10 Useful Sudoers Configurations for Setting ‘sudo’ in Linux

In Linux and other Unix-like operating systems, only the root user can run all commands and perform certain critical operations on the system such as install and update, remove packages, create users and groups, modify important system configuration files and so on.

However, a system administrator who assumes the role of the root user can permit other normal system users with the help of sudo command and a few configurations to run some commands as well as carry out a number of vital system operations including the ones mentioned above.

Alternatively, the system administrator can share the root user password (which is not a recommended method) so that normal system users have access to the root user account via su command.

sudo allows a permitted user to execute a command as root (or another user), as specified by the security policy:

  1. It reads and parses /etc/sudoers, looks up the invoking user and its permissions,
  2. then prompts the invoking user for a password (normally the user’s password, but it can as well be the target user’s password. Or it can be skipped with NOPASSWD tag),
  3. after that, sudo creates a child process in which it calls setuid() to switch to the target user
  4. next, it executes a shell or the command given as arguments in the child process above.

Below are ten /etc/sudoers file configurations to modify the behavior of sudo command using Defaults entries.

$ sudo cat /etc/sudoers
/etc/sudoers File
# 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"
Defaults	logfile="/var/log/sudo.log"
Defaults	lecture="always"
Defaults	badpass_message="Password is wrong, please try again"
Defaults	passwd_tries=5
Defaults	insults
Defaults	log_input,log_output

Types of Defaults Entries

Defaults                parameter,   parameter_list     #affect all users on any host
Defaults@Host_List      parameter,   parameter_list     #affects all users on a specific host
Defaults:User_List      parameter,   parameter_list     #affects a specific user
Defaults!Cmnd_List      parameter,   parameter_list     #affects  a specific command 
Defaults>Runas_List     parameter,   parameter_list     #affects commands being run as a specific user

For the scope of this guide, we will zero down to the first type of Defaults in the forms below. Parameters may be flags, integer values, strings, or lists.

You should note that flags are implicitly boolean and can be turned off using the '!' operator, and lists have two additional assignment operators, += (add to list) and -= (remove from list).

Defaults     parameter
Defaults     parameter=value
Defaults     parameter -=value   
Defaults     parameter +=value  
Defaults     !parameter       

1. Set a Secure PATH

This is the path used for every command run with sudo, it has two importances:

  1. Used when a system administrator does not trust sudo users to have a secure PATH environment variable
  2. To separate “root path” and “user path”, only users defined by exempt_group are not affected by this setting.

To set it, add the line:

Defaults secure_path="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/snap/bin"

2. Enable sudo on TTY User Login Session

To enable sudo to be invoked from a real tty but not through methods such as cron or cgi-bin scripts, add the line:

Defaults  requiretty   

3. Run Sudo Command Using a pty

A few times, attackers can run a malicious program (such as a virus or malware) using sudo, which would again fork a background process that remains on the user’s terminal device even when the main program has finished executing.

To avoid such a scenario, you can configure sudo to run other commands only from a psuedo-pty using the use_pty parameter, whether I/O logging is turned on or not as follows:

Defaults  use_pty

4. Create a Sudo Log File

By default, sudo logs through syslog(3). However, to specify a custom log file, use the logfile parameter like so:

Defaults  logfile="/var/log/sudo.log"

To log hostname and the four-digit year in the custom log file, use log_host and log_year parameters respectively as follows:

Defaults  log_host, log_year, logfile="/var/log/sudo.log"

Below is an example of a custom sudo log file:

Create Custom Sudo Log File
Create Custom Sudo Log File

5. Log Sudo Command Input/Output

The log_input and log_output parameters enable sudo to run a command in pseudo-tty and log all user input and all output sent to the screen receptively.

The default I/O log directory is /var/log/sudo-io, and if there is a session sequence number, it is stored in this directory. You can specify a custom directory through the iolog_dir parameter.

Defaults   log_input, log_output

There are some escape sequences are supported such as %{seq} which expands to a monotonically increasing base-36 sequence number, such as 000001, where every two digits are used to form a new directory, e.g. 00/00/01 as in the example below:

$ cd /var/log/sudo-io/
$ ls
$ cd  00/00/01
$ ls
$ cat log
Log sudo Input Output
Log sudo Input Output

You can view the rest of the files in that directory using the cat command.

6. Lecture Sudo Users

To lecture sudo users about password usage on the system, use the lecture parameter as below.

It has 3 possible values:

  1. always – always lecture a user.
  2. once – only lecture a user the first time they execute sudo command (this is used when no value is specified)
  3. never – never lecture the user.
Defaults  lecture="always"

Additionally, you can set a custom lecture file with the lecture_file parameter, type the appropriate message in the file:

Defaults  lecture_file="/path/to/file"
Lecture Sudo Users
Lecture Sudo Users

7. Show Custom Message When You Enter Wrong sudo Password

When a user enters a wrong password, a certain message is displayed on the command line. The default message is “sorry, try again”, you can modify the message using the badpass_message parameter as follows:

Defaults  badpass_message="Password is wrong, please try again"

8. Increase sudo Password Tries Limit

The parameter passwd_tries is used to specify the number of times a user can try to enter a password.

The default value is 3:

Defaults   passwd_tries=5 
Increase Sudo Password Attempts
Increase Sudo Password Attempts

To set a password timeout (default is 5 minutes) using passwd_timeout parameter, add the line below:

Defaults   passwd_timeout=2

9. Let Sudo Insult You When You Enter Wrong Password

In case a user types a wrong password, sudo will display insults on the terminal with the insults parameter. This will automatically turn off the badpass_message parameter.

