rm -r /var/cache/app-info

rm: descend into write-protected directory '/var/cache/app-info'? y 
rm: descend into write-protected directory '/var/cache/app-info/xapian'? y
rm: descend into write-protected directory '/var/cache/app-info/xapian/default'? y
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/postlist.baseB'? y
rm: cannot remove '/var/cache/app-info/xapian/default/postlist.baseB': Permission denied
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/termlist.DB'? y
rm: cannot remove '/var/cache/app-info/xapian/default/termlist.DB': Permission denied
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/postlist.baseA'? y
rm: cannot remove '/var/cache/app-info/xapian/default/postlist.baseA': Permission denied
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/spelling.baseA'? y
rm: cannot remove '/var/cache/app-info/xapian/default/spelling.baseA': Permission denied
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/record.baseB'? y
rm: cannot remove '/var/cache/app-info/xapian/default/record.baseB': Permission denied
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/record.baseA'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/termlist.baseB'? 
rm: remove write-protected regular empty file '/var/cache/app-info/xapian/default/flintlock'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/spelling.DB'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/termlist.baseA'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/spelling.baseB'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/iamchert'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/record.DB'? 
rm: remove write-protected regular file '/var/cache/app-info/xapian/default/postlist.DB'? 
rm: descend into write-protected directory '/var/cache/app-info/xmls'? 
rm: descend into write-protected directory '/var/cache/app-info/yaml'? 

-------------------------------------------------------------

~$ sudo appstreamcli refresh --force --verbose

** (appstreamcli:4541): DEBUG: Refreshing AppStream cache
** (appstreamcli:4541): DEBUG: Reading: /usr/share/app-info/xmls/org.freedesktop.fwupd.xml
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial_universe_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial-updates_main_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial-updates_restricted_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/security.ubuntu.com_ubuntu_dists_xenial-security_restricted_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/security.ubuntu.com_ubuntu_dists_xenial-security_multiverse_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/security.ubuntu.com_ubuntu_dists_xenial-security_main_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/security.ubuntu.com_ubuntu_dists_xenial-security_universe_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial_main_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial_restricted_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/lib/app-info/yaml/gb.archive.ubuntu.com_ubuntu_dists_xenial_multiverse_dep11_Components-amd64.yml.gz
** (appstreamcli:4541): DEBUG: Reading: /var/cache/app-info/xmls/fwupd.xml
** (appstreamcli:4541): DEBUG: Reading: /var/cache/app-info/yaml/xenial-main_amd64.yml.gz
** (appstreamcli:4541): DEBUG: Detected colliding ids: plan.desktop was already added with the same priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: flcheckers.desktop was already added with the same priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: flblocks.desktop was already added with the same priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: flsudoku.desktop was already added with the same priority.
** (appstreamcli:4541): DEBUG: Replaced 'firefox.desktop' with data of higher priority.
** (appstreamcli:4541): DEBUG: Replaced 'thunderbird.desktop' with data of higher priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: thunderbird.desktop was already added with a higher priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: org.gnome.Software.desktop was already added with a higher priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: firefox.desktop was already added with a higher priority.
** (appstreamcli:4541): DEBUG: Detected colliding ids: language-selector.desktop was already added with a higher priority.
** (appstreamcli:4541): DEBUG: zathura-pdf-poppler.desktop extends zathura.desktop, but zathura.desktop was not found.
** (appstreamcli:4541): DEBUG: WARNING: Skipped component 'com.steelseries.rival-legacy.firmware': The component is invalid.
** (appstreamcli:4541): DEBUG: Removing old rebuild-dir from previous database rebuild.
AppStream cache update completed, but some metadata was ignored due to errors.