Bitcoin Node in error Deserialize/Failed to read undo block data

[jfpoub]

Hi,

Could you please help me to resolv this problem with bitcoin node

2026-01-02T17:40:18Z [error] Deserialize or I/O error - ReadVarInt(): size too large: iostream error at FlatFilePos(nFile=5101, nPos=15996136) while reading block undo
2026-01-02T17:40:18Z [error] A fatal internal error occurred, see debug.log for details: Failed to read undo block data 00000000000000000000d709037a9623724d9fccb4de2001b26860651d6768d7 from disk
Error: A fatal internal error occurred, see debug.log for details: Failed to read undo block data 00000000000000000000d709037a9623724d9fccb4de2001b26860651d6768d7 from disk

I explored some topic and did

sudo umount /dev/sda3

=> target is busy

sudo lsof /dev/sda3 gives a lot of lines although bitcoin node is stopped and electrs and bitaxe sentry and public pool and mempool and tailscale.

I can not kill all residual processes handly !

How to repare /dev/sda3, that i tought it is bad , in an umbrel mode permitting the repare process ?

or to repare the bitcoin node with option chainstate ?

[jfpoub]

I thought that /dev/sda3 was corrupted due to

Free Blocks count wrong

Free inodes count wrong

But is is a false problem (I recreated a new VM UmbrelOS and i had the same warnings)

If you suspect a corrupt, the only way to check filesystem (during boot) is to :

modify /etc/fstab

sudo nano /etc/fstab

modify line / and at the end of line 1 0 to 1 1

modify line /data and at the end of line the 0 0 to 0 2

CTRL-O to write on disk the changes

ENTER

CRTL-X to exit

cat /etc/fstab to verify the changes

[jfpoub]

To correct the bitcoin node :

stop the bitcoin node

sudo nano /home/umbrel/umbrel/app-data/bitcoin/data/bitcoin/bitcoin.conf

add the line

reindex-chainstate=1

CTRL-O ENTER CTRL-X

to write and exit

cat /home/umbrel/umbrel/app-data/bitcoin/data/bitcoin/bitcoin.conf

to verify

restart bitcoin node

Next time (after the reindexing is finished) , comment with a # the line reindex-chainstate=1 to deactivate it.