/usr/sbin/tar-backup is in tar-scripts 1.29b-2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
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# Make backups.
# Copyright 2004-2006, 2013 Free Software Foundation
# This file is part of GNU tar.
# GNU tar is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
# GNU tar is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
# Load library routines
SYSCONFDIR=${SYSCONFDIR-/usr/etc}
. ${LIBDIR-/usr/lib/tar}/backup.sh
DUMP_LEVEL=0
TIME=
NOW=`now`
usage() {
    	cat - <<EOF
usage: $PROGNAME [OPTIONS] [WHEN]
Options are:
   -l, --level=LEVEL       Do backup level LEVEL (default $DUMP_LEVEL).
   -f, --force             Force backup even if today's log file already
                           exists.
   -v, --verbose[=LEVEL]   Set verbosity level. Default 100.
   -t, --time=TIME         Wait till TIME, then do backup.
Informational options:
   -h, --help              Display this help message.
   -V, --version           Display program version.
   Optional argument WHEN is for backward compatibility only. It has been
   superseded by --time option.
   TIME argument can be one of:
	now          --     do backup immediately.
	HH           --     do backup at HH hours.
	HH:MM        --     do backup at HH:MM.
Send bug reports to bug-tar@gnu.org.
EOF
}
# For compatibility with previous versions, deduce the backup level
# from the command name
case "$PROGNAME" in
level-[0-9]) DUMP_LEVEL=`expr $PROGNAME : 'level-\([0-9][0-9]*\)'`;;
esac
for opt
do
  if [ -z "$prev" ]; then
      option=$opt
      optarg=`expr "x$opt" : 'x[^=]*=\(.*\)'`
  else
      option="${prev}=$opt"
      prev=""
      optarg=$opt
  fi
  case $option in
  --l=*|--le=*|--lev=*|--leve=*|--level=*)
         DUMP_LEVEL=$optarg
	 ;;
  -l?*)  DUMP_LEVEL=`expr $option : '-l\(.*\)'`;;
  -l|--l|--le|--lev|--leve|--level)
	 prev=--level
	 ;;
  --verb=*|--verbo=*|--verbos=*|--verbose=*)
         VERBOSE=$optarg
	 ;;
  -v|--verb|--verbo|--verbos|--verbose)
         VERBOSE=100
	 ;;
  -v*)   VERBOSE=`expr $option : '-v\(.*\)'`;;
  --t=*|--ti=*|--tim=*|--time=*)
         TIME=$optarg
	 ;;
  -t?*)  TIME=`expr $option : '-t\(.*\)'`;;
  -t|--t|--ti|--tim|--time)
	 prev=--time
    	 ;;
  -V|--v|--ve|--ver|--vers|--versi|--versio|--version)
    	 echo "backup (GNU tar) 1.29"
	 license
	 exit;;
  -h|--h|--he|--hel|--help)
	 usage
	 exit;;
  -f|--f|--fo|--for|--forc|--force)
      	 FORCE=yes
	 ;;
  *)     if [ "x$TIME" != "x" ]; then
            bailout "Extra argument. Try $PROGNAME --help for more info."
         else
            TIME=$option
         fi;;
  esac
done
if [ "x$TIME" = x ]; then
    bailout "No backup time specified. Try $PROGNAME --help for more info."
    exit 1
fi
init_backup
# Maybe sleep until around specified or default hour.
wait_time $TIME
if [ $DUMP_LEVEL -ne 0 ]; then
    PREV_LEVEL=`expr $DUMP_LEVEL - 1`
    PREV_DATE=`ls -t ${LOGPATH}/log-*-level-$PREV_LEVEL|
                head -n 1|
		sed "s,${LOGPATH}/log-\(.*\)-level.*,\1,"`
    if [ "x$PREV_DATE" = x ]; then
        bailout "Can't determine date of the previous backup"
    fi
    message 0 "Backup from $PREV_DATE to $NOW"
fi
# start doing things
# Make sure the log file did not already exist.  Create it.
if [ "x$FORCE" = "xyes" ]; then
    rm ${LOGFILE}
fi
if [ -f "${LOGFILE}" ] ; then
   bailout "Log file ${LOGFILE} already exists."
else
   touch "${LOGFILE}"
fi
message 1 "Ready for backup."
