A real hack way to "lock my tty"

[Brad Appleton]

In article <2874 at idunno.Princeton.EDU> pfalstad at phoenix.Princeton.EDU (Paul John Falstad) writes:
>In article <2863 at litchi.bbn.com> rsalz at bbn.com (Rich Salz) writes:
>>This only works in C-shell derivatives.  Type "goto <SomePassword>" and
>>then enough blank lines to clear the screen.
>>
>>When you come back, type "<SomePassword>:" and RETURN.
>
>I hope someone tries that at my site so I can type control-D and then
>poke around in his account until he comes back to his terminal.
>
>>As an interesting exercise, type the following lines
>>	foo:
>>	csh
>>	exit
>>	goto foo
>
>Interesting.  You can break out of it with kill -STOP $$.
>
>If Lafontaine's elk would spurn Tom Jones, the engine must be our head, the
>dining car our esophagus, the guardsvan our left lung, the kettle truck our
>shins, the first class compartment the piece of skin at the nape of the neck,
>and the level crossing an electric elk called Simon.

Ive been using the following lock-script for several years without any problems:

NOTE: you will need to physically change all '^M's in the script to be
      CTRL-M (literally). I changed it to '^' 'M' for the sake of posting
      (and worrying it might get lost in translation).
--------------------------------------------------------------------------------
#!/bin/sh
#
#   lock - Bourne Shell lockscreen utility
#
#   Created 5/19/88 by Brad Appleton
#
USAGE="usage:  lock  [-p] [-b]  [-f [filename] ]"
#
#           -p         set-up a password for future uses of lock
#           -f         get lock-message from file (or use default)
#           -b         use Banner to display lock message
#
# if -f is not given then the lock message is taken from the command
# line ("SCREEN LOCKED" is displayed if no args are given).
#
# The -p option need only be used the first time lock is invoked.
# It will ask for a password, prompt for verification, then write it
# to a hidden file with owner-read-only permission. This file is
# used to get the password for all following invocations of lock
# (unless of course you use -p to reset the password).
#
# NOTE
# ====
#       Once the screen is locked you must press a PHYSICAL LINEFEED 
#       to get prompter for the user password. Return will not do it
#       since the keyboard is in raw mode to disable suspend signals.
#       (some signals can be caught by trap, others cant).
#
trap '' 1 2 3 14 15		## turn off keyboard interrupts

set -- `getopt fpb $*`		## parse command options (using getopt - yuck!)

for i in $* ; do		## cycle thru opts
  case $i in
	-f)	fFLAG="TRUE" ; shift;;
	--)	shift; break;;
	-p)	pFLAG="TRUE" ; shift;;
	-b)	bFLAG="TRUE" ; shift;;
  esac
done

if [ "$fFLAG" ] ; then		## get name of file to display
  if [ $# -gt 0 ] ; then
    filename=$1
    shift
  else
    filename="$HOME/.msgfile"
  fi	## if args
fi  ## if -f

stty -echo			## turn echo mode off

if [ "$pFLAG" ] ; then		## now get password
  echo "\nEnter password for locking: "
  pw=`line`
  echo "\nRetype password for verification: "
  verify=`line`

  if [ ! "$pw" = "$verify" ] ; then
    echo "+++ Mismatch - no password created +++"
    stty echo -raw		## turn echo mode back on (kill raw mode)
    exit 1
  else				## create password file
    cat > $HOME/.lockpw <<EOD
$pw
EOD
    chmod 600 $HOME/.lockpw	## restrict access to password file
  fi
else
  if [ ! -f $HOME/.lockpw ] ; then	## no password -- abort
    stty echo -raw
    echo "\nlock: use the -p option to create a password.\n\n$USAGE\n"
    exit 1
  fi
fi	## if -p

if [ $# -eq 0 ] ; then		## get message to display
  mesg="SCREEN LOCKED"
else
  mesg="$*"
fi

stty raw 		## turn raw mode on to disable ^Z and ^Y
done="FALSE"		## set loop condition

while [ "$done" = "FALSE" ]; do		## display message
  clear
  if [ "$fFLAG" = "TRUE"  -a  -f "$filename" ] ; then
    sed 's/$/^M/' $filename	## hardcode those linefeeds
  elif [ "$bFLAG" = "TRUE" ] ; then
    banner $mesg | sed 's/$/^M/'
  else
    echo "^M\n^M\n^M\n^M\n^M\n^M\n^M\n^M\n"
    echo "                        $mesg^M"
  fi

  read input			## wait for a linefeed

  echo "^M\nEnter Password: ^M\n"	## get password
  read input

  pw=`cat $HOME/.lockpw`	## validate password"
  if [ "$input" = "$pw" \
		-o  "$input" = "$pw^M"	\
		-o  "$input" = "$pw^M^M"  ] ; then
    done="TRUE"
  else
    echo "^M\n+++ Password Incorrect +++"
    sleep 1
  fi
done

stty echo -raw		## reset terminal
clear
exit
______________________ "And miles to go before I sleep." ______________________
 Brad Appleton        brad at travis.ssd.csd.harris.com   Harris Computer Systems
                          ...!uunet!hcx1!brad          Fort Lauderdale, FL USA
~~~~~~~~~~~~~~~~~~~~ Disclaimer: I said it, not my company! ~~~~~~~~~~~~~~~~~~~