/usr/share/ltsp/scripts/popularity-contest-ltsp is in ltsp-server 5.3.7-0ubuntu2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
| 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 | #!/bin/sh
# install this in the server's cron.daily to have the terminal chroot
# filesystems submit popularity-contest data
# it requires installing popularity-contest in each chroot, preferrably
# configured to use HTTP POST, introduced in popularity-contest 1.30, as this
# avoids the need for working mail in the chroot environment.
# change this if you have chroots in other locations
BASE="/opt/ltsp"
for base in $BASE ; do
    if [ -d "$BASE" ]; then
        # find all the top-level directories in $BASE
        for dir in $(find $BASE -maxdepth 1 -type d) ; do
            # only do the following if popularity-contest is installed, 
            # /bin/true exists and returns true (in case of architecture mis-match),
            # and chroot is available
            if [ -x $dir/bin/true ] && [ $dir/bin/true ] && [ -n "$(which chroot)" ] ; then
                # check for presence of cron.daily or cron.weekly script, and
                # run the first one found (popcon 1.45+ runs from cron.daily)
                for frequency in daily weekly ; do
                    script="/etc/cron.$frequency/popularity-contest"
                    if [ -x "$dir/$script" ]; then
                        if [ "$frequency" = "weekly" ] && [ "$(date +%w)" != "0" ]; then
                            # only run cron.weekly script once a week
                            break
                        fi
                        chroot $dir $script
                        break
                    fi
                done
            fi
        done
    fi
done
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