passwd: Only root can specify a user name.

Below you can see its showing as only root can change .what does that mean ?

Yes That mean only root can only change the password .

Then how  can non-root user can change the password ?

non-user also can change the password with the command #passwd   (without specifying a user name ).

It will prompt for current passwd . then new passwd , retype new passwd again .

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how to change user password without current password ?