upgrading to 19.07.8 will be my first upgrade. According to the luci sys upgrade, i have to deceide to uncheck or not the “Keep settings” checkbox.
If I understood correctly, not selecting this option implies to reconfigure everything and selecting this option may cause conflicts with the configuration files.
how can i be sure that it's safe to upgrade with the “Keep settings” checkbox checked ?
Keeping your settings while upgrading to a service release should be safe. For upgrading to a new major release it's recommended (although in most cases not strictly necessary) to start clean.
If "keep settings" didn't work you can always start from scratch plus you can compare the different config files e.g. /etc/config/unbound with the new one from the package with is named /etc/config/unbound-opkg
Additonally packages you installed always have to be installed again if you are not using some script or opkg feature.
Thank's. it's more tricky than expected. After the update, i can't perform an opkg update.
opkg update
Downloading http://downloads.openwrt.org/releases/19.07.8/targets/mvebu/cortexa9/packages/Packages.gz
Failed to send request: Operation not permitted
*** Failed to download the package list from http://downloads.openwrt.org/releases/19.07.8/targets/mvebu/cortexa9/packages/Packages.gz