Systemd Path Monitor Folder

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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:

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    #!/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
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    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:

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    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

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

References:

“Systemd Path Units”

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