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#1 (**permalink**) 01-12-2008, 05:13 AM

I am currently confused on how Solaris is able to map the swap device to
the swap mount point.

Of course, swap -a lets you specify that the device / slice is for swap.

But in /etc/vfstab:

swap - /tmp tmpfs - yes -

You do not actually say that /tmp will use /dev/dsk/c0t0d0s1.
Where is the mapping of /dev/dsk/c0t0d0s1 <----> /tmp stored ?

.... or is it that you tell it what devices / slices you want to use for
swap, and Solaris will use whatever devices / slices are available for
swap when you use tmpfs ? In this case, where does Solaris store its
list of swap devices / slices ?

#2 (**permalink**) 01-12-2008, 05:14 AM

newbie wrote:
>
> I am currently confused on how Solaris is able to map the swap device to
> the swap mount point.
>
> Of course, swap -a lets you specify that the device / slice is for swap.
>
> But in /etc/vfstab:
>
> swap - /tmp tmpfs - yes -
>
>
> You do not actually say that /tmp will use /dev/dsk/c0t0d0s1.
> Where is the mapping of /dev/dsk/c0t0d0s1 <----> /tmp stored ?

You've completely misunderstood the effect of that line. The line that
sets up your swap is

/dev/dsk/c0t0d0s1 - - swap - no -

or similar. A swapfile (as opposed to a partition) would read something
like:

/export/swap - - swap - no -

What tells the startup scripts that this partition or file is to be used
as swap is the word "swap" in field 4. The script
/etc/init.d/standardmounts calls /sbin/swapadd (also a script, take a
look and see what it does) to parse /etc/vfstab and add swap
files/partitions if they're tagged as "swap" in field 4 of vfstab.

What the line you quote

> swap - /tmp tmpfs - yes -

does is different, and has absolutely nothing at all to do with adding
swap. It says "mount /tmp as a tmpfs". This means that /tmp will be
mounted in such a way that it uses swap (or more precisely uses
available VM) rather than a physical partition. See the manpages for
tmpfs, mount_tmpfs(1m) and tmpfs(7fs) to see what tmpfs is all about.

HTH

--
Tony

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