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Use Ubuntu 16.04 LTS, what happened was the following. All the connections stopped working from one moment to another, I had a fault in the internet, the networks fell but when the internet came back, the connection did not work again either wired or wireless, neither by bluetooth nor by usb, and gives that error when I frame journalctl -xe :

kernel: audit: type=1400 audit(1549657329.185:141): apparmor="DENIED" operation="open" profile="/usr/lib/NetworkManager/nm-dhcp-helper" name="/usr/lo"
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2 Answers 2

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One problem that could be blocking is the path where the rule is pointing out.

My error message was complaining about name=/var/run/NetworkManager/private-dhcp and the rule was /run/NetworkManager/private-dhcp rw,

I've solved this problem adding and alias in /etc/apparmor.d/tunables/alias

alias /run/ -> /var/run/,

then rebooted the apparmor :

service apparmor reload
service networking reload
service network-manager reload
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It seems an old bug in isc-dhcp package. AppArmor (a security software like SELinux) deny dhclient process to open /usr/lib/NetworkManager/nm-dhcp-helper. As you can see from link this bug occurs on Ubuntu with specific version of Hardware Enablement (HWE) Linux Kernel Version.

You can try proposed solution, adding following lines to /etc/apparmor.d/sbin.dhclient

network inet dgram,
network inet6 dgram,

just after trace (readby) peer=/usr/sbin/NetworkManager,

then you need to:

apparmor_parser -r /etc/apparmor.d/sbin.dhclient
service apparmor restart
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  • What is a fix for this issue? I start to have in in 2021 just few days ago on random basis. Only one way tmp to fix it is to restart network service few times which is very annoying
    – Viktor
    Feb 2, 2021 at 20:42
  • You can try the proposed solution: add to sbin.dhclient the two lines "network inet dgram" and "network inet6 dgram" then restart apparmour.
    – balucio
    Apr 15, 2021 at 7:45
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    In file sbin.dhclient there is no trace (readby) but i have ptrace (readby)
    – Viktor
    Apr 19, 2021 at 16:27

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