Why geth switch to full node when starting

Question

I start my geth with --syncmode "fast" but I get this warning:

WARN [01-21|14:47:59.148] Switch sync mode from fast sync to full sync

And my geth will start with full sync mode with this warning. Any solution for this?

OS version: CentOS Linux 7

Full command:

$ go-ethereum/build/bin/geth --syncmode "fast" --rpc --rpcapi db,eth,net,web3 --cache=16384 --rpcport 8545 --rpcaddr 0.0.0.0

Is your node already synced, or close to synced?
– Raghav Sood
Commented Jan 21, 2020 at 6:56 — Raghav Sood, Commented Jan 21, 2020 at 6:56
Still syncing, block number 9299098 now
– superrman777
Commented Jan 21, 2020 at 6:59 — superrman777, Commented Jan 21, 2020 at 6:59

Raghav Sood · Accepted Answer · 2020-01-21 07:03:09Z

4

A fast sync will switch to a full sync mode as it reaches the chain tip, once enough of the state trie has been synced in fast mode.

Going forward from that time, it will sync in full mode and download and evaluate each block vs. pulling just the state trie changes as in fast mode.

Your node is quite close to the chain tip, and has likely passed the point for which it was aiming in its fast sync - it is expected behaviour.

answered Jan 21, 2020 at 7:03

Raghav Sood

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1

Thanks for you answer. One more question here, can I run light mode from 0 block then switch to full mode when my node is close to the chain tip ?
– superrman777
Commented Jan 21, 2020 at 7:23
2

If you run as a light node, you won't have the information to run a full node - if you switch to a full node, it will start syncing from scratch (or from the last full block you have, in case you previously ran a fast or full sync completely at some point before switching to the light mode)
– Raghav Sood
Commented Jan 21, 2020 at 7:29
1

I'm 10 months behind, how can I get it to stay on fast sync?
– CQM
Commented Jan 9, 2021 at 4:31
1

Did you try --syncmode fast ?
– Himmet Avsar
Commented Apr 14, 2021 at 0:17
1

question remains why this is logged as warning rather then info.
– omni
Commented Apr 26, 2021 at 8:24

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