hsm_secret is used to derive keys for both onchain and offchain (channels commitments) transactions.
To retrieve on chain funds you can rescan the block chain for your utxos by using the
--rescan startup option of
You can not re create the whole state of your channels just from the
hsm_secret, which are stored in the database. Moreover it's very discouraged to restore from a backed up database (penalty transactions...).
Fortunately, with the
option_static_remotekey now enabled by default you can now claim your funds onchain after your peer force closed the channel (if the channel was opened when both peers signaled this option).
The process is detailed here as part of the C-lightning FAQ draft.
How do i backup, in practice ?
The different backup solutions currently available are detailed here.