CentOS 7 error restarting/starting a systemd service: :Unable to register authentication agent

Issue

When restarting/starting CentOS 7 the following error arises:

# service pure-ftpd start
Redirecting to /bin/systemctl start pure-ftpd.service

** (pkttyagent:478736): WARNING **: 18:16:34.777: Unable to register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject
Error registering authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject (polkit-error-quark, 0)

Environment

• CentOS 7

Solution

1. Identify a service showing  the error:

# groupadd -g 23 nohidproc
# usermod -a -G nohidproc polkitd
# mount -o remount,rw,hidepid=2,gid=nohidproc /proc
# systemctl restart polkit

** (pkttyagent:490038): WARNING **: 18:18:27.326: Unable to register authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject
Error registering authentication agent: GDBus.Error:org.freedesktop.PolicyKit1.Error.Failed: Cannot determine user of subject (polkit-error-quark, 0)
# echo "proc /proc proc defaults,hidepid=2,gid=nohidproc 0 0" >> /etc/fstab
# mount -a
# systemctl restart polkit

2. Start/restart the service that was showing the error.

# service pure-ftpd start
Redirecting to /bin/systemctl start pure-ftpd.service