[ProgClub programming] top: st : time stolen from this vm by the hypervisor

Jevan Pipitone discussion-email-lists at jevan.com.au
Thu Jun 6 15:10:01 AEST 2019

I notice your lock is a folder (directory) which either exists or is 

A lock could alternatively be a blank (0 byte) file, like what you are 
doing for your "alarm".


Would the following code work for lock?:

unlock() {
   rm $ephemeralDataDir/lock
touch $ephemeralDataDir/lock || exit 1;
trap unlock EXIT



Original Code:

unlock() {
   rmdir $ephemeralDataDir/lock
mkdir $ephemeralDataDir/lock || exit 1;
trap unlock EXIT

I don't know whether there are any benefits of using a folder or using a 
0 byte file, for a lock status?


On Thu. 06-Jun.-19 7:20 am, John Elliot V | ProgClub wrote:
> On 5/6/19 12:23 pm, Roland Turner via programming wrote:
>> Assuming that you're not ready to embrace systemd (which, despite the
>> absurd documentation, is actually pretty simple for common cases):
>>      #! /bin/bash -e
>>      ...
>>      persistentDataDir=/var/lib/something
>>      alarm() {
>>       touch $persistentDataDir/alarm
>>      }
>>      trap alarm ERR
>>      [ -f $persistentDataDir/alarm ] && exit 1
>>> 4. I want to make sure only one copy of my process runs at a time
>> Under the same assumption:
>>      #! /bin/bash -e
>>      ...
>>      ephemeralDataDir=/var/run/something
>>      unlock() {
>>       rmdir $ephemeralDataDir/lock
>>      }
>>      trap unlock EXIT
>>      mkdir $ephemeralDataDir/lock
> Thanks for those examples, very handy! I've written them up for John's
> Linux Page:
> https://www.progclub.org/wiki/John%27s_Linux_page#Stopping_a_script_from_running_if_it_previously_exited_due_to_error
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