增加,修改 Linux 交换空间

Itallhappenssometime:yourunoutofyourmainmemoryandthesystemturnstotheharddisktouseasatemporarymemory.WhatifyoucometothelimitsofyourLinuxserver’sswapspacebutthesystemdemandsmore?Therearebasicallyfouroptionshere:

1.Createanewswapfile

2.Createaswapfileonanexistinglogicalvolume

3.Extendaswapfileonanexistinglogicalvolume

4.Createanewswappartition

Ifyouareinneedofswapspacenowanddonotthinkyouwillneeditlater,thentakingthesystemdownforcreatinganewswappartitionorextendingtheswapfileonthelogicalvolumewillbethelongerwaytotake;creatinganewswapfileandmakingitavailablewillbetheeasiestandthequickestsolution.So,inourlist,creatinganewswapfileistheeasiest,extendingswapfileonanexistinglogicalvolumeisalittleharderbutrecommended,andcreatinganewswappartitionisthehardest.

CreateaNewSwapFile

Weneedtoknowthesizeoftheadditionalswapspacewewillneed.Let’sassumethatwewillneeda512Megabytesofswapspace.Todeterminethenumberofblocks,weneedtomultiplythesizewith1024.Inourexamplethisgives512x1024=524288.Nowweissue

ddif=/dev/zeroof=/home/swapfilebs=1024count=524888

toopenupourfreespace(youmayarguethatmakingaswapspaceinthe/homedirectoryisquestionableintermsofsecurity,butifyou’retightonharddiskspaceontheserver,/homeisthedirectorythatyoucanfindsomefreespace).Thensetupthefileasswapwith

mkswap/home/swapfile

Theswapspacewillnotbeenabledatboottime.Youneedtoaddthespaceto/etc/fstab.Addthefollowinglinetoyour/etc/fstab:

/home/swapfileswapswapdefaults00

CreatingaSwapFileonanExistingLogicalVolume

Inthiscase,let’sassumewewanttoaddtheswapspaceon/dev/VolGroup00and/LogVol02istheswapspacewewanttoadd.Let’salsoassumethattheswapspaceweneedis2Gigabytes.First,wecreatethelogicalvolumeofsize2GBby

lvmlvcreateVolGroup00-nLogVol02-L2G

Thenweformatitby

mkswap/dev/VolGroup00/LogVol02

andadditto/etc/fstabbyaddingthisline:

/dev/VolGroup00/LogVol02swapswapdefaults00

Nowweactivatetheswapvolumeby

swapon-va

Tocheckiftheswapisworkingproperly,youcanissuecat/proc/swapsorsimplyfree.

Readonforextendingaswapfileonanexistinglogicalvolumeandcreatinganewpartition.

ExtendingSwapFileonanExistingLogicalVolume

Forthiscase,let’sassumethattheswapspacewewillextendis/dev/VolGroup00/LogVol01andwewanttoextenditby1Gigabyte.First,wedisabletheactiveswapfileby

swapoff-v/dev/VolgGroup00/LogVol01

Thenweaddtheswapspaceby

lvmlvresize/dev/Volgroup00/LogVol01-L1G

formatit

mkswap/dev/VolGroup00/LogVol01

andfinallyenabletheextendedvolumebyswapon-va.Asalways,youcancheckthenewspacebycat/proc/swapsorfreecommands.

CreateaNewSwapPartition

Wecangowiththepartedprogramheresinceitiseasierthanfdisk.Beforeaddingaswappartition,wehavetocheckwhichharddiskhassufficientspacetobeusedasswap.Wecandothatbyissuingprintatthepartedprompt.Withtheinformationwereceive,wedeterminehowmuchspacewewilluseandatwhatpartition.Assumethatwewilladd1GBofswapspaceto/dev/hdc1.Thesyntaxthatwewilluseinpartedis

mkpartfspartition-typefilesystem-typestartend

wherestartandendarethemegabytesfromthebeginningofthedisk(partition-typecanbeprimary,extendedorlogicalbutextendedandlogicalareusedonlyforMS-DOSandMIPSlabels).Furtherassumingthatthefreespaceon/dev/hdc1startsatthe520thmegabyte,theendingwillbe520+1024(1Gigabyteofspace)=1544.Soourcommandwillbe

mkpartfsprimarylinux-swap5201024

Afterreservingthespace,weformatitwithswappartitiontype,using

mkswap/dev/hdc1

Thenweenableitbyswapon/dev/hdc1.Andfinally,toactivateitinboottime,weadditto/etc/fstabbyaddingthefollowingline:

/dev/hdc1swapswapdefaults00

Aswehaveseen,wechecktheswapbycat/proc/swapsorfree.

Conclusion

Withthefallingpricesofmainmemoriy(RAM),usuallysystemadministratorsdonotneedtheswapspaceindailynormaloperations.Buttimescanbetoughandthesystemmayrunoutofswapspace,andthentheadministratorcanhavenochancebuttoincreaseswapsizeinordertocopewiththepeakload.Thequickestwaycouldbetoaddaswapfileandthelong-termsolutionistoaddaswappartition.

RelatedReading

HowtoBuildaLinuxServerhttp://www.brighthub.com/computing/linux/articles/29541.aspx-InthisserieswelookatbuildingandconfiguringaLinuxserverfromscratch.Wewilllookatconfigurationindetailandwewilldeterminewaystokeepourserverassecureaspossible.

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