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swapon(8)
NAME
swapon - Specifies additional disk partitions for paging and swapping
SYNOPSIS
/sbin/swapon [-a | -v | -p | -s | -d | -F] [-D device] [-l size] [-h
size] filename
OPTIONS
-a Installs all paging partitions specified in the /etc/sysconfigtab file.
-v Generates verbose output.
-p (Ignored on Tru64 UNIX)
Specifies the filename given in the command is the preferred paging
device.
-s Displays swap space utilization. For each swap partition, this option
displays the total amount of allocated swap space, the amount of swap
space that is being used, and the amount of free swap space.
-d Sets the first specified swap device as the system dump device,
providing the system dump device was not previously set.
-F Force the use of the specified swap device, even if either of the
following conditions are true:
· You specified a partition that is currently in use (that is, the
partition contains a valid file system).
· The device contains other file partitions that are currently in
use.
If you do not specify the -F option and the partition is in use, the
swapon command displays a partition check warning message. It then
gives you an opportunity to override the partition check.
-D device
Explicitly sets the system dump device to be the specified device, even
if the system dump device was previously set.
-l size (Ignored on Tru64 UNIX)
Specifies the low water mark.
-h size (Ignored on Tru64 UNIX)
Specifies the high water mark.
OPERANDS
special-device
Specifies the device special file name.
DESCRIPTION
The swapon command is used to specify additional disk partitions for paging
and swapping. A paging partition is a block special device. (Tru64 UNIX
does not currently support paging and swapping to a regular file. All
paging and swapping areas must be block special devices.) The swapon
command uses a priority default of 4 for block special devices. Calls to
swapon normally occur in the system multiuser state initialization.
When you make more swap space available with the swapon command, the
additional swap space is available until the system is rebooted. To make
additional swap space permanent, you must specify the swap device entry in
the /etc/sysconfigtab file.
The swapon command options can override the partition specifications in the
/etc/sysconfigtab file. You must be superuser or have the mount command
authorization to run the swapon command. System administrators and
operators (users with the sysadmin and operator command authorizations,
respectively) usually are given mount command authorization. See dop(8) for
information about giving certain users authorization to issue privileged
commands without knowing the root password.
You can use Logical Storage Manager (LSM) volumes for additional swap
space. For high system availability, you can mirror the LSM volumes. The
Logical Storage Manager manual describes how to use the swapon command to
configure an LSM mirrored volume as additional swap space.
There are two strategies for swap space allocation: immediate mode and
deferred or over-commitment mode. The two strategies differ in the point
in time at which swap space is allocated. If immediate mode is used, swap
space is allocated when modifiable virtual address space is created. If
deferred mode is used, swap space is not allocated until the system needs
to write a modified virtual page to swap space. Immediate mode is the
default swap space allocation strategy.
Immediate mode is more conservative than deferred mode because each
modifiable virtual page is assigned a page of swap space when it is
created. If you use the immediate mode of swap space allocation, you must
allocate a swap space that is at least as large as the total amount of
modifiable virtual address space that will be created on your system.
Immediate mode requires significantly more swap space than deferred mode
because it guarantees that there will be enough swap space if every
modifiable virtual page is modified.
If you use the deferred mode of swap space allocation, you must estimate
the total amount of virtual address space that will be both created and
modified, and compare that total amount with the size of your system's
physical memory. If this total amount is greater than the size of physical
memory, the swap space must be large enough to hold the modified virtual
pages that do not fit into your physical memory. If your system's workload
is complex and you are unable to estimate the appropriate amount of swap
space by using this mode, you should first use the default amount of swap
space and adjust the swap space as needed.
To determine which swap space allocation mode is being used, check the
setting of the vm-swap-eager attribute in /etc/sysconfigtab. If this value
is either not specified or set to 1, the system uses immediate swap mode.
If it is set to 0 (zero), the system uses deferred mode.
