UNIX for Dummies Questions & Answers

can somebody tell me what exactly fsck command does ?
please dont post the man page for it I already read it

fsck means "filesystem check".

Verifies a filesystem is in order. A bit like chkdsk on Microsoft.

@hicksd8 you are right i knew that but due to improper shutdown file system of my machine became read only i ran fsck and it worked. So my question is what fsck does and how it converted fs of my system to write mode as well ?

Right, I understand your question.

When the system shuts down properly, filesystems are dismounted in an orderly fashion and that is recorded on the filesystem. Therefore, if a filesystem is not properly dismounted (eg, a crash) the system can see that when it boots. It therefore requests a clean-up (or in some systems it will do a clean-up automatically) thereby ensuring that the filesystem is in order.

If filesystems are very corrupt, an automated fsck can "destroy the filesystem on the ground" leaving a full recovery as the only option. Therefore, many systems go into read-only to allow we sysadmins to look at things in a more cautious manner.

When the system knows that the integrity of the filesystem(s) is good, it is happy to mount and go.