Slackware 13.1 - Sharing Screen sessions in Linux classrooms
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Public domain
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### SetUID for screen binary

    chmod u+s $(readlink -f $(which screen))

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### Add a restricted user

    [ ! -e /bin/rbash ] && ln -sf bash /bin/rbash
    useradd -m -s /bin/rbash students
    passwd students

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###  /home/students/.profile

    trap "" 2 3 20
    clear
    echo "Welcome to the Linux Class"
    echo "You can enter <Ctrl-a d> to detach at any time or just close your terminal"
    echo -n "Press Enter to continue..." && read
    screen -x root/linux-class
    exit

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### /home/students/.bash_profile

        source ~/.profile
 
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### /root/linux-class.sh

    #!/bin/bash
    source /etc/profile
    screen -wipe
    if ! ls /root/.screen/*linux-class* &> /dev/null; then
      screen -dmS linux-class
    fi
    TMP=$(mktemp)
    cat > ${TMP} << EOF
    multiuser on
    acladd students
    aclchg students -wx "#,?"
    aclchg students +x "detach"
    EOF
    screen -r linux-class -X source ${TMP}
    rm ${TMP}
 
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### Start and attach to linux-class session

    /root/linux-class.sh
    screen -x linux-class

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### remote access to linux-class session

    ssh students@hostname
 
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_BY: Pejman Moghadam_  
_TAG: screen, trap, suid, rbash_  
_DATE: 2011-12-10 10:06:56_