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MKSWAP(8) LinuxProgrammer'sManual MKSWAP(8)

NAMEmkswap-setupaLinuxswaparea

SYNOPSISmkswap[-c][-f][-pPSZ][-Llabel][-Uuuid]device[size]

DESCRIPTIONmkswapsetsupaLinuxswapareaonadeviceorinafile.

Thedeviceargumentwillusuallybeadiskpartition(somethinglike/dev/sdb7)butcanalsobeafile.TheLinuxkerneldoesnotlookatpartitionId's,butmanyinstallationscriptswillassumethatpartitionsofhextype82(LINUX_SWAP)aremeanttobeswappartitions.(Warning:Solarisalsousesthistype.BecarefulnottokillyourSolarispartitions.)

Thesizeparameterissuperfluousbutretainedforbackwardscompatibi

lity.(Itspecifiesthedesiredsizeoftheswapareain1024-byteblocks.mkswapwillusetheentirepartitionorfileifitisomitted. Specifyingitisunwise-atypomaydestroyyourdisk.)

ThePSZparameterspecifiesthepagesizetouse.Itisalmostalwaysunnecessary(evenunwise)tospecifyit,butcertainoldlibcversionslieaboutthepagesize,soitispossiblethatmkswapgetsitwrong.Thesymptomisthatasubsequentswaponfailsbecausenoswapsignatureisfound.TypicalvaluesforPSZare4096or8192.

Aftercreatingtheswaparea,youneedtheswaponcommandtostartusingit.Usuallyswapareasarelistedin/etc/fstabsothattheycanbetakenintouseatboottimebyaswapon-acommandinsomebootscript.

WARNINGTheswapheaderdoesnottouchthefirstblock.Abootloaderordisklabelcanbethere,butitisnotrecommendedsetup.TherecommendedsetupistouseaseparatepartitionforaLinuxswaparea.

mkswaplikemanyothersmkfs-likeutilserasesthefirstblocktoremove

oldon-diskfilesystems.

mkswaprefusestoerasethefirstblockonadevicewithadisklabel(SUN,BSD,...)oronwholedisk(e.g./dev/sda).

OPTIONS-cCheckthedevice(ifitisablockdevice)forbadblocksbeforecreatingtheswaparea. Ifanyarefound,thecountisprinted.

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-fForce-goaheadevenifthecommandisstupid.Thisallowsthecreationofaswaparealargerthanthefileorpartitionitresideson.

Withoutthisoptionmkswapwillrefusetoerasethefirstblockonadevicewithapartitiontableoronwholedisk(e.g./dec/sda).

-pPSZSpecifythepagesizetouse.

-LlabelSpecifyalabel,toallowswaponbylabel.(Onlyfornewstylesw

apareas.)

-v0,-v1Specifytheswapspaceversion.Thisoptionisdeprecatedand-v1

issupportedonly.

Thekernelhasnotsupportedv0swapspaceformatsince2.5.22.Thenewversionv1issupportedsince2.1.117.

-UuuidSpecifytheuuidtouse.ThedefaultistogenerateUUIDs.

NOTESThemaximumusefulsizeofaswapareadependsonthearchitectureandthekernelversion.Itisroughly2GiBoni386, PPC,m68k,ARM,1GiBonsparc,512MiBonmips,128GiBonalphaand3TiBonsparc64.Forkernelsafter2.3.3thereisnosuchlimitation.

Notethatbefore2.1.117thekernelallocatedonebyteforeachpage,whileitnowallocatestwobytes,sothattakingaswapareaof2GiBinusemightrequire2MiBofkernelmemory.

Presently,Linuxallows32swapareas(thiswas8beforeLinux2.4.10).

Theareasinusecanbeseeninthefile/proc/swaps(since2.1.25).

mkswaprefusesareassmallerthan10pages.

Ifyoudon'tknowthepagesizethatyourmachineuses,youmaybeabletolookitupwith"cat/proc/cpuinfo"(oryoumaynot-thecontentsofthisfiledependonarchitectureandkernelversion).

Tosetupaswapfile,itisnecessarytocreatethatfilebeforeinitializingitwithmkswap,e.g.usingacommandlike

#ddif=/dev/zeroof=swapfilebs=1024count=65536

Notethataswapfilemustnotcontainanyholes(so,usingcp(1)tocreatethefileisnotacceptable).

SEEALSOfdisk(8),swapon(8)

AVAILABILITY

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Themkswapcommandispartoftheutil-linux-ngpackageandisavailablefromftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

Linux 13March2009 MKSWAP(8)