#if u have the root password which default is "alpine"
1.login as root, using command "ssh root@ip address"
2.type ur password: alpine
3.type command "passwd" to change ur root password
4.when it is done, type command "passwd mobile" to change the mobile passwd

#if u forget ur root passwd
1.open the file named "master.password" at /private/etc on ur ios jailbreak ios device
2.find the string like this:
root:xxxxxxxxxxxxx:0:0::0:0:System Administrator:/var/root:/bin/sh
mobile:xxxxxxxxxxxxx:501:501::0:0:Mobile User:/var/mobile:/bin/sh
3.change the string "xxxxxxxxxxxxx" to "/smx7MYTQIi2M" and ur root or mobile password is reset to "alpine"