sudo voodoo

[Trevor]

Hello all,

Time for a little something to stretch the mind.  Had a little situation involving the "sudo" mechanism.  

I was doing a litlle work with kernel tunables, and was attempting to modify one of the tunables by adding a file to the /etc/sysctl.d directory.  When executing my commands, I was logged as a non-privileged user.  However, I promise you, I have my sudo configuration setup properly.  I've executed commands with the greatest of ease using "sudo", until I was blind-sided with not being able to perform a task which definitely qualifies - at least I thought so - as "low-hanging fruit".

Okay, already someone is saying that my "sudo" config is not setup properly.  I get it - end users are NOT to be trusted    So, here's my entry in my /etc/sudoers file:

            ec2-user  ALL=(ALL)   NOPASSWD:  ALL

Now, here's the command that I executed, that is prompting this post:

$  sudo echo   vm.swappiness=42   >>   /etc/sysctl.d/swap.conf
-bash: /etc/sysctl.d/swap.conf: Permission denied

Whooooooooa!  Stop the presses!!!  What's going on here?   

Okay, so the first elementary thing to look at is the permission settings on the /etc/sysctl.d directory:     

      drwxr-xr-x. 2 root root 41 Dec 12 19:55 /etc/sysctl.d

Okay, so the permissions on the directory are not an issue.

I promise, the issue is NOT with my sudoers file!!!!  It's not something quirky involving kernel tunables and/or the /etc/sysctl.d directory.  Okay, that's all I'm  guaranteeing.   I don't want to lead you in any particular direction.  I'll say this much, don't put your focus on anything related to kernel tunables.  Alright, I've said enough

My question: Where's the issue?   What's the problem?

[Fran_Garcia]

hi there

This is a known gotcha of sudo / bash shell interaction . Your echo is indeed run by root with sudo, but your file redirection (>>  /etc/sysctl.d/swap.conf) is not, because that's processed in the context of the user that runs the current bash process.

A workaround for that is:

echo "content" | sudo tee -a /etc/foo.conf

In this case, the writing is performed by tee, which is run by root

Hope this helps!

Fran

[Trevor · Accepted solution]

Ding!  Ding!  Ding!

That's great work Fran!!!  You get the prize!!!
I'm not sure what it is just yet, but you get it

Your response is definitely one approach to
the resolution.  Great work!!!

[EmanuelHaine · Accepted solution]

@Trevor

Thanks for bringing this question to the Learn Platform.

@Fran_Garcia 

Great answer. I wasn't aware of that. In fact, I haven't had a situation like this.

I was taking a look at sudo's man page and I saw another way for this case:

sudo bash -c "echo vm.swappiness=42 >> /etc/sysctl.d/swap.conf"

It's the same concept with a different code.

[Trevor]

Ding!  Ding!  Ding!

Gotta ring the bell for you as well Emanuel!!!  
Your solution is right on point!!!

Thank you for taking the time to look at the
post, and for providing a solution.

Hope you're safe and well!!!