message 10 "TAR invocation: $TAR_PART1"
message 20 "Variables:"
message 20 "BACKUP_DIRS=$BACKUP_DIRS"
message 20 "BACKUP_FILES=$BACKUP_FILES"
# The buch of commands below is run in a subshell for which all output is
# piped through 'tee' to the logfile.  Doing this, instead of having
# multiple pipelines all over the place, is cleaner and allows access to
# the exit value from various commands more easily.
(
 message 1 "preparing tapes"
 $MT_BEGIN "${TAPE_FILE}"
 rm -f "${VOLNO_FILE}"
 message 1 "processing backup directories"
 set - ${BACKUP_DIRS}
 while [ $# -ne 0 ] ; do
     date="`date`"
     fs="`echo \"${1}\" | sed -e 's/^.*://'`"
     fs=`root_fs $fs`
     fsname="`echo \"${1}\" | sed -e 's/\//:/g'`"
     remotehost="`expr \"${1}\" : '\([^/][^/]*\):.*'`"
     if [ -z "$remotehost" ]; then
	 remotehost=$localhost
     fi
     echo "Backing up ${1} at ${date}"
     message 10 "fs=$fs"
     message 10 "fsname=$fsname"
     message 10 "remotehost=$remotehost"
     if [ $DUMP_LEVEL -eq 0 ]; then
	 make_level_log ${remotehost}
     else
	 echo "Last `prev_level` dump on this filesystem was on $PREV_DATE"
	 remote_run "${remotehost}" cp "`level_log_name ${fsname} $PREV_LEVEL`" "`level_log_name temp`"
     fi
     ${DUMP_BEGIN-:} $DUMP_LEVEL $remotehost $fs $fsname
     backup_host ${remotehost} \
                "--listed=`level_log_name temp`" \
                "--label='`print_level` backup of ${fs} on ${remotehost} at ${NOW}'" \
		-C ${fs} .
     # 'rsh' doesn't exit with the exit status of the remote command.  What
     # stupid lossage.  TODO: think of a reliable workaround.
     if [ $? -ne 0 ] ; then
	 echo "Backup of ${1} failed." 1>&2
         # I'm assuming that the tar will have written an empty
         # file to the tape, otherwise I should do a cat here.
     else
         flush_level_log ${remotehost} ${fsname}
     fi
     ${MT_STATUS} "$TAPE_FILE"
     ${DUMP_END-:} $DUMP_LEVEL $remotehost $fs $fsname
     echo "sleeping ${SLEEP_TIME} seconds"
     sleep ${SLEEP_TIME}
     shift
 done
 # Dump any individual files requested.
 if [ "x${BACKUP_FILES}" != "x" ] ; then
     message 1 "processing individual files"
     date="`date`"
     if [ $DUMP_LEVEL -eq 0 ]; then
         make_level_log $localhost
     else
	 echo "Last `prev_level` dump on this filesystem was on $PREV_DATE"
	 remote_run "${localhost}" cp "`level_log_name MISC $PREV_LEVEL`" "`level_log_name temp`"
     fi
     echo "Backing up miscellaneous files at ${date}"
     ${DUMP_BEGIN-:} $DUMP_LEVEL $localhost MISC MISC
     backup_host $localhost \
               "--listed=`level_log_name temp`"\
               "--label='`print_level` backup of miscellaneous files at ${NOW}'" \
               ${BACKUP_FILES}
     if [ $? -ne 0 ] ; then
	 echo "Backup of miscellaneous files failed."
	 # I'm assuming that the tar will have written an empty
	 # file to the tape, otherwise I should do a cat here.
     else
	 flush_level_log $localhost MISC
     fi
     ${MT_STATUS} "$TAPE_FILE"
     ${DUMP_END-:} $DUMP_LEVEL $localhost MISC MISC
 else
     echo "No miscellaneous files specified"
 fi
 message 1 "final cleanup"
 $MT_REWIND "${TAPE_FILE}"
 $MT_OFFLINE "${TAPE_FILE}"
 echo "."
) 2>&1 | tee -a "${LOGFILE}"
if test "${ADMINISTRATOR}" != NONE; then
     echo "Sending the dump log to ${ADMINISTRATOR}"
     mail -s "Results of backup started ${startdate}" ${ADMINISTRATOR} < "${LOGFILE}"
fi
# EOF
 |