Generate time serie in iso-8601 format using date command, how to deal with server system date origin offset?

Question

I have the following bash function that generate an epoch list in iso-8601 format on a machine that runs ubuntu and it works fine. (where isdate and isint bash functions to test the input)

gen_epoch()
{
 #@ USAGE: gen_epoch [start_date_iso] [end_date_iso] [increment_in_seconds]
 #@
 #@ TASK : generate an epoch list (epoch list in isodate format).
 #@        result on STDOUT:               [epoch_list]
 #@        error_code      :  2             0

 ## test argument
 if [ "$#" -ne 3 ]; then echo "$FUNCNAME: input error [nb_of_input]"; return 2
 elif [ $( isdate $1 &> /dev/null; echo $? ) -eq 2 ]; then echo "$FUNCNAME: argument error [$1]"; return 2
 elif [ $( isdate $2 &> /dev/null; echo $? ) -eq 2 ]; then echo "$FUNCNAME: argument error [$2]"; return 2
 elif [ $( isint $3 &> /dev/null; echo $? ) -eq 2 ]; then echo "$FUNCNAME: argument error [$3]"; return 2
 else local beg=$( TZ=UTC date --date="$1" +%s ); local end=$( TZ=UTC date --date="$2" +%s ); local inc=$3; fi

 ## generate epoch
 while [ $beg -le $end ]
 do
  local date_out=$( TZ=UTC date --date="UTC 1970-01-01 $beg secs" --iso-8601=seconds ); beg=$(( $beg + $inc ))
  echo ${date_out%+*}
 done
}

It generates the expected values for this command line example: gen_epoch 2014-04-01T00:00:00 2014-04-01T07:00:00 3600

expected values:

2014-04-01T00:00:00
2014-04-01T01:00:00
2014-04-01T02:00:00
2014-04-01T03:00:00
2014-04-01T04:00:00
2014-04-01T05:00:00
2014-04-01T06:00:00
2014-04-01T07:00:00

However i have tried this function on a server where i have no root privileges and i have found the following results:

2014-03-31T17:00:00
2014-03-31T18:00:00
2014-03-31T19:00:00
2014-03-31T20:00:00
2014-03-31T21:00:00
2014-03-31T22:00:00
2014-03-31T23:00:00
2014-04-01T00:00:00

and i have seen that the server time origin is not at 1970-01-01T00:00:00. typing TZ=UTC date --date="1970-01-01T00:00:00" +%s command gives the value of -25200 which corresponds to a 7 hours lag while it should give 0. My question is how this problem could be corrected on the server? Could You help me to find an equivalent solution for this function assuming that i don't know on which machine i am running it, so i have know apriori knowledge if the system time is correct or not?

Answer 1

Not a complete answer but too long for a comment.

I guess that this particular server is incorrectly configured upon setup. The problem is that BIOS clocks are set to localtime time, while the systems thinks it's in UTC (or vise versa) (use hwclock to query hardware clocks settings).

If the system is configured incorrectly and you can't fix it for any reason (don't have superuser account or whatever), I'd suggest to provide a "fixing timezone description file with your software and specify it in TZ variable like this: TZ=:/path/to/fixing/timezone date --date="1970-01-01T00:00:00" +%s. Obviously you have to pre-calculate which TZ description file fixes the problem and use a proper one. Usually available timezones are stored in /usr/share/zoneinfo