Cannot start C-lightning after reboot I have problems starting up C-lightning's lightningd on Debian Buster under vagrant.
Steps I followed:

Fresh install bitcoind
Install lightningd
Run rpc commands - all good.
Reboot system
Get the error

Following is the output of lightnind after reboot:
2020-07-20T02:59:44.639Z UNUSUAL plugin-bcli: Could not connect to 'lightning-rpc': Connection refused
2020-07-20T02:59:44.652Z INFO plugin-bcli: bitcoin-cli initialized and connected to bitcoind.
2020-07-20T02:59:44.730Z UNUSUAL lightningd: Waiting for initial block download (this can take a while!)
2020-07-20T02:59:44.732Z UNUSUAL lightningd: Unable to estimate opening fees
...
2020-07-20T02:59:44.732Z UNUSUAL lightningd: Unable to estimate max_acceptable fees
2020-07-20T02:59:44.925Z UNUSUAL plugin-bcli: bitcoin-cli getblock 00000000000000ad6082acfe902b2ee294f4d1219f12b67bf59f88bb9d4af729 0 exited with status 1
The first line is normal behaviour:
UNUSUAL plugin-bcli: Could not connect to 'lightning-rpc': Connection refused


Your lightningd cannot start if the underlying bitcoind is not up-to-date:
2020-07-20T02:59:44.730Z UNUSUAL lightningd: Waiting for initial block download (this can take a while!)
2020-07-20T02:59:44.732Z UNUSUAL lightningd: Unable to estimate opening fees
...
2020-07-20T02:59:44.732Z UNUSUAL lightningd: Unable to estimate max_acceptable fees

You just need to wait for bitcoind to finish IBD. lightningd will regularly poll it and launch as soon as it's synced.