;therefore&nbsp;is&nbsp;often&nbsp;referred&nbsp;to&nbsp;as&nbsp;bootstrapping,&nbsp;also&nbsp;known&nbsp;as&nbsp;cold&nbsp;boot.&nbsp;Although&nbsp;the&nbsp;bootstrap&nbsp;procedure&nbsp;is&nbsp;<BR>very&nbsp;hardware&nbsp;dependent,&nbsp;it&nbsp;typically&nbsp;consists&nbsp;of&nbsp;the&nbsp;following&nbsp;steps:&nbsp;&nbsp;<BR>&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;The&nbsp;memory-resident&nbsp;code&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Runs&nbsp;self-test.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Probes&nbsp;bus&nbsp;for&nbsp;the&nbsp;boot&nbsp;device&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Reads&nbsp;the&nbsp;boot&nbsp;program&nbsp;from&nbsp;the&nbsp;boot&nbsp;device.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Boot&nbsp;program&nbsp;reads&nbsp;in&nbsp;the&nbsp;kernel&nbsp;and&nbsp;passes&nbsp;control&nbsp;to&nbsp;it.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Kernel&nbsp;identifies&nbsp;and&nbsp;configures&nbsp;the&nbsp;devices.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Initializes&nbsp;the&nbsp;system&nbsp;and&nbsp;starts&nbsp;the&nbsp;system&nbsp;processes.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Brings&nbsp;up&nbsp;the&nbsp;system&nbsp;in&nbsp;single-user&nbsp;mode&nbsp;(if&nbsp;necessary).&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Runs&nbsp;the&nbsp;appropriate&nbsp;startup&nbsp;scripts.&nbsp;&nbsp;<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Brings&nbsp;up&nbsp;the&nbsp;system&nbsp;for&nbsp;multi-user&nbsp;operation.&nbsp;&nbsp;<BR>&nbsp;<BR>Kernel&nbsp;<BR>&nbsp;<BR>Most&nbsp;Unix&nbsp;systems&nbsp;implement&nbsp;a&nbsp;two-stage&nbsp;loading&nbsp;process.&nbsp;During&nbsp;the&nbsp;first&nbsp;stage,&nbsp;a&nbsp;small&nbsp;boot&nbsp;program&nbsp;is&nbsp;read&nbsp;into&nbsp;<BR>memory&nbsp;from&nbsp;a&nbsp;default&nbsp;or&nbsp;specified&nbsp;device.&nbsp;It&nbsp;is&nbsp;this&nbsp;program&nbsp;that&nbsp;reads&nbsp;in&nbsp;the&nbsp;kernel&nbsp;and&nbsp;relinquishes&nbsp;the&nbsp;control&nbsp;to&nbsp;it.&nbsp;<BR>The&nbsp;path&nbsp;to&nbsp;the&nbsp;kernel&nbsp;is&nbsp;vendor-dependent.&nbsp;For&nbsp;example,&nbsp;it&nbsp;is&nbsp;/vmunix&nbsp;on&nbsp;SunOS&nbsp;4.x,&nbsp;Digital&nbsp;Unix&nbsp;and&nbsp;Ultrix,&nbsp;/kernel/unix&nbsp;<BR>on&nbsp;SunOS&nbsp;5.x,&nbsp;/hp-ux&nbsp;on&nbsp;HP-UX,&nbsp;and&nbsp;/unix&nbsp;on&nbsp;IRIX&nbsp;and&nbsp;AIX&nbsp;systems.&nbsp;&nbsp;<BR>&nbsp;<BR>One&nbsp;of&nbsp;the&nbsp;very&nbsp;first,&nbsp;probably&nbsp;the&nbsp;most&nbsp;difficult,&nbsp;tasks&nbsp;a&nbsp;system&nbsp;administrator&nbsp;must&nbsp;perform,&nbsp;is&nbsp;configuring&nbsp;the&nbsp;kernel.&nbsp;<BR>You'll&nbsp;read&nbsp;the&nbsp;details&nbsp;later&nbsp;in&nbsp;the&nbsp;sections&nbsp;dealing&nbsp;with&nbsp;the&nbsp;'Operating&nbsp;System&nbsp;Installation'.&nbsp;Once&nbsp;the&nbsp;kernel&nbsp;is&nbsp;loaded,&nbsp;it&nbsp;<BR>remains&nbsp;in&nbsp;the&nbsp;memory&nbsp;during&nbsp;the&nbsp;running&nbsp;of&nbsp;the&nbsp;system&nbsp;and&nbsp;is&nbsp;usually&nbsp;run&nbsp;in&nbsp;a&nbsp;fixed&nbsp;amount&nbsp;of&nbsp;memory.