201

Preface

This is a fairly complex question related to the sudoers file and the sudo command in general.

NOTE: I have made these changes on a dedicated machine running Ubuntu Desktop 13.04, that I use purely for learning purposes. I understand it's a huge security risk to enable NOPASSWD sudo.

Question

Initially, my only change to the sudoers file (/etc/sudoers) was one line, a user specification that should have enabled nicholsonjf to run all commands with sudo without having to enter a password (see the line that starts with nicholsonjf):

# This file MUST be edited with the 'visudo' command as root.
#
# Please consider adding local content in /etc/sudoers.d/ instead of
# directly modifying this file.
#
# See the man page for details on how to write a sudoers file.
#
Defaults        env_reset
Defaults        mail_badpass
Defaults        secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"

# Host alias specification

# User alias specification

# Cmnd alias specification

# User privilege specification
root    ALL=(ALL:ALL) ALL
nicholsonjf    ALL=NOPASSWD: ALL

# Members of the admin group may gain root privileges
%admin ALL=(ALL) ALL

# Allow members of group sudo to execute any command
%sudo   ALL=(ALL:ALL) ALL

# See sudoers(5) for more information on "#include" directives:

#includedir /etc/sudoers.d

However this did not work, and I was still prompted for my password every time I ran a command as nicholsonjf. I was only able to start running sudo commands as nicholsonjf once I removed nicholsonjf from the sudo and admin groups.

Can anyone explain why this worked?

Is it because the user nicholsonjf was inheriting sudo rights from the two group specifications of admin and sudo (seen below in the sudoers file), which were overriding the nicholsonjf user specification because they were further down in the config file?

3

6 Answers 6

250

The line you added was overridden. From man sudoers:

When multiple entries match for a user, they are applied in order. Where there are multiple matches, the last match is used (which is not necessarily the most specific match).

In your case nicholsonjf was a member of the group sudo so for him this line applied:

%sudo   ALL=(ALL:ALL) ALL

If you want to override entries in /etc/sudoers just put the new entries after them.

The new entry should look like

myuser ALL=(ALL) NOPASSWD: ALL for a single user, or

%sudo ALL=(ALL) NOPASSWD: ALL for a group.

5
  • 8
    For a complete solution I would like to see something about NOPASSWD in this answer... Dec 5, 2014 at 15:08
  • 30
    I think, the solution should be: %sudo ALL=(ALL) NOPASSWD:ALL Dec 8, 2014 at 9:20
  • 5
    @DanielAlder: The specification line from the question nicholsonjf ALL=NOPASSWD: ALL is correct. It was just at a wrong place as I explained in the answer. ------ The Runas specification — in your case (ALL) — is optional. If you omit the specification you can run the commands as root and you cannot use -u and -g options of sudo. Dec 9, 2014 at 8:12
  • This is a worse security risk as it gives multiple users passwordless access. If it's your personal PC then that's not significant - perhaps. I'd just move the personal line, to last. Dec 9, 2014 at 8:15
  • 8
    An addition, rather than correction, if using something debian/ubuntu based (may be generally applied, not seen it elsewhere) Your absolute best-practice bet is to add custom commands to a file in /etc/sudoers.d/ and leave sudoers itself to be managed by the package manager.
    – Aquarion
    Nov 10, 2015 at 12:02
144

For a single user, add this line at the end of your sudoers file using the sudo visudo command:

superuser ALL=(ALL) NOPASSWD:ALL

For a group

%supergroup  ALL=(ALL) NOPASSWD:ALL
2
  • 8
    Before I read this answer I did %sudo ALL=NOPASSWD: ALL and it works. Am I the only one who finds Extended Backus-Naur Form really hard to understand?
    – Vince
    Jan 22, 2016 at 0:01
  • 4
    @Vince When used your command I can't sudo without password as user without sudo privileges. E.g. sudo -u root -i works, but sudo -u git -i doesn't. Dec 4, 2016 at 10:28
33

Run this command to never prompt the current user for a password when that user uses sudo:

echo "$USER ALL=(ALL:ALL) NOPASSWD: ALL" | sudo tee "/etc/sudoers.d/dont-prompt-$USER-for-sudo-password"

It creates a file called /etc/sudoers.d/dont-prompt-<YOUR USERNAME>-for-sudo-password with the following contents:

<YOUR USERNAME> ALL=(ALL:ALL) NOPASSWD: ALL

This works because Debian's and Ubuntu's default /etc/sudoers file has this line

#includedir /etc/sudoers.d

which makes it process files in /etc/sudoers.d. If the command above didn't work, check that no one has removed that line from your /etc/sudoers.

