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Problem:
You are trying to run iotop but you see an error message like
Netlink error: Operation not permitted (1) The Linux kernel interfaces that iotop relies on now require root priviliges or the NET_ADMIN capability. This change occured because a security issue (CVE-2011-2494) was found that allows leakage of sensitive data across user boundaries. If you require the ability to run iotop as a non-root user, please configure sudo to allow you to run iotop as root. Please do not file bugs on iotop about this.
Solution:
You need to run iotop as root:
sudo iotop
The reason for this is that iotop needs to access kernel interfaces that are only accessible to root users or if the user/process has the CAP_NET_ADMIN capability. In theory you could add this capability using sudo setcap cap_net_admin+ep /usr/sbin/iotop but on Ubuntu 18.04 this did not work for me.