D. Allen [CGL]" <idallen@watcgl.waterloo.edu> (02/28/91)
You'll like this one; it's so simple. On Ultrix (any version), if you happen to have directories named /tmp/t1 or /tmp/t2, all kinds of nasty things will happen to your /etc/motd and /etc/gettytab because /etc/rc.local assumes it can write to these tmp names as files, and it edits the contents into your /etc/motd and /etc/gettytab. Nobody checks the error returns on any of these commands, so if the names are directories, well, you get a mess. The problem is even neater than this, since rc.local doesn't remove /tmp/t1 before writing into it, and the writing is done *before* clearing /tmp. So J.Q. Twit on your machine just makes this symlink: % ln -s /vmunix /tmp/t1 and the next time your machine reboots, your rc.local wipes out your vmunix. Actually, to be most destructive, link /tmp/t2 to /vmunix and /tmp/t1 to, say, /etc/passwd or something. Then rc.local will clobber both of them. Standard rules of (shell) programming: - pick unique names for your temp files - remove your temp files before you write into them - check all your error returns and don't barge ahead with bad data This problem with /tmp/t1 has been in every version of Ultrix since I started counting somewhere back around Ultrix 2.0-1. If DEC had an electronic SPR clearing house, you probably wouldn't be reading this now. -- -IAN! (Ian! D. Allen) idallen@watcgl.uwaterloo.ca idallen@watcgl.waterloo.edu [129.97.128.64] Computer Graphics Lab/University of Waterloo/Ontario/Canada
brendan@cs.widener.edu (Brendan Kehoe) (02/28/91)
In <1991Feb28.083356.6769@watcgl.waterloo.edu>, idallen@watcgl.waterloo.edu writes: >On Ultrix (any version), if you happen to have directories named >/tmp/t1 or /tmp/t2, all kinds of nasty things will happen to your >/etc/motd and /etc/gettytab because /etc/rc.local assumes it can write >to these tmp names as files, and it edits the contents into your >/etc/motd and /etc/gettytab. Suns have the same problem; just change the /tmp/t1 and /tmp/t2 names to /etc/t1 and /etc/t2 -- since rc.local's run as root, you'll be fine. -- Brendan Kehoe - Widener Sun Network Manager - brendan@cs.widener.edu Widener University in Chester, PA A Bloody Sun-Dec War Zone
peirce@gumby.cc.wmich.edu (Leonard Peirce) (02/28/91)
In article <1991Feb28.131938.29631@cs.widener.edu> brendan@cs.widener.edu (Brendan Kehoe) writes: >In <1991Feb28.083356.6769@watcgl.waterloo.edu>, idallen@watcgl.waterloo.edu writes: >>On Ultrix (any version), if you happen to have directories named >>/tmp/t1 or /tmp/t2, all kinds of nasty things will happen to your >>/etc/motd and /etc/gettytab because /etc/rc.local assumes it can write >>to these tmp names as files, and it edits the contents into your >>/etc/motd and /etc/gettytab. > > Suns have the same problem; just change the /tmp/t1 and /tmp/t2 > names to /etc/t1 and /etc/t2 -- since rc.local's run as root, you'll > be fine. You could just add rm -fr /tmp/t1 /tmp/t2 just before the edit to motd. I always just comment out the entire mess. I can maintain motd myself; I don't need rc.local to change it for every reboot. -- Leonard Peirce Internet: peirce@gumby.cc.wmich.edu Western Michigan University peirce@gw.wmich.edu Academic Computing Services UUCP: ...!uunet!sharkey!wmichgw!peirce Kalamazoo, MI 49008 Phone: (616) 387-5469
jch@dyfed.rdg.dec.com (John Haxby) (03/01/91)
You don't actually need these temporary files
at all. I got fed up of waiting for the edit on reboot
so I re-wrote it to look like this:
------------------------------
VERSION=`echo version\?s |
adb /vmunix - |
sed -e 1d -e 's/_version:[ \t]*//'` 2>&1 > /dev/console
if [ "$VERSION" != "" ]
then echo $VERSION
echo -n 'update /etc/motd ...'
mv /etc/motd /etc/motd.BAK
(echo $VERSION; grep -v ULTRIX /etc/motd.BAK) > /etc/motd
echo -n ' update /etc/gettytab ...'
VERSION=`echo $VERSION | sed 's/System.*//'`
(echo '/^ULTRIX.*/s//'"$VERSION"'\\'; echo w) |
ed /etc/gettytab > /dev/null
echo ' done.'
fi 2>&1 >/dev/console
---------------
(The \t is a tab). I suspect a similar thing could be done for
a mips machine (that doesn't have adb); although you could
always go back and use the slow `strings' it needs be.
--
John Haxby, Definitively Wrong.
Digital <jch@wessex.rdg.dec.com>
Reading, England <...!ukc!wessex!jch>