root privilege with su
<p>I am using su , busybox on android device. 
but on doing "su", it seems that I have no root privilege: </p>

<pre><code>shell@nemo:/ $ su
1|shell@nemo:/ $

1|shell@nemo:/ $ whoami
shell
shell@nemo:/ $
</code></pre>

<p><strong>EDIT1</strong>:</p>

<p>Seems like the privileged in su are OK. please see below , from adb shell: shell@nemo:/system/xbin $ ls -al su -rwxr-xr-x root root 75364 2015-11-21 13:10</p>

<p><strong>EDIT2</strong>:</p>

<p>I've set 7777 permission (suid), but it still fails.</p>

<pre><code>chmod 7777 su-arm

 shell@nemo:/ $ ls -al /system/xbin/su-arm
-rwsrwsrwt root     shell      467952 2016-11-20 12:01 su-arm
shell@nemo:/ $ su-arm
255|shell@nemo:/ $ id
uid=2000(shell) gid=2000(shell) groups=2000(shell),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats) context=u:r:shell:s0
shell@nemo:/ $whoami
shell
</code></pre>

<p><strong>EDIT3:</strong>
I've updated su binary and busybox binary, but each now fails differently:</p>

<pre><code>shell@nemo:/ $ busybox su
su: unknown user root
1|shell@nemo:/ $ su
error: only position independent executables (PIE) are supported.
1|shell@nemo:/ $
</code></pre>

<p>How can I understand what's wrong with su and how to fix it ?</p>

<p>Thanks,
Ranchu</p>