All entries for Thursday 29 April 2010

O2 Joggler shell script strangeness

Last night I took delivery of an O2 Joggler which I ordered whilst they were recently on offer for £50. The offer exhausted O2's stock so I had to wait a couple weeks for mine to arrive. I didn't buy it for what O2 advertise it as, I bought it for what is is as piece of hardware. Inside is an Intel Atom Z520, 512MB ram, 1GB of storage and a wireless adaptor. Visible on the outside are an Ethernet port, 3.5mm headphone jack, USB port and a 7" 800x480 touch screen. Oh and a small sticker indicating it's 'powered by openpeak'. It runs Linux. I've seen people say that the Linux is a cut down Ubuntu 8.04 though I've not been able to find any proof of this. It very definitely has BusyBox on there though. Put some special files on to a USB flash drive, plug it in, boot the device and you have telnet access and can mess around with it's OS. You can also make it run a different OS off a flash drive. So, a neat little box that should be fun to play with. The Joggler has been around for nearly a year so there's already several forums out there already on the subject and the recent £50 offer has inevitably fuelled interest.

So far my biggest hack is to enable ssh access to it. Next will be installing scp so I can copy files/to from it easily. Earlier on I was having a bit of a general poke around in it, looking around the filesystem, seeing what processes were running and such when I discovered an interesting script. What makes it interesting are these three functions:

numDaysInMonth()
{
  case $1 in
  1|3|5|7|8|10|12)
     echo 31
     ;;
  2) echo $((28 + leap))
     ;;
  4|6|9|11)
     echo 30
     ;;
  *) echo 0
     ;;
  esac
}

parseTime()
{
  set -- $(date "+%Y %m %d %H %M %S %Z")
  Year=$1
  CurMonth=`echo $2 | sed 's/^0//'`
  Today=`echo $3 | sed 's/^0//'`
  Hour=`echo $4 | sed 's/^0//'`
  Min=`echo $5 | sed 's/^0//'`
  Secs=`echo $6 | sed 's/^0//'`
  Timezone=$7
}

# function to get a very close approximate to the number
# of seconds since epoch for use to mark app start time
# and, upon app exit, current time. The delta of current
# to start time is used to determine if the restart should
# be tallied or not by comparing to MinAppUpTime
##
calculateEpoch()
{
  parseTime

  # leap days in past years
  ##
  leapdays=$(( (Year - 1969)/4 ))
  leap=$(( Year % 4 == 0 ))

  # days since the epoch, not counting earlier months this year
  ##
  numDays=$(( (Year - 1970) * 365 + leapdays + Today - 1))

  # step through earlier months this year and add the days
  ##
  month=$((CurMonth - 1))
  while [ ${month} -ge 1 ]; do
    numDays=$(( numDays + `numDaysInMonth $month` ))
    month=$(expr $month - 1)
  done

  # now the seconds...
  ##
  epoch=$(( ( (numDays * 24 + Hour) * 60 + Min) * 60 + Secs ))

  echo ${epoch}
}

The calculateEpoch function is later called like so:

startTime=`calculateEpoch`

I can't figure out why someone wrote all that code to get a 'close approximate', or to put it another way, incorrect, value for the number of seconds since epoch instead of using this to get the correct value:

startTime=`date +%s`

And yes, the BusyBox date function does allow that. If you happen to have a Joggler on which you've enabled shell access, the code in question appears in /openpeak/tango/xinit.sh

Mike Willis : 29 Apr 2010 21:51 |  Tags: Joggler |  Comments (0) |  Close comments |  Report a problem