Manual upgrade

ssh chat.civicrm.org
sudo to root
cd /opt
cp -ra mattermost mattermost-$(date +'%F-%H-%M')
wget [latest mattermost version]
tar -x --transform='s,^[^/]\+,\0-upgrade,' -f mattermost*.gz
chown -hR mattermost:mattermost /opt/mattermost-upgrade/
find mattermost/ -mindepth 1 -maxdepth 1 \! $ -type d \( -path mattermost/config -o -path mattermost/logs -o -path mattermost/plugins -o -path mattermost/data $ -prune \) | xargs rm -r
cp -an /opt/mattermost-upgrade/. mattermost/
rm -rf /opt/mattermost-upgrade/

When ready, restart mattmost:

systemctl restart mattermost

Note that mattermost runs DB upgrades on restart, so do not interrupt the restart.

mattermost upgrades