can't adduser on unix

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http://serverfault.com – When I enter sudo adduser git i get sudo: useradd: command not found when I enter whereis adduser I get /usr/sbin/adduser but I can't switch to it root@431901-web1 [/usr/sbin]$ cd adduser bash: cd: adduser: Not a directory when I do a ls I see it has an @ after it adduser@ what does the @ mean? is there any workaround? I have root access, but I'm not a pro unix guy... (HowTos)