How a non-root user sudo to another non-root user without password?

Question

As root, created a new non-root user on RHEL 7.5

appuser:x:1903:1903:appuser:/home/appuser:/bin/bash

A non-root user to be able to sudo to appuser,

sudo -u appuser

without a password,

What are the changes required on RHEL 7.5?

Solution

You can edit the "User privilege specification" section of /etc/sudoers, adding:

non-root-user ALL = (appuser) NOPASSWD: ALL

This will allow non-root-user to run all commands as appuser. non-root-user will not be allowed to run commands as root.

Note that errors in /etc/sudoers can make a system unusable. The file should only be edited with:

$ sudo visudo

This special editor checks the sudoers file for errors before saving and refuses to save it if errors are found.

Comments

[overexchange]

But -r--r----- 1 root root 1225 Jun 12 12:04 /etc/sudoers. Do you think this is customised permision?

[overexchange]

E45 error on modifying the file with vi editor

[fra-san]

It looks like -r--r----- is the standard file mode for /etc/sudoers. Refer to my edited answer for how to edit it.

[Sridhar Sarnobat]

This still gives visudo: /etc/sudoers: Permission denied if I do not have root privileges, so I don't see how this answers the question.

[fra-san]

@SridharSarnobat The sudo visudo part is just a clarification on how to (safely) edit /etc/sudoers, i.e. how to configure the system so that an unprivileged user can authenticate as another unprivileged user without being prompted for a password. That step requires root access, of course (and the OP does have it). Apparently, the question is not about how to configure a non-root user using a non-root user. Does this clear your doubts?

[Sridhar Sarnobat]

Fair enough, my case isn't quite the same as the OP. I don't have the ability to temporarily use root permissions so I guess I'm out of luck. This seems like a bit of a flaw in Linux's model.