GLabels is a free software tool to generate labels/barcodes for various purposes. GLabels can be made use for label creation and print on label printing papers (e.g. Avery-6121, 65 per sheet)
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Install glabels
Either you can search and install
glabels from the Ubuntu Software Center.
sudo apt-get install glabels
You can find Glabels in Application > Office > Glabels
Prepare a list for barcode/label creation
Prepare a Report in Koha to get the list of the barcode (accession number) and call number.