Systemd Path Monitor Folder

Description:

So I needed an event based way to monitor /csv for specific csv file patterns. For this example, the pattern the application writes is dataset_1.csv where the number increments on the end. Here is how I set RHEL 7 to run a script every time a file was written matching /csv/dataset_*.csv:

To Resolve:

1. Run:

   • vi /usr/local/bin/csv.ps1

   • Paste/save:

   #!/usr/bin/env pwsh
   $date = Get-Date -Format "yyyy-MM-dd-HH:mm:ss"
   write-output "$date : new file" > /home/myuser/new-file.txt
   

   • Now test run

   chmod +x /usr/local/bin/csv.ps1
   ./csv.ps1
   cat /home/myuser/new-file.txt
   # 2020-06-05-12:00:49 : new file
   

2. Configure a new service and have it run that script when a pattern is found:

   cd /etc/systemd/system
   touch monitorcsv.service
   vi monitorcsv.service
   
      [Unit]
      Description="Monitor csv directory"
   
      [Service]
      ExecStart=/usr/local/bin/csv.ps1
   
   touch monitorcsv.path
   vi monitorcsv.path
   
      [Unit]
      Description="Monitor the /csv for changes"
   
      [Path]
      PathExistsGlob=/csv/dataset*.csv
      Unit=monitorcsv.service
   
      [Install]
      WantedBy=multi-user.target
   
   systemd-analyze verify /etc/systemd/system/monitorcsv.*
   # gave errors for other services but not the one I created? Moving on...
   
   sudo systemctl start monitorcsv.path
      
   # Now, we see if it is working...
   rm /home/myuser/new-file.txt
   ll /csv/
   # no dataset*.csv files
   touch /csv/dataset_12.csv
   cat /home/myuser/new-file.txt
   # 2020-06-05-12:12:20 : new file
   # Sweet! Lets see if it fires if we move the csv - it doesn't write
   
   
   cat /home/myuser/new-file.txt
   2020-06-05-12:17:25 : new file
   mv /csv/dataset_12.csv /csv/processed/dataset_12.csv
   cat /home/myuser/new-file.txt
   2020-06-05-12:17:25 : new file
   # exactly what we wanted, it doesn't fire because we moved a file from that directory to another
   

3. Post config

   # run on startup
   systemctl enable monitorcsv.path
   
   # troubleshooting (if needed)
   systemctl status monitorcsv.path
   journalctl -u monitorcsv.path
   

References:

“Systemd Path Units”