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copied!<p>For shell scripts, I tend to go with the <code>mkdir</code> over <code>flock</code> as it makes the locks more portable.</p> <p>Either way, using <code>set -e</code> isn't enough. That only exits the script if any command fails. Your locks will still be left behind.</p> <p>For proper lock cleanup, you really should set your traps to something like this psuedo code (lifted, simplified and untested but from actively used scripts) :</p> <pre><code>#======================================================================= # Predefined Global Variables #======================================================================= TMPDIR=/tmp/myapp [[ ! -d $TMP_DIR ]] \ && mkdir -p $TMP_DIR \ && chmod 700 $TMPDIR LOCK_DIR=$TMP_DIR/lock #======================================================================= # Functions #======================================================================= function mklock { __lockdir="$LOCK_DIR/$(date +%s.%N).$$" # Private Global. Use Epoch.Nano.PID # If it can create $LOCK_DIR then no other instance is running if $(mkdir $LOCK_DIR) then mkdir $__lockdir # create this instance's specific lock in queue LOCK_EXISTS=true # Global else echo "FATAL: Lock already exists. Another copy is running or manually lock clean up required." exit 1001 # Or work out some sleep_while_execution_lock elsewhere fi } function rmlock { [[ ! -d $__lockdir ]] \ && echo "WARNING: Lock is missing. $__lockdir does not exist" \ || rmdir $__lockdir } #----------------------------------------------------------------------- # Private Signal Traps Functions {{{2 # # DANGER: SIGKILL cannot be trapped. So, try not to `kill -9 PID` or # there will be *NO CLEAN UP*. You'll have to manually remove # any locks in place. #----------------------------------------------------------------------- function __sig_exit { # Place your clean up logic here # Remove the LOCK [[ -n $LOCK_EXISTS ]] && rmlock } function __sig_int { echo "WARNING: SIGINT caught" exit 1002 } function __sig_quit { echo "SIGQUIT caught" exit 1003 } function __sig_term { echo "WARNING: SIGTERM caught" exit 1015 } #======================================================================= # Main #======================================================================= # Set TRAPs trap __sig_exit EXIT # SIGEXIT trap __sig_int INT # SIGINT trap __sig_quit QUIT # SIGQUIT trap __sig_term TERM # SIGTERM mklock # CODE exit # No need for cleanup code here being in the __sig_exit trap function </code></pre> <p>Here's what will happen. All traps will produce an exit so the function <code>__sig_exit</code> will always happen (barring a SIGKILL) which cleans up your locks.</p> <p>Note: my exit values are not low values. Why? Various batch processing systems make or have expectations of the numbers 0 through 31. Setting them to something else, I can have my scripts and batch streams react accordingly to the previous batch job or script.</p>

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