During a VM backup, the following error message appears in the backup log after it aborts a running backup task:

101: INFO: status: 1% (129309081/4294967296), sparse 0% (886784), duration 91, 33/33 MB/s 
[...] 
107: INFO: status: 80% (2706263244/4294967296), sparse 16% (698703462), duration 1950, 5/4 MB/s 
107: ERROR: interrupted by signal 
107: INFO: aborting backup job 

This error usually occurs when there is a version mismatch for the pve-qemu-kvm package in Proxmox. At the time of writing, the available pve-qemu-kvm package version is 2.9.0-4. Check for the version that is installed when you get this error during a backup. If you're using an older version, then upgrade to the latest version using the following command to fix the issue.