swapon.1m (2010 09)

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swapon(1M) swapon(1M)

NAME

swapon - enable device or ﬁle system for paging

SYNOPSIS

Form 1: Enable all deﬁned swap areas

/usr/sbin/swapon -a

[-u][-t type]...

Form 2: Enable paging on speciﬁed block devices (for the current boot)

/usr/sbin/swapon

[-e -f][-p

priority ][-u] device ...

Form 3: Deﬁne the primary paging device (for subsequent boots)

/usr/sbin/swapon

[-e -f] -s

[-S start ][-L length][-u] device

Form 4: Unconﬁgure a previously set primary paging device (for subsequent boots)

/usr/sbin/swapon -R

device

Form 5: Enable ﬁle system swap (preferred form)

/usr/sbin/swapon

[-m min][-l

limit ][-r reserve ][-p priority ] directory ...

Form 6: Enable ﬁle system swap (obsolescent form)

/usr/sbin/swapon

directory [min limit reserve priority ]

DESCRIPTION

The

swapon command enables devices or ﬁle systems on which paging is to take place. swapon

com-

mand also conﬁgures primary paging device for next boot. (NOTE: the term ‘swap’ refers to an obsolete

implementation of virtual memory; HP-UX actually implements virtual memory by way of paging rather

than swapping. This command and others retain names derived from ‘swap’ for historical reasons.)

By enabling a device for paging, the device can be accessed directly (without going through the ﬁle sys-

tem) during paging activity. When a ﬁle system is enabled for paging, the device(s) on which the ﬁle

system resides are accessed indirectly through the ﬁle system. There are advantages and disadvantages

to both type of paging. Keep the following tradeoffs in mind when enabling devices or ﬁle systems for

paging.

Paging directly to a device is signiﬁcantly faster than doing so through the ﬁle system. However, the

space on the device that is allocated to paging cannot be used for anything else, even if it is not being

actively used for paging.

Paging through a ﬁle system, while slower, provides a more efﬁcient use of the space on the device.

Space that is not being used for paging in this case can be used by the ﬁle system. Paging across a net-

work to a remote machine is always ﬁle system paging.

The system begins by paging on only a single device so that only one disk is required at bootstrap time.

Calls to

swapon normally occur in the system startup script /sbin/init.d/swap_start

making all

paging space available so that the paging activity is interleaved across several disks.

Normally, the

-a option is given (see Form 1 of SYNOPSIS), causing all devices marked as swap and all

ﬁle systems marked as swapfs in the ﬁle /etc/fstab to be made available to the paging system. By

using the ﬁelds in /etc/fstab (special_ﬁle_name or directory ; see fstab (4)), the system determines

which block device or ﬁle system to use. The special_ﬁle_name speciﬁed for each swap entry must

specify a block special ﬁle. The directory speciﬁed for each swapfs entry must specify a directory within

the ﬁle system to be enabled.

In Form 2, the

-p option enables speciﬁc block devices to be used for paging for the current boot. The

device arguments must specify block special ﬁles. If more than one device is given, any options speciﬁed

will be applied to all devices.

In Form 3, the

-s option conﬁgures the block device to be used as the primary paging area for subse-

quent boots.

In either Form 2 or Form 3, if a ﬁle system exists on the speciﬁed block device and neither an

-e nor -f

option is speciﬁed, swapon fails and an error message is given. This prevents a ﬁle system from being

inadvertently destroyed. To request paging in the space between the end of the ﬁle system and the end of

the device, use -e. To force paging to a device containing a ﬁle system (destroying the ﬁle system), the

-f option can be used. Use -f with extreme caution!

HP-UX 11i Version 3: September 2010 − 1 − Hewlett-Packard Company 1

Summary of content (4 pages)

PAGE 1
swapon(1M) swapon(1M) NAME swapon - enable device or file system for paging SYNOPSIS Form 1: Enable all defined swap areas /usr/sbin/swapon -a [-u] [-t type ]... Form 2: Enable paging on specified block devices (for the current boot) /usr/sbin/swapon [-e -f] [-p priority ] [-u] device ...
PAGE 2
swapon(1M) swapon(1M) In either Form 2 or Form 3, an attempt to enable paging to a device will fail and a warning message will be issued if swapon determines that the device is being used by the savecrash command to retrieve system dump information (see savecrash (1M)). The -u option can be used to forcibly enable paging to devices being used by the savecrash command; however, this may overwrite system dump information contained on the device.
PAGE 3
swapon(1M) swapon(1M) -L length When configuring the primary paging device for next boot, length specifies the maximum number of blocks that will be used for paging. The default for length is to the end-of-device. -L length can only be specified when defining primary swap space for subsequent boots; therefore, -L must be used in conjunction with the -s option. -m min min indicates the space the paging system will initially take from the file system.
PAGE 4
swapon(1M) swapon(1M) 40MB of file system paging. /usr/sbin/swapon -l 5000 -r 10000 -p 2 /paging /usr/sbin/swapon /paging 0 5000 10000 2 This example enables paging to two block devices and sets the priority of both devices to 0. /usr/sbin/swapon -p 0 /dev/dsk/c10t0d0 /dev/dsk/c13t0d0 This example enables paging to a block device, using the space after the end of the file system for paging and letting the priority default to 1.