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| -rw-r--r-- | disk-utils/mkswap.8 | 131 |
1 files changed, 58 insertions, 73 deletions
diff --git a/disk-utils/mkswap.8 b/disk-utils/mkswap.8 index 2f4053137..44ec8fd35 100644 --- a/disk-utils/mkswap.8 +++ b/disk-utils/mkswap.8 @@ -3,7 +3,7 @@ .\" May be distributed under the GNU General Public License .\" Rewritten for 2.1.117, aeb, 981010. .\" -.TH MKSWAP 8 "25 March 1999" "Linux 2.2.4" "Linux Programmer's Manual" +.TH MKSWAP 8 "13 March 2009" "Linux" "Linux Programmer's Manual" .SH NAME mkswap \- set up a Linux swap area .SH SYNOPSIS @@ -12,26 +12,16 @@ mkswap \- set up a Linux swap area .B mkswap sets up a Linux swap area on a device or in a file. -(After creating the swap area, you need the -.B swapon -command to start using it. Usually swap areas are listed in -.I /etc/fstab -so that they can be taken into use at boot time by a -.B swapon -a -command in some boot script.) - The .I device argument will usually be a disk partition (something like -.I /dev/hda4 -or .IR /dev/sdb7 ) but can also be a file. The Linux kernel does not look at partition Id's, but many installation scripts will assume that partitions of hex type 82 (LINUX_SWAP) are meant to be swap partitions. -(Warning: Solaris also uses this type. Be careful not to kill -your Solaris partitions.) +(\fBWarning: Solaris also uses this type. Be careful not to kill +your Solaris partitions.\fP) The .I size @@ -53,30 +43,62 @@ fails because no swap signature is found. Typical values for .I PSZ are 4096 or 8192. -Linux knows about two styles of swap areas, old style and new style. -The last 10 bytes of the first page of the swap area distinguishes -them: old style has `SWAP_SPACE', new style has `SWAPSPACE2' as -signature. - -In the old style, the rest of this first page was a bit map, -with a 1 bit for each usable page of the swap area. -Since the first page holds this bit map, the first bit is 0. -Also, the last 10 bytes hold the signature. So, if the page -size is S, an old style swap area can describe at most -8*(S-10)-1 pages used for swapping. -With S=4096 (as on i386), the useful area is at most 133890048 bytes -(almost 128 MiB), and the rest is wasted. -On an alpha and sparc64, with S=8192, the useful area is at most -535560992 bytes (almost 512 MiB). - -The old setup wastes most of this bitmap page, because zero bits -denote bad blocks or blocks past the end of the swap space, -and a simple integer suffices to indicate the size of the swap space, -while the bad blocks, if any, can simply be listed. Nobody wants -to use a swap space with hundreds of bad blocks. (I would not even -use a swap space with 1 bad block.) -In the new style swap area this is precisely what is done. +After creating the swap area, you need the +.B swapon +command to start using it. Usually swap areas are listed in +.I /etc/fstab +so that they can be taken into use at boot time by a +.B swapon -a +command in some boot script. + +.SH WARNING +The swap header does not touch the first block. A boot loader or disk label +can be there, but it is not recommended setup. The recommended setup is to +use a separate partition for a Linux swap area. + +.B mkswap like many others mkfs-like utils erases the first block to remove +.B old on-disk filesystems. + +.B mkswap +refuses to erase the first block on a device with a disk +label (SUN, BSD, ...) or on whole disk (e.g. /dev/sda). + +.SH OPTIONS +.TP +.B \-c +Check the device (if it is a block device) for bad blocks +before creating the swap area. +If any are found, the count is printed. +.TP +.B \-f +Force - go ahead even if the command is stupid. +This allows the creation of a swap area larger than the file +or partition it resides on. + +Without this option +.B mkswap +will refuse to erase the first block on a device with a partition table or on +whole disk (e.g. /dec/sda). +.TP +.BI "\-p " PSZ +Specify the page size to use. +.TP +.BI "\-L " label +Specify a label, to allow swapon by label. +(Only for new style swap areas.) +.TP +.B \-v0, \-v1 +Specify the swap space version. This option is deprecated and \-v1 is +supported only. + +The kernel has not supported v0 swap space format since 2.5.22. The new version +v1 is supported since 2.1.117. + +.TP +.B \-U uuid +Specify the uuid to use. The default is to generate UUIDs. +.SH NOTES The maximum useful size of a swap area depends on the architecture and the kernel version. It is roughly 2GiB on i386, PPC, m68k, ARM, 1GiB on sparc, 512MiB on mips, @@ -114,43 +136,6 @@ Note that a swap file must not contain any holes (so, using .BR cp (1) to create the file is not acceptable). -.SH OPTIONS -.TP -.B \-c -Check the device (if it is a block device) for bad blocks -before creating the swap area. -If any are found, the count is printed. -.TP -.B \-f -Force - go ahead even if the command is stupid. -This allows the creation of a swap area larger than the file -or partition it resides on. -On SPARC, force creation of the swap area. -Without this option -.B mkswap -will refuse to create a v0 swap on a device with a valid SPARC superblock, -as that probably means one is going to erase the partition table. -.TP -.BI "\-p " PSZ -Specify the page size to use. -.TP -.BI "\-L " label -Specify a label, to allow swapon by label. -(Only for new style swap areas.) -.TP -.B \-v0, \-v1 -Specify the swap space version. This option is deprecated and \-v1 is -supported only. - -The kernel has not supported v0 swap space format since 2.5.22. The new version -v1 is supported since 2.1.117. - -The new v1 style header does not touch the first block, so may be -preferable, in case you have a boot loader or disk label there. - -.TP -.B \-U uuid -Specify the uuid to use. The default is to generate UUIDs. .SH "SEE ALSO" .BR fdisk (8), |