Instead of caveat, refer to flock(1)

[hoxu]

Instead of contemplating reimplementing locking in btrfs-backup, you could just tell people to use flock(1) utility for locking. flock -n is perfect for this usecase :)

[hale]

Like this?

#!/bin/sh
flock -n /tmp/btrfs-backup.lockfile -c ionice -c 3 /location/of/btrfs-backup.py /source /destination

[hoxu]

With -c you need to quote the command flock passes to shell. I personally just use it without the -c parameter:

flock -n /tmp/foo.lockfile command param1 param2 etc

Perfect for potentially long-running jobs like backups :)

[lordsutch]

Added instructions to README.md. Thanks!

[hale]

Thank you :)