@Seedy There could be various reasons. You have to see the full agent logs. However to start with this issue I would suggest few sanity checks.
1)Resolve network issue related to firewall restrictions in accessing the repo files
2)Correct permissions on /opt/cloudera/ directories
3)Check and change the ownership.
$chown cloudera-scm:cloudera-scm /opt/cloudera/parcel-repo/*
4)Re - add the hosts from Cloudera Manager
However most importantly you have to see if you can download the parcels manually on the node under this dir. Please follow the below page for detailed overview.
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