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Vivek Sharma
Asked: 2020-01-15 00:10:05 +0800 CST

Want to understand this permission of /usr/bin/sudo

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I was getting below error while running command sudo -s after changing the permission to 777 of /usr/bin/sudo

sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set

Ii solved this by below process:

Select your OS version in (recovery mode), and press Enter Key.

Ex : Ubuntu 14.04 (recovery mode)

It will bring you up another screen. Now select “Drop to root shell prompt” and press Enter.

It will load a command line at the bottom of the screen.

Now run each of the following commands.

mount -o remount,rw /

mount –all

chown root:root /usr/bin/sudo

chmod 4755 /usr/bin/sudo

restart

Now, I just want to understand why it was not working with 777 permission on /usr/bin/sudo

Please explain, thanks in advance.

command-line sudo

2 Answers

  1. I'm pretty sure this is a simple security feature where if the /usr/bin/sudo has different permissions to 755 it will become inaccessible. I couldn't find an article to confirm this so I'd say this is my guess. However you can find a lot of people asking the same thing an always everyone telling them to revert to 755 permissions

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  2. Best Answer

    sudo has the "setuid" bit (the 4 in chmod 4755). It means that when you execute sudo, you automatically get the privileges of sudo's owner, which is root. So any execution of sudo has root privileges, it's just that the first thing the "official" version does is asking for a password to determine it it can continue.

    If sudo is word-writable, then anyone can patch it to not check passwords or do other things, and so gain access to root privileges. So sudo must be kept R/O for everyone otherwise it should be considered as compromised.

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