Set FSCKFIX=yes in /etc/default/rcS


From the man page - man5/rcS.5.html
rcS - variables that affect the behavior of boot scripts
FSCKFIX
When the root and all other file systems are checked, fsck is invoked with the -a
option which means "autorepair". If there are major inconsistencies then the fsck
process will bail out. The system will print a message asking the administrator to
repair the file system manually and will present a root shell prompt (actually a
sulogin prompt) on the console. Setting this option to yes causes the fsck
commands to be run with the -y option instead of the -a option. This will tell
fsck always to repair the file systems without asking for permission.

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