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What is journaling filesystem in linux.?

Hello,

A journaling filesystem is a filesystem that maintains a special file called a journal that is used to repair any inconsistencies that occur as the result of an improper shutdown of a computer. Such shutdowns are usually due to an interruption of the power supply or to a software problem that cannot be resolved without a rebooting.

A filesystem is a way of storing information on a computer that usually consists of a hierarchy of directories (also referred to as the directory tree) that is used to organize files. Each hard disk drive (HDD) or other storage device as well as each partition (i.e., logically independent section of a HDD) can have a different type of filesystem if desired.

Journaling filesystems write metadata (i.e., data about files and directories) into the journal that is flushed to the HDD before each command returns. In the event of a system crash, a given set of updates may have either been fully committed to the filesystem (i.e., written to the HDD), in which case there is no problem, or the updates will have been marked as not yet fully committed, in which case the system will read the journal, which can be rolled up to the most recent point of data consistency.