Re: 5.x: how do I get a *swap*-backed /tmp via rc.conf?

From: Malcolm Kay (malcolm.kay_at_internode.on.net)
Date: 10/10/05

  • Next message: David Wolfskill: "Re: 5.x: how do I get a *swap*-backed /tmp via rc.conf?" 
    To: stable@freebsd.org
Date: Tue, 11 Oct 2005 00:25:34 +0930

    On Mon, 10 Oct 2005 11:37 am, David Wolfskill wrote:
    > I made the somewhat unexpected discovery that in FreeeBSD
    > 5-STABLE, if I use the "tmp*" variables in /etc/rc.conf to
    > have an MFS /tmp created, it is apparentyly not swap-backed --
    > as I expected from the part of the mdmfs man page that reads:
    >
    > By default, mdmfs creates a swap-based (MD_SWAP) disk
    > with soft-updates enabled and mounts it on mount-point.
    >
    > and a review of the way mdmfs is invoked by /etc/rc; rather,
    > it appears to be malloc-backed.
    >
    > Here's what's in /etc/{defaults/,}rc.conf about it on one such
    > machine:
    >
    > g1-59(5.4-S)[42] grep tmp /etc/{default*/,}rc.conf
    > /etc/defaults/rc.conf:tmpmfs="AUTO" # Set to YES
    > to always create an mfs /tmp, NO to never
    > /etc/defaults/rc.conf:tmpsize="20m" # Size of mfs
    > /tmp if created /etc/defaults/rc.conf:tmpmfs_flags="-S" #
    > Extra mdmfs options for the mfs /tmp
    > /etc/defaults/rc.conf:isdn_traceflags="-f /var/tmp/isdntrace0"
    > # Flags for isdntrace
    > /etc/defaults/rc.conf:clear_tmp_enable="NO" # Clear /tmp
    > at startup. /etc/rc.conf:tmpmfs="YES"
    > /etc/rc.conf:tmpsize="512m"
    > /etc/rc.conf:tmpmfs_flags="-i4096"
    > g1-59(5.4-S)[43]
    >

    These paramaters are used by the startup script /etc/rc.d/tmp
    which calls mount_md defined in /etc/rc.subr which specifically
    adds the _M (malloc) option to the mdmfs call.

    You'll need to invoke your own script (or; not so nice;
    edit rc.subr).

    Malcolm

    > And:
    >
    > g1-59(5.4-S)[43] sudo mdconfig -l -u md0
    > md0 malloc 524288 KBytes
    > g1-59(5.4-S)[44]
    >
    > Oh, for some sense of what we're working with:
    >
    > g1-59(5.4-S)[44] uname -a
    > FreeBSD g1-59.catwhisker.org. 5.4-STABLE FreeBSD 5.4-STABLE
    > #6: Sun Oct 9 06:24:17 PDT 2005
    > root@g1-59.catwhisker.org.:/usr/obj/usr/src/sys/LAPTOP i386
    > g1-59(5.4-S)[45]
    >
    > So, back to my original question: how do I get a
    > *swap*-backed /tmp?
    >
    > [The way I was alerted to the possibliity that my /tmp might
    > not be swap-backed is that I was using a machine running
    > 5-STABLE as a CVS server, in order to update /usr/ports on
    > another machine. That's why I have the -i4096 argument in
    > there, BTW: to double the number of inodes for when the CVS
    > server starts consuming them with wild abandon as it builds an
    > isomorphic hierarchy to /usr/ports in /tmp. I think it only
    > took me 3 panics before I poked around in the mailing list
    > archives and noted scottl's comment about using a swap-backed
    > /tmp instead, which got me wondering what backing store my
    > /tmp was using. I did look at /etc/rc.d/tmp, as well a
    > /etc/rc.subr, but I'm still failing to see why I'm getting a
    > malloc-backed /tmp. FWIW, although the /tmp in question is an
    > MFS in 4.x, I do this (use the box as a CVS server for
    > /usr/ports) without problem on 4.x.]
    >
    > (I don't need separate copies of any replies; I read -stable,
    > so I set Reply-To as an appropriate hint.)
    >
    > Thanks.
    >
    > Peace,
    > david
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