Minecraft – How to enable command blocks on the Minecraft realm

You can use them as you would use a regular command in chat.

Example:

• /give [user] 1 2

This gives [user] two of item id 1 when the command block is activated with redstone.

• /gamemode [user] [0, 1, 2]

This will change [user]'s gamemode to either 0 (Survival) 1 (Creative) or 2 (Adventure)

Note and Edit: Buttons S (Survival) C (Creative) and A (Adventure) work as well as SevenSidedDie has noted for /gamemode

The syntax for the sudo command is /<command> <player> <command [args]> and its description is Make another user perform a command. With the command /sudo @a gc you force every player to execute /gc. Means everyone see the server usage information.

If you typed /sudo @a save-all in the commandblock, be happy that it dosen't work because that could be ending in a server crash. (Everybody on the server is forced to execute the command /save-all, what needs much hardware usage)

What I think that you missleading it with the sudo command from linux where the command is executed as root.

The problem why you can not execute the command /save-all in a commandblock is because it is disabled from the server itself for security reasons.

In the Minecraft Wiki you find that information:

These commands are likely disabled due to limited use in command blocks and the potential for severe, unintended consequences on servers.

That counts for the commands:

ban, ban-ip, deop, kick, op, pardon, pardon-ip, save-all, save-off, save-on, stop, whitelist add/remove/on/off/reload, debug, publish

If you really need that command, the only possibility is to use a command of a other plugin and not the original command /save-all.

But make sure that it is executed only once! Keep in mind that griefer could use it to crash the server by expensive hardware usage if they spam the button!