udp: Insist on only one successful default socket setup

[secnet] / setup.mac

#!/bin/bash
#
# Richard Kettlewell 2011-06-18
#
set -e

group=${group:-secnet}
user=${user:-secnet}

# pick ID1 ID2 ... IDn
# Echoes an ID matching none of ID1..IDn
pick() {
  local n
  n=250				# better not choose 0!
  while :; do
    ok=true
    for k in "$@"; do
      if [ $n = $k ]; then
        ok=false
        break
      fi
    done
    if $ok; then
      echo $n
      return
    fi
    n=$((1+$n))
  done
}

if dscl . -read /Groups/$group >/dev/null 2>&1; then
  :
else
  gids=$(dscl . -list /Groups PrimaryGroupID|awk '{print $2}')
  gid=$(pick $gids)
  dscl . -create /Groups/$group
  dscl . -create /Groups/$group PrimaryGroupID $gid
  dscl . -create /Groups/$group Password \*
fi

if dscl . -read /Users/$user >/dev/null 2>&1; then
  :
else
  uids=$(dscl . -list /Users UniqueID|awk '{print $2}')
  uid=$(pick $uids)
  gid=$(dscl . -read /Groups/$group PrimaryGroupID | awk '{print $2}')
  dscl . -create /Users/$user
  dscl . -create /Users/$user UniqueID $uid
  dscl . -create /Users/$user UserShell /usr/bin/false
  dscl . -create /Users/$user RealName 'secnet'
  dscl . -create /Users/$user NFSHomeDirectory /var/empty
  dscl . -create /Users/$user PrimaryGroupID $gid
  dscl . -create /Users/$user Password \*
fi

cp uk.org.greenend.secnet.plist /Library/LaunchDaemons/.
launchctl load /Library/LaunchDaemons
echo "To start secnet:"
echo "  sudo launchctl start uk.org.greenend.secnet"
echo
echo "To stop secnet:"
echo "  sudo launchctl stop uk.org.greenend.secnet"
echo
echo "To uninstall:"
echo "  sudo launchctl unload /Library/LaunchDaemons/uk.org.greenend.secnet.plist"
echo "  sudo rm -f /Library/LaunchDaemons/uk.org.greenend.secnet.plist"