Re: abusing mfs to make read-only

["Steven M. Bellovin" <smb%cs.columbia.edu@localhost>]

On Mon, 7 May 2007 23:29:07 -0400
"matthew sporleder" <msporleder%gmail.com@localhost> wrote:

> In an effort to save my CF card some writes, I added this to my fstab:
> /dev/wd0b       /var/run mfs rw,-s1m 0 0
> /dev/wd0b       /var/log mfs rw,-s10m 0 0
> 
> (I would use tmpfs, but this is 3.1)
> 
> and then modified /etc/rc.d/syslogd like so: (in syslogd_precmd())
>         #       Touch files in syslog.conf -- MSPO
>         if [ -f /etc/syslog.conf ]; then
>                 awk '{ if (($2 ~ /^\/var/) && ($0 !~ /^#/))
> { system("touch " $2 ); } }' /etc/syslog.conf
>         fi
>         #       END MSPO
>         return 0
> 
> This should boot and read from the CF card like normal (I'm not using
> a crunchgen here) and then set the only places I write to be in
> memory.
> 
> Can anyone think of another place writes might happen?
> 
/dev, for device accesses?

I have all of /var on mfs, because of things like dhcpd refreshes.  I
should, I suppose, copy those files to the real dhcpd.leases file.

In fact, I use the following script I found in a how-to:

#!/bin/sh
#
# mount_mfs_fs: mount memory file system /var and /dev
# by roby, 23 jun 2003

# PROVIDE: mount_mfs_fs
# REQUIRE: root

$_rc_subr_loaded . /etc/rc.subr

name="mount_mfs_fs"
start_cmd="mount_mfs_fs_start"
stop_cmd=":"

mount_mfs_fs_start()
{
        #       Mount /dev fs
        #
#X      echo "Mounting memory file system: /dev:"
#X      mount /dev
        #
        # build device files
#X      (cd /dev && /MAKEDEV all)

        #       Mount /var fs
        #
        echo "Mounting memory file system: /var:"
        mount /var
        #
        # build dir/files in var
        cd /
        tar -xzpf /var-image.tar.gz -C /
        echo "Mounting memory file systems: Done."
}

load_rc_config $name
run_rc_command "$1"