Is you phone rooted? If it's not then there's no chance of that command working.

Even if it is most stock ROMs don't support that command, though if you are rooted you could try "adb shell" followed by "su" to allow you to execute commands over adb with superuser privileges.

 

Well I'm afraid that gaining root access to an unrooted device is not as simple as just typing "adb root". That command is to give the adb daemon root access (so you can issue ADB commands with root privileges), and so can only be used if you already have the ability to give apps root privileges, i.e. if the device is already rooted. It isn't something that can be used to root a phone. And as I said, it doesn't work on most phones even if they are rooted.

Rooting techniques are usually specific to the device, so I can't tell you how to root this particular phone. The closest thing there is to a generic approach is to unlock the bootloader, flash a custom recovery using fastboot, and use the custom recovery to install the superuser package. But that depends on there being a way to unlock the bootloader (depends on the phone and on whether it's a carrier-branded model or not, and if it is on which carrier) and on whether a custom recovery exists for that particular model (they have to be built for the particular model: you can properly brick the phone using one that was written for a different model). Some phones have other ways of doing it, but as I say those depend on the phone and I don't know this device. Phones with older Android versions can often be rooted by "one click" type apps, but the exploits those used have mostly been closed now so they generally don't work on newer versions (and this is a good thing, partly because some of those apps inserted stuff you'd rather not have as well, but mainly because the same security holes that they used could also be used by malware to get far deeper into the phone than it possibly could otherwise).

 

That thread is 5 years old. The method doesn't work on newer phones.