The connection to the Univention update servers and or the autoentication of packages or package lists may fail for a number of reasons.
Possible error messages you may encounter in the UMC, the App Center, commandline or updater.log:
WARNING: The following packages cannot be authenticated!
Error: Update aborted due to configuration error: Configuration error: non-existing component prefix
W: A error occurred during the signature verification.
W: Failed to fetch some URL Hash Sum mismatch
W: Failed to fetch some URL Sub-process /bin/bzip2 returned an error code (2)
In many cases these probems arise from proxy and/or firewall solutions that interfere in the HTTP traffic with the download servers.
As first step firewall and/or proxy solutions should be configured to whitelist (may be called “skipplist” as well) Univention Repository-Servers:
Depending on the installes applications, further servers should be whitelisted, like:
In addition, some firewall and/or proxy solutions may have problems with apt pipelining it’s HTTP requests (for users of Sophos UTM, please see the link in the “Additional Information” section below).
You may disable HTTP pipelinig for apt with the following command. This also tries to tell proxy server not to serve cached content:
cat /etc/apt/apt.conf.d/00broken-proxy __CONF__