Defaults  insults 
Let's Sudo Insult You When Enter Wrong Password
Let’s Sudo Insult You When Enter Wrong Password

Read More: Let Sudo Insult You When You Enter Incorrect Password

10. Learn More Sudo Configurations

Additionally, you can learn more sudo command configurations by reading: Difference Between su and sudo and How to Configure sudo in Linux.

That’s it! You can share other useful sudo command configurations or tricks and tips with Linux users out there via the comment section below.

Hey TecMint readers,

Exciting news! Every month, our top blog commenters will have the chance to win fantastic rewards, like free Linux eBooks such as RHCE, RHCSA, LFCS, Learn Linux, and Awk, each worth $20!

Learn more about the contest and stand a chance to win by sharing your thoughts below!

Aaron Kili
Aaron Kili is a Linux and F.O.S.S enthusiast, an upcoming Linux SysAdmin, web developer, and currently a content creator for TecMint who loves working with computers and strongly believes in sharing knowledge.

Each tutorial at TecMint is created by a team of experienced Linux system administrators so that it meets our high-quality standards.

Join the TecMint Weekly Newsletter (More Than 156,129 Linux Enthusiasts Have Subscribed)
Was this article helpful? Please add a comment or buy me a coffee to show your appreciation.


Leave a Reply
  1. Hello Aaron, thank you for sharing this info on sudo configuration. Is there a way for sudo to record tty commands run by a ldap user after sudo to a service account and store them to a file?


    [user@test1] / # sudo su - oracle
    [oracle@test1] /home/oracle # hostname
    [oracle@test1] /home/oracle # pwd

    How would I let sudo store these commands (hostname, pwd, etc) to a file after a user sudo to service account (oracle, etc) and run commands as that service account on a server? I have an audit requirement on AIX 7.2 servers to capture all TTY session commands run by a user after sudo to a service account hosted on each server.

    Thank you for your time.

    Thank you.

    • @Ashok,

      First, create a log directory and set the sticky bit on it.

      # mkdir -p /var/log/users_historylogs/
      # chmod +t  /var/log/users_historylogs/ 

      Next, create a new script file under /etc/profile.d/ directory.

      # vi /etc/profile.d/history_log.sh

      And add the below content at the bottom, save, and exit.

      _who_am_i=$(whoami|awk '{print $1}')
      _ID=$(id -u $_who_am_i)
      if [ "$_ID" > 0 ]
      export HISTSIZE=10000
      export HISTTIMEFORMAT='%F %T '
      export HISTFILE=/var/log/users_historylogs/history-users-$(whoami | awk '{print $1}';exit)-$(date +%F)
      export PROMPT_COMMAND='history -a'

      Set the permission and enable the script.

      # chmod 770 /etc/profile.d/history_log.sh
      # source /etc/profile.d/history_log.sh

      Now all user executed commands history saved to log file…

      • Hi Ravi,

        Thank you so much for the quick response. Does the same procedure apply on AIX 7.2 servers since it uses Korn shell by default? I see that the /etc/profile.d directory does not exist on AIX servers and I have implemented step 1 by adding those lines in /etc/profile to set up secondary logging for root which looks good as the file was created, not sure if I should add commands to the same /etc/profile file to setup secondary logging for other users except root. Thank you.

      • This is a minor typo.

        $(who am i | awk '{print $1}';exit)

        should be:

        $(whoami | awk '{print $1}';exit)

        Fantastic. Thank you for this script.

    • @Ryan

      Great! We are grateful that this has helped you gain more knowledge about Linux. Many thanks for the useful feedback.

  2. Hi,

    Thanks for the nice overview.

    Can you help with this?

    I want to mount a special source without root privileges. So I made an entry in the /ect/sudoers file:

    username       ALL = NOPASSWD: /sbin/mount.cifs, /bin/umount /mnt/folder

    How can I restrict the source that I want to mount to be only one that can be mounted. Now username can mount everything.

    Thanks in advance.


    • I think what you may want to do is, instead of using sudo, add the mount to /etc/fstab, and include the option “user” (see the man page on “mount”). What this will do is allow ordinary users to mount/unmount the filesystem. That would allow ALL users to mount/unmount it. They can then say “mount /mnt/folder“. This mount option is specific to Linux and would not work on other flavors of Unix.

      Another option would be to use the automounter. You could setup a direct automount map. Then whenever a user does “cd /mnt/folder“, it mounts. After it mounts, every 5 minutes, it half-heartedly attempts to unmount it, which will not be successful if it is still in use. Again, this would allow ALL users to mount it.

      If you really want just the one user to be able to mount/unmount, then you’d need to spell out the full mount command (not /sbin/mount.cifs):

      user ALL = NOPASSWD: /bin/mount /path-to-device /mnt/folder, /bin/umount /mnt/folder

      (there might be some options you’ll want to specify after “mount”, e.g. “-o ro”, “-t cifs”, etc.). The user will then need to type the command-line exactly as it appears in sudoers (if they are not that savvy, create them an alias).


Got Something to Say? Join the Discussion...

Thank you for taking the time to share your thoughts with us. We appreciate your decision to leave a comment and value your contribution to the discussion. It's important to note that we moderate all comments in accordance with our comment policy to ensure a respectful and constructive conversation.

Rest assured that your email address will remain private and will not be published or shared with anyone. We prioritize the privacy and security of our users.