If using a remote connection with virt-manager, and the remote host has 'zsh' as the default shell, virt-manager will fail to open a VNC session. Fixed upstream with these two small commits:
This request was evaluated by Red Hat Product Management for inclusion in a Red
Hat Enterprise Linux major release. Product Management has requested further
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Created attachment 414884 [details]
Straight backport from upstream
Fix built in virt-manager-0.8.4-3.el6
Verified PASSED with virt-manager-0.8.4-6.el6.
Red Hat Enterprise Linux 6.0 is now available and should resolve
the problem described in this bug report. This report is therefore being closed
with a resolution of CURRENTRELEASE. You may reopen this bug report if the
solution does not work for you.