NOTES
There is no way to stop paging and swapping on a partition. It is
therefore not possible to use swap devices that can be dismounted during
system operation.
Swap space is also used during a system crash dump. In planning your swap
space allocation you should also consider your crash dump requirements.
See the System Administration manual for information on crash dumps.
ERRORS
· special-device or an overlapping partition is open. Quitting...
Explanation:
This message indicates that you tried to add a partition as a swap
device that is actively in use by UFS, AdvFS, swap, or LSM.
User Action:
Specify a different swap device.
· special-device is marked in use for fstype in the disklabel. If you
continue with the operation you can possibly destroy existing data.
CONTINUE? [y/n]
Explanation:
This message indicates that you tried to use a partition as a swap
device that is not currently in active use but is marked for use in
the disk label's partition map. For example, the partition may be
part of an LSM volume or an AdvFS domain.
User Action:
Specify a different swap device or override the warning.
If you know that the partition you specified to swapon does not
contain any data, you can choose to override the warning. In this
case, the fstype in the disk label will be modified to swap.
Note that you can use the disklabel -s command to set the fstype in
the disk label to unused for partitions that do not contain any valid
data. See disklabel(8) for more information.
· Partition(s) which overlap special-device are marked in use If you
continue with the operation you can possibly destroy existing data.
CONTINUE? [y/n]
Explanation:
This message indicates that the partition you specified is not marked
for use, but other, overlapping partitions on the disk are marked for
use.
User Action:
Specify a different swap device or override the warning.
If you override this warning, the fstype in the disk's label will be
modified. The partition you specified to swapon will be marked as in
use as a swap device and all overlapping partitions will be marked
UNUSED.
EXAMPLES
1. Entering the swapon comand with no parameters displays the following
help message:
# swapon
usage: swapon [-avpsdF] [-D device] [-l size] [-h size] filename
2. The following example shows a swap device entry in an
/etc/sysconfigtab file:
vm:
swapdevice=/dev/disk/dsk0b,/dev/disk/dsk1b
3. The following example adds the /dev/disk/dsk0b block device file as
swap space:
# swapon /dev/disk/dsk0b
4. The following example tries to add a partition that is marked for use
as a swap device:
# /usr/sbin/swapon /dev/disk/dsk11g
/dev/disk/dsk11g disk is marked in use for LSMpubl in the
disklabel.
If you continue with the operation you can possibly destroy
existing data.
CONTINUE? [y/n]
Partition g of disk dsk11 is part of a disk marked for use by LSM. If
LSM is not actively using this partition and the partition does not
contain any data, you may want to override this warning, by answering
y. In this case, partition g will be marked as swap in the disk
label.
5. The following example tries to add a partition as a swap device whose
overlapping partitions are marked for use:
# /usr/sbin/swapon /dev/disk/dsk11c
Partition(s) which overlap /dev/disk/dsk11c are marked in use.
If you continue with the operation you can possibly destroy
existing data.
CONTINUE? [y/n]
If you answer yes, partition c on disk dsk11 will be marked swap in
the disk label and all partitions that overlap c will be marked
UNUSED.
6. The following example tries to add a partition that is currently in
use as a swap device:
# /usr/sbin/swapon /dev/disk/dsk11g
/dev/disk/dsk11g or an overlapping partition is open.
Quitting...
7. The following example tries to add a partition that does not have a
disk label as a swap device:
# /usr/sbin/swapon /dev/disk/dsk11c
The disklabel for /dev/disk/dsk11c does not exist or is
corrupted.
Quitting...
See disklabel(8) for information on installing a disk label on a disk.
FILES
/sbin/swapon
Specifies the command path.
/etc/sysconfigtab
Specifies information about file systems and swap devices.
SEE ALSO
Commands: dop(8), savecore(8)
Functions: swapon(2)
Others: sys_attrs(5), sys_attrs_vm(5)
System Administration
Logical Storage Manager
Security
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