4
  • I like the shortcut working for the current user
    – cljk
    Sep 25, 2020 at 6:56
  • This is only way that worked here in Mint.
    – dawid
    Feb 7, 2021 at 14:07
  • This is actually "the" correct answer. Thanks! Apr 24 at 5:05
  • 1
    @MarcoMassenzio you're welcome, yea I felt like I was going a little crazy when I stumbled upon that directory and as I was writing this up because I'd been coming to this question every time I installed Ubuntu, everyone needs to do it, this is clearly the best way to do it over manually editing a file every time, it's been supported since the 90's and I've never seen anybody mention it anywhere else on the internet. Apr 24 at 5:15
2

As Vince has mentioned in a comment, you can use this line:

%sudo ALL=NOPASSWD: ALL

(This is different from the lines shown in those answers, and it solved the problem for me.)

5
  • 1
    @Eliah this is not that different from the other answers. All it does is replace the placeholder supergroup in Fedir's answer with sudo. What next, another user for the group wheel? Or any other group the user happens to be using?
    – muru
    Oct 4, 2017 at 11:19
  • 1
    @muru "All it does is replace the placeholder supergroup in Fedir's answer with sudo." What? Replacing supergroup with sudo in the line %supergroup ALL=(ALL) NOPASSWD:ALL yields %sudo ALL=(ALL) NOPASSWD:ALL, not %sudo ALL=NOPASSWD: ALL. Oct 4, 2017 at 11:21
  • Which is arguably worse, since now NOPASSWD is only for root as the target user. So, it doesn't even answer the question correctly!
    – muru
    Oct 4, 2017 at 11:26
  • @muru What is is not even arguably, however, is a substitution of supergroup with sudo. This is its own answer, not a thanks post or a copy of another answer. But yes, I agree: unless they intend that, this will not be as good for most users as the methods in the other answers. (But, especially considering the question says "all commands," not "all target users," I don't think this is in effect not even attempting to answer the question that was asked.) Oct 4, 2017 at 11:34
  • 1
    This worked for me and I wanted to share with other users :) (remove my comment if desired).
    – E. Fortes
    Oct 5, 2017 at 13:44
1

As I was researching this, I realized that there's a line in the /etc/sudoers file that is not a comment, but a directive that makes any file or folder under the directory /etc/sudoers/* override the contents of /etc/sudoers.

This is a sneaky little directive, as it appears to be a commented line upon first glance. It looks like this:

#includedir /etc/sudoers.d

This is how I've implemented the non-root, passwordless user in an ephemeral Docker Image for use in a CICD pipeline with the base image of ubuntu:18.04:

RUN \
  useradd -U foo -m -s /bin/bash -p foo -G sudo && passwd -d foo && passwd -d root && \
  sed -i /etc/sudoers -re 's/^%sudo.*/%sudo ALL=(ALL:ALL) NOPASSWD: ALL/g' && \
  sed -i /etc/sudoers -re 's/^root.*/root ALL=(ALL:ALL) NOPASSWD: ALL/g' && \
  sed -i /etc/sudoers -re 's/^#includedir.*/## Removed the #include directive! ##"/g' && \
  echo "Customized the sudoers file for passwordless access!" && \
  echo "foo ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers && \
  echo "root ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers && \
  echo "foo user:";  su foo -c 'whoami && id' && \
  echo "root user:"; su root -c 'whoami && id'

What happens with the above code:

  • The user and group foo is created.
  • The user foo is added to the both the foo and sudo group.
  • The home directory is set to /home/foo.
  • The shell is set to /bin/bash.
  • The sed command does inline updates to the /etc/sudoers file to allow foo and root users passwordless access to the sudo group.
  • The sed command disables the #includedir directive that would allow any files in subdirectories to override these inline updates.
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  • 1
    You don't need to remove the directive if you don't have any files in that directory. Jan 4 at 19:58
  • 1
    Thank you for the comment. The reason I've "disabled" this directive in the above snippet is to make certain the script works. Great callout though for those unaware Feb 2 at 17:23
0

One can insert a string in one line without EOF formatting at end of sudoers file or remove with sed -i:

cat >> /etc/sudoers <<<'PaSe ALL=(ALL:ALL) NOPASSWD:ALL'

Reference: https://stackoverflow.com/questions/41298208/how-to-append-a-line-at-the-end-of-etc-sudoers-file-using-shell-script-without/70039824#70039824

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