My Zotero did not update, showing a dialog that while there is an update available, I apparently lacked the permissions to update. First I tried to chmod the directory where I extracted Zotero to, and the Zotero binary, but that did not change the error message. It turns out there is another directory that needs to be changed:
sudo chmod 707 /usr/bin/zotero && sudo chmod -R 707 /opt/zotero
(in the terminal) and now everything works as it should.
Update 10 April 2019: see comments for a more appropriate handling of the permissions.
Didier Ruedin 
Thanks! It works for me as well :)
Thanks for confirming that this worked on your machine!
Apparently this may not be permanent, so if you get this error again, just run the above code again…
Funcionó, muchas gracias.
Permissions 707 is equivalent to Other:Read+Write+Execute, that is — anyone can delete files in the /opt/zotero directory. Generous or reckelss?
If you’re in generous but sane mind, then allow this only to your Group (770), or if this is a personal Ubuntu, just set the ownership on the /opt/zotero to your user account:
chmod -R youruser:youruser /opt/zotero
OR, better yet — create another group, say, zotero, add your username to that group and set the ownership of the /opt/zotero to the group, while setting the permission to Group:Read+Wrtie+Execute:
——-
## 1.Create a new group: for example, new GID=2001, check what’s existing in ‘cat /etc/group’
sudo groupadd -g GID zotero
## 2.Add your USERNAME to zotero group
sudo adduser USERNAME zotero
## 3. Set ownership and group permissions on zotero installation dir, e.g. /opt/zotero
sudo chown -R root:zotero /opt/zotero
sudo chmod -R g+w /opt/zotero
——-
Update zotero from zotero menu Help>Check for Updates…
Alternatively, your username is probably a member of sudo group, so just run the step 3. for group named “sudo”, that is user root:sudo
Thanks for checking in with these details! As the sole user of the machine, I was happy enough for this quick fix. You are right, though, as a general fix, this may be too generous.
Thank you! This has been irritating me for a while.
perfect, thank you so much !