If your filesystem is corrupted. That can be a hardware failure, or a software corruption (after a crash). The server won't boot before you manually run fsck to check/repair the filesystem. Note that this might not be possible if the problem is comming from hardware failure (hope you have backups....).
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Try this:
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- when you're prompted to, enter the root password, you'll be dropped on a shell
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- manually run fsck
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e2fsck -D -tt -y /dev/main/root
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It can take several minutes/hours depending on the size of your drives and their speed. With some luck, the filesystem will be cleaned, and you'll be able to boot.