What are the default passwords of the user and root in the docker container?

[songkq]

When I try to modify the password through echo "user:pass" | chpasswd , it raised errors as the followings,

Changing password for user.
unix_chkpwd[2275]: password check failed for user (user)
chpasswd: (user user) pam_chauthtok() failed, error:
Authentication token manipulation error
chpasswd: (line 1, user user) password not changed