问nodeJS exec不适用于"cd“外壳命令

EN

var sys = require('sys'),
    exec = require('child_process').exec;

exec("cd /home/ubuntu/distro", function(err, stdout, stderr) {
        console.log("cd: " + err + " : "  + stdout);
        exec("pwd", function(err, stdout, stderr) {
            console.log("pwd: " + err + " : " + stdout);
            exec("git status", function(err, stdout, stderr) {
                console.log("git status returned " ); console.log(err);
            })
        })
    })

cd: null :

pwd: null : /

git status returned 
{ [Error: Command failed: fatal: Not a git repository (or any of the parent directories): .git ] killed: false, code: 128, signal: null }