swapon(8)swapon(8)NAMEswapon - 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
Installs all paging partitions specified in the /etc/sysconfigtab file.
Generates verbose output. Specifies the filename given in the command
is the preferred paging device. 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. Sets the first specified swap device as the system
dump device, providing the system dump device was not previously set.
Force the use of the specified swap device, even if either of the fol‐
lowing 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. Explicitly sets the system dump device to be the speci‐
fied device, even if the system dump device was previously set.
Specifies the low water mark. Specifies the high water mark.
OPERANDS
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 authoriza‐
tions, 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 com‐
mand 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. Imme‐
diate 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 esti‐
mate the total amount of virtual address space that will be both cre‐
ated 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 dur‐
ing 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 require‐
ments. 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 oper‐
ation 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. Parti‐
tion(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
Entering the swapon comand with no parameters displays the following
help message: # swapon usage: swapon [-avpsdF] [-D device] [-l size]
[-h size] filename The following example shows a swap device entry in
an /etc/sysconfigtab file:
vm:
swapdevice=/dev/disk/dsk0b,/dev/disk/dsk1b The following
example adds the /dev/disk/dsk0b block device file as swap
space: # swapon /dev/disk/dsk0b 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 parti‐
tion 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. 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. 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. Quit‐
ting... 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 cor‐
rupted. Quitting...
See disklabel(8) for information on installing a disk label on a
disk.
FILES
Specifies the command path. 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
swapon(8)