&nbsp;When&nbsp;the&nbsp;kernel&nbsp;<BR>starts,&nbsp;it&nbsp;normally&nbsp;displays&nbsp;its&nbsp;size&nbsp;and&nbsp;the&nbsp;amount&nbsp;of&nbsp;physical&nbsp;memory&nbsp;remaining&nbsp;after&nbsp;the&nbsp;kernel&nbsp;is&nbsp;loaded.&nbsp;The&nbsp;kernel&nbsp;<BR>probes&nbsp;the&nbsp;bus&nbsp;to&nbsp;locate&nbsp;the&nbsp;devices&nbsp;specified&nbsp;during&nbsp;the&nbsp;configuration,&nbsp;and&nbsp;initializes&nbsp;the&nbsp;located&nbsp;devices&nbsp;(ignoring&nbsp;those&nbsp;<BR>that&nbsp;it&nbsp;can't&nbsp;contact).&nbsp;Any&nbsp;device&nbsp;not&nbsp;detected&nbsp;and&nbsp;initialized&nbsp;during&nbsp;the&nbsp;boot&nbsp;will&nbsp;not&nbsp;be&nbsp;accessible&nbsp;to&nbsp;system&nbsp;until&nbsp;it&nbsp;is&nbsp;<BR>properly&nbsp;connected&nbsp;and&nbsp;the&nbsp;system&nbsp;is&nbsp;rebooted.&nbsp;&nbsp;<BR>&nbsp;<BR>System&nbsp;Processes&nbsp;<BR>&nbsp;<BR>The&nbsp;kernel&nbsp;identifies&nbsp;the&nbsp;root,&nbsp;swap,&nbsp;and&nbsp;dump&nbsp;devices&nbsp;and&nbsp;then&nbsp;starts&nbsp;programs&nbsp;to&nbsp;schedule&nbsp;processes,&nbsp;manage&nbsp;<BR>physical&nbsp;memory&nbsp;and&nbsp;virtual&nbsp;memory,&nbsp;and&nbsp;the&nbsp;init&nbsp;process.&nbsp;BSD&nbsp;systems&nbsp;starts&nbsp;three&nbsp;initialization&nbsp;processes;&nbsp;swapper,&nbsp;init&nbsp;<BR>and&nbsp;pagedaemon.&nbsp;On&nbsp;the&nbsp;SVR4&nbsp;systems&nbsp;the&nbsp;initialization&nbsp;processes&nbsp;include&nbsp;sched,&nbsp;init,&nbsp;and&nbsp;various&nbsp;memory&nbsp;handlers&nbsp;<BR>(except&nbsp;on&nbsp;Solaris).&nbsp;&nbsp;<BR>&nbsp;<BR>sched&nbsp;<BR>&nbsp;<BR>The&nbsp;real-time&nbsp;scheduler,&nbsp;sched,&nbsp;runs&nbsp;as&nbsp;process&nbsp;0&nbsp;on&nbsp;SVR5&nbsp;systems.&nbsp;It&nbsp;can&nbsp;be&nbsp;used&nbsp;to&nbsp;set&nbsp;priority&nbsp;for&nbsp;real-time&nbsp;<BR>processes&nbsp;so&nbsp;that&nbsp;they&nbsp;can&nbsp;be&nbsp;given&nbsp;fast&nbsp;access&nbsp;to&nbsp;the&nbsp;kernel.&nbsp;&nbsp;<BR>&nbsp;<BR>swapper&nbsp;<BR>&nbsp;<BR>The&nbsp;swapper&nbsp;daemon&nbsp;runs&nbsp;as&nbsp;process&nbsp;0&nbsp;on&nbsp;BSD&nbsp;systems.&nbsp;It&nbsp;manages&nbsp;the&nbsp;physical&nbsp;memory&nbsp;by&nbsp;moving&nbsp;process&nbsp;from&nbsp;<BR>physical&nbsp;memory&nbsp;to&nbsp;swap&nbsp;space&nbsp;when&nbsp;more&nbsp;physical&nbsp;memory&nbsp;is&nbsp;needed.&nbsp;&nbsp;<BR>&nbsp;<BR>Page&nbsp;Daemon&nbsp;<BR>&nbsp;<BR>Various&nbsp;memory&nbsp;handlers&nbsp;run&nbsp;as&nbsp;process&nbsp;2.&nbsp;When&nbsp;a&nbsp;page&nbsp;of&nbsp;virtual&nbsp;memory&nbsp;is&nbsp;accessed,&nbsp;the&nbsp;page&nbsp;table&nbsp;within&nbsp;the&nbsp;kernel&nbsp;<BR>is&nbsp;consulted&nbsp;and&nbsp;if&nbsp;necessary,&nbsp;the&nbsp;pagedaemon&nbsp;(SunOS&nbsp;4.x)&nbsp;or&nbsp;pageout&nbsp;(SunOS&nbsp;5.x)&nbsp;is&nbsp;used&nbsp;to&nbsp;move&nbsp;pages&nbsp;in&nbsp;and&nbsp;out&nbsp;of&nbsp;<BR>physical&nbsp;memory&nbsp;and&nbsp;to&nbsp;update&nbsp;page&nbsp;tables.&nbsp;Similar&nbsp;memory&nbsp;handlers&nbsp;exist&nbsp;on&nbsp;other&nbsp;SVR5&nbsp;systems.&nbsp;&nbsp;<BR>&nbsp;<BR>
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