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Linux
Gentoo
Linux FAQ Items
Post 302088226 by prashant_ohol on Sunday 10th of September 2006 05:02:25 PM
09-10-2006
Linux FAQ Items
Hello Guys,
Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 64 MB to 128 MB, but there is only 128 MB of swap space. It might be advantageous to increase the amount of swap space to 256 MB if you perform memory-intense operations or run applications that require a large amount of memory.
You have two options: add a swap partition or add a swap file. The easiest way to achieve this it to through swap file.
To add a swap file:
Determine the size of the new swap file and multiple by 1024 to determine the block size. For example, the block size of a 64 MB swap file is 65536.
At a shell prompt as root, type the following command with count being equal to the desired block size:
dd if=/dev/zero of=/swapfile bs=1024 count=65536
then
mkswap /swapfile
To enable the swap file immediately but not automatically at boot time:
swapon /swapfile
To enable it at boot time, edit /etc/fstab to include:
/swapfile swap swap defaults 0 0
The next time the system boots, it will enable the new swap file.
After adding the new swap file and enabling it, make sure it is enabled by viewing the output of the command cat /proc/swaps or free.
bingo
Let me know if you have any questions.
Prashant,
prashant ohol - System Administrator,
Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 64 MB to 128 MB, but there is only 128 MB of swap space. It might be advantageous to increase the amount of swap space to 256 MB if you perform memory-intense operations or run applications that require a large amount of memory.
You have two options: add a swap partition or add a swap file. The easiest way to achieve this it to through swap file.
To add a swap file:
Determine the size of the new swap file and multiple by 1024 to determine the block size. For example, the block size of a 64 MB swap file is 65536.
At a shell prompt as root, type the following command with count being equal to the desired block size:
dd if=/dev/zero of=/swapfile bs=1024 count=65536
then
mkswap /swapfile
To enable the swap file immediately but not automatically at boot time:
swapon /swapfile
To enable it at boot time, edit /etc/fstab to include:
/swapfile swap swap defaults 0 0
The next time the system boots, it will enable the new swap file.
After adding the new swap file and enabling it, make sure it is enabled by viewing the output of the command cat /proc/swaps or free.
bingo
Let me know if you have any questions.
Prashant,
prashant ohol - System Administrator,
Last edited by prashant_ohol; 09-11-2006 at 04:50 PM..
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LEARN ABOUT OPENSOLARIS
mkswap
MKSWAP(8) System Administration MKSWAP(8) NAME
mkswap - set up a Linux swap area SYNOPSIS
mkswap [options] device [size] DESCRIPTION
mkswap sets up a Linux swap area on a device or in a file. The device argument will usually be a disk partition (something like /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. (Warning: Solaris also uses this type. Be careful not to kill your Solaris partitions.) The size parameter is superfluous but retained for backwards compatibility. (It specifies the desired size of the swap area in 1024-byte blocks. mkswap will use the entire partition or file if it is omitted. Specifying it is unwise - a typo may destroy your disk.) After creating the swap area, you need the swapon command to start using it. Usually swap areas are listed in /etc/fstab so that they can be taken into use at boot time by a swapon -a command in some boot script. 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 recom- mended setup is to use a separate partition for a Linux swap area. mkswap, like many others mkfs-like utils, erases the first partition block to make any previous filesystem invisible. However, mkswap refuses to erase the first block on a device with a disk label (SUN, BSD, ...). OPTIONS
-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. -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, mkswap will refuse to erase the first block on a device with a partition table. -L, --label label Specify a label for the device, to allow swapon by label. -p, --pagesize size Specify the page size (in bytes) to use. This option is usually unnecessary; mkswap reads the size from the kernel. -U, --uuid UUID Specify the UUID to use. The default is to generate a UUID. -v, --swapversion 1 Specify the swap-space version. (This option is currently pointless, as the old -v 0 option has become obsolete and now only -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).) -h, --help Display help text and exit. -V, --version Display version information and exit. 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 /proc/swaps 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 - the con- tents 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 mkswap, e.g. using a command like # fallocate --length 8GiB swapfile Note that a swap file must not contain any holes. Using cp(1) to create the file is not acceptable. Neither is use of fallocate(1) on file systems that support preallocated files, such as XFS or ext4, or on copy-on-write filesystems like btrfs. It is recommended to use dd(1) and /dev/zero in these cases. Please read notes from swapon(8) before adding a swap file to copy-on-write filesystems. ENVIRONMENT
LIBBLKID_DEBUG=all enables libblkid debug output. SEE ALSO
fdisk(8), swapon(8) AVAILABILITY
The mkswap command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/. util-linux March 2009 MKSWAP(8)