有关于android 调用外部命令问题（Runtime.getRuntime().exec参数）

android 调用外部命令的问题（Runtime.getRuntime().exec参数）
调用ls还有cat命名是没问题的，但是有些命令用不了，例如ll，打印显示环境有问题，不知道怎么解？

代码：

 private String ssss() {
 String TAG2 = "CMD";
 try {
    String  cmd="ls";
    Process process =Runtime.getRuntime().exec(cmd);
    InputStream in1 = process.getInputStream();
    BufferedReader reader1 = new BufferedReader(new InputStreamReader(in1));
    String line1;
    Log.i(TAG2, "返回结果" + reader1.readLine());
    while ((line1 = reader1.readLine()) != null) {

        Log.i(TAG2, "返回结果=" + line1);
    }
    in1.close();
} catch (IOException ex) {
    ex.printStackTrace();
    //  result2 = "N/A";
}
return null;


}

String cmd="ls"打印结果：

 644-644/com.example.MEM I/CMD﹕ 返回结果acct
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=config
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=d
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=default.prop
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=etc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.goldfish.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.recovery.sun7i.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.sdb.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.sdd.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.sun7i.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=init.trace.rc
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=initlogo.rle
 03-23 16:42:56.157 644-644/com.example.MEM I/CMD﹕ 返回结果=nand.ko
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=proc
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=sbin
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=sun7i-ir.ko
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=system
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=ueventd.goldfish.rc
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=ueventd.sun7i.rc
 03-23 16:42:56.167 644-644/com.example.MEM I/CMD﹕ 返回结果=null

String cmd="ll"打印结果：

 03-23 16:46:52.337 3166-3166/com.example.MEM W/System.err﹕ java.io.IOException: Error running exec(). Command: [ll] Working Directory: null Environment: null
 03-23 16:46:52.337 3166-3166/com.example.MEM W/System.err﹕ at java.lang.ProcessManager.exec(ProcessManager.java:211)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at java.lang.Runtime.exec(Runtime.java:168)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at java.lang.Runtime.exec(Runtime.java:241)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at java.lang.Runtime.exec(Runtime.java:184)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at com.example.MEM.MyActivity.ssss(MyActivity.java:464)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at com.example.MEM.MyActivity.access$000(MyActivity.java:32)
 03-23 16:46:52.347 3166-3166/com.example.MEM W/System.err﹕ at com.example.MEM.MyActivity$1.onClick(MyActivity.java:90)