How does Linux verify the login password?

Question

I would like to know how the password verification in Linux works.

I know that the passwords are stored as a hash in /etc/shadow file and user information is in /etc/passwd file. My understanding is this:

Selecting what user you want to login as decides what user name the system should check.
When you enter the password and hit enter, the system goes to the /etc/shadow file and finds the line corresponding to the user name.
From step 2 it gets the hash of the actual password. It then generates the hash of the entered password and compares both of them. If a match is found, voilà. Else, error message.

Is my understanding correct?

Linux in a kernel found on many very different operating systems, it doesn't deal with user passwords. Please specify the Linux-based operating system you're talking about (Debian, Android, ChromeOS, Fedora, OpenWRT...). Only some systems (and only in some deployments) use /etc/passwd,shadow to store user information — Stéphane Chazelas
– Stéphane Chazelas, Commented Aug 5, 2014 at 16:33

Willian Paixao · Accepted Answer · 2017-10-20 08:54:48Z

6

Yes. You're correct. Each steps can be split in minor tasks as well, but you describe the overall algorithm.

Follow a couple of articles describing in details the login process. [1] [2]

Note that this is only about the plain password, not mentioning PAM system. [3]

answered Aug 5, 2014 at 15:33

Willian Paixao

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