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It appears this is caused by the SIL Engine plugin:
SIL Engine is attempting to copy a JSP to JIRA's app directory, and failing due to permissions.
SIL Engine is a "library plugin", a dependency of other CPrime plugins, which I had experimented with in the past (Power Custom Fields, I think). The problem with "library plugins" is that they hang around even after the last plugin that used them is uninstalled. Thus; SIL Engine on my system.SIL Engine is attempting to copy a JSP to JIRA's app directory, and failing due to permissions.
Digression: Permissions in your /opt/atlassian/
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jira directory
The attempted copy failed ('Permission Denied'), and rightly so. JIRA (and any webapp) should absolutely not be allowed to write to its own installation directory. Back in 2009 I had not learned this. I was a volunteer administrator of https://jira.apache.org, and left the app directory writable, which contributed to the server being hacked:
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