rsync_with_lock.sh

#!/bin/bash

# A simple wrapper script to avoid starting an rsync process
# if one is currently running
#
# Shyam Saladi (saladi@caltech.edu)
#
# parts from 
# https://superuser.com/a/848123/470760
#
# set up in crontab (as follows polls ever 5 minutes; should roughly be size_of_file / bandwidth / 2)
# crontab -e
# */5 * * * * bash SCRIPT_DIR/rsync_with_lock.sh FROM_DIRECTORY TO_DIRECTORY >> /tmp/rsync_with_copy.txt 2>&1

LOCK_NAME="rsync_files"
LOCK_DIR='/tmp/'${LOCK_NAME}.lock
PID_FILE=${LOCK_DIR}'/'${LOCK_NAME}'.pid'

if mkdir ${LOCK_DIR} 2>/dev/null; then
  # If the ${LOCK_DIR} doesn't exist, then start working & store the ${PID_FILE}
  echo $$ > ${PID_FILE}

  rsync --inplace $1 $2

  rm -rf ${LOCK_DIR}
  exit
else
  if [ -f ${PID_FILE} ] && kill -0 $(cat ${PID_FILE}) 2>/dev/null; then
    # Confirm that the process file exists & a process
    # with that PID is truly running.
    echo "Running [PID "$(cat ${PID_FILE})"]" >&2
    exit
  else
    # If the process is not running, yet there is a PID file--like in the case
    # of a crash or sudden reboot--then get rid of the ${LOCK_DIR}
    rm -rf ${LOCK_DIR}
    exit
  fi
fi