diff options
Diffstat (limited to '')
| -rw-r--r-- | disk-utils/mkswap.8 | 156 |
1 files changed, 156 insertions, 0 deletions
diff --git a/disk-utils/mkswap.8 b/disk-utils/mkswap.8 new file mode 100644 index 0000000..27f9221 --- /dev/null +++ b/disk-utils/mkswap.8 @@ -0,0 +1,156 @@ +.\" Copyright 1998 Andries E. Brouwer (aeb@cwi.nl) +.\" +.\" May be distributed under the GNU General Public License +.\" +.TH MKSWAP 8 "March 2009" "util-linux" "System Administration" +.SH NAME +mkswap \- set up a Linux swap area +.SH SYNOPSIS +.B mkswap +[options] +.I device +.RI [ size ] +.SH DESCRIPTION +.B mkswap +sets up a Linux swap area on a device or in a file. + +The +.I device +argument will usually be a disk partition (something like +.IR /dev/sdb7 ) +but can also be a file. +The Linux kernel does not look at partition IDs, but +many installation scripts will assume that partitions +of hex type 82 (LINUX_SWAP) are meant to be swap partitions. +(\fBWarning: Solaris also uses this type. Be careful not to kill +your Solaris partitions.\fP) + +The +.I size +parameter is superfluous but retained for backwards compatibility. +(It specifies the desired size of the swap area in 1024-byte blocks. +.B mkswap +will use the entire partition or file if it is omitted. +Specifying it is unwise \(en a typo may destroy your disk.) + +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 a recommended setup. The recommended setup is to +use a separate partition for a Linux swap area. + +.BR mkswap , +like many others mkfs-like utils, +.B erases the first partition block to make any previous filesystem invisible. + +However, +.B mkswap +refuses to erase the first block on a device with a disk +label (SUN, BSD, \&...\&). + +.SH OPTIONS +.TP +.BR \-c , " \-\-check" +Check the device (if it is a block device) for bad blocks +before creating the swap area. +If any bad blocks are found, the count is printed. +.TP +.BR \-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. + +Also, without this option, +.B mkswap +will refuse to erase the first block on a device with a partition table. +.TP +.BR \-L , " \-\-label " \fIlabel\fR +Specify a \fIlabel\fR for the device, to allow +.B swapon +by label. +.TP +.BR \-p , " \-\-pagesize " \fIsize\fR +Specify the page \fIsize\fR (in bytes) to use. This option is usually unnecessary; +.B mkswap +reads the size from the kernel. +.TP +.BR \-U , " \-\-uuid " \fIUUID\fR +Specify the \fIUUID\fR to use. The default is to generate a UUID. +.TP +.BR \-v , " \-\-swapversion 1" +Specify the swap-space version. (This option is currently pointless, as the old +.B \-v 0 +option has become obsolete and now only +.B \-v 1 +is supported. +The kernel has not supported v0 swap-space format since 2.5.22 (June 2002). +The new version v1 is supported since 2.1.117 (August 1998).) +.TP +.BR \-h , " \-\-help" +Display help text and exit. +.TP +.BR \-V , " \-\-version" +Display version information and exit. + +.SH NOTES +The maximum useful size of a swap area depends on the architecture and +the kernel version. + +The maximum number of the pages that is possible to address by swap area header +is 4294967295 (UINT_MAX). The remaining space on the swap device is ignored. + +Presently, Linux allows 32 swap areas. +The areas in use can be seen in the file +.I /proc/swaps + +.B mkswap +refuses areas smaller than 10 pages. + +If you don't know the page size that your machine uses, you may be +able to look it up with "cat /proc/cpuinfo" (or you may not \(en +the contents of this file depend on architecture and kernel version). + +To set up a swap file, it is necessary to create that file before +initializing it with +.BR mkswap , +e.g.\& using a command like + +.nf +.RS +# dd if=/dev/zero of=swapfile bs=1MiB count=$((8*1024)) +.RE +.fi + +to create 8GiB swapfile. + +Note that a swap file must not contain any holes. Using +.BR cp (1) +to create the file is not acceptable. Neither is use of +.BR fallocate (1) +on file systems that support preallocated files, such as +.BR XFS " or " ext4 , +or on copy-on-write filesystems like +.BR btrfs . +It is recommended to use +.BR dd (1) +and /dev/zero in these cases. Please read notes from +.BR swapon (8) +before adding a swap file to copy-on-write filesystems. + +.SH ENVIRONMENT +.IP LIBBLKID_DEBUG=all +enables libblkid debug output. + +.SH "SEE ALSO" +.BR fdisk (8), +.BR swapon (8) +.SH AVAILABILITY +The mkswap command is part of the util-linux package and is available from +https://www.kernel.org/pub/linux/utils/util-linux/. |