Sudo: No Tty Present And No Askpass Program Specified

“sudo no tty present and no askpass program specified” is an error message that appears when you try to run the “sudo” command in a non-interactive environment. The “sudo” command is used to run a command with superuser (i.e., “root”) privileges, but it requires a terminal (i.e., a “tty”) to be present to prompt the user for their password.

If a terminal is not present, and no “askpass” program is specified, the “sudo” command will fail with this error message. If this occurs, sudo will terminate with this error message. This article explains why sudo fails with this error message and how it can be fixed.

What are sudo, tty, and askpass?

Sudo stands for ‘Super User Do.’ It is a command-line program for Unix-like computer systems that allow users to execute programs with the security privileges of another user.

In other words, it is a command that administrators can use to run commands as if they were the root user (a.k.a. “superuser”).

When you execute ‘sudo’ followed by a command or series of commands, your process will have elevated privileges on Linux-based systems such as Ubuntu.

A TTY is an abbreviation for Teletype, which we now call computer terminals with keyboard input/output devices. On modern operating systems, there isn’t a need for these anymore because most people use their computers remotely through a terminal emulator.

An askpass program is a tool that can be used by the sudo command to prompt for your password without revealing it on the screen in plain text, which would defeat any security measures set up and could allow someone else to enter commands as if they were you with elevated privileges.

How to Fix sudo: no tty present and no askpass program specified

To fix this error, you can try a few different things:

1. Make sure you’re running the “sudo” command in a terminal. If you’re trying to run the command over an SSH connection, ensure you’re connected to a terminal session (e.g., using “ssh -t”).
2. Check that the “askpass” program is installed on your system. “askpass” is a program that provides a graphical user interface (GUI) for entering the user’s password when running the “sudo” command in a non-interactive environment. On Ubuntu and Debian, you can install it by running “sudo apt-get install libpam-ssh-agent-auth”. You can install it on Red Hat and Fedora by running “sudo yum install ssh-askpass”.
3. Check the value of the “SUDO_ASKPASS” environment variable. It should point to the location of the “askpass” program. If it’s not set, you can set it by running “export SUDO_ASKPASS=/usr/bin/ssh-askpass” (assuming “ssh-askpass” is installed in that location).
4. Make sure that the user running the command has a terminal. This can be done by running the command “sudo -i” which will start a new shell session with superuser privileges and a tty is present.
5. Ensure that the user has permission to run the command with superuser privileges. This can be done by checking the user’s permissions in the /etc/sudoers file.

It’s worth noting that, depending on your specific use case, there may be alternative ways to achieve the same goal without using the “sudo” command in a non-interactive environment. For example, you can use the “su” command to switch to the superuser account or “sudo -s” to start a new shell session with superuser privileges.

Another alternative is to use “sudo -u” to run a command as a specific user, rather than the superuser. This can be useful if you need to run a command with elevated privileges, but you don’t want to run it as the superuser.

It’s also important to remember that running commands with superuser privileges carries a certain level of risk. If you’re not careful, you can accidentally damage your system or expose it to security vulnerabilities. That’s why it’s always a good idea to be cautious when using the “sudo” command, and to make sure you understand what the command is doing before you run it.

What is a sudoers file?

The sudoers file is a configuration used to configure sudo in Linux. The sudoers configuration file is located at /etc/sudoers.

The sudoer configuration file is parsed in textual order, so it starts to parse from top to bottom of the document. The first match found will be used for sudo command request.

The sudoers file must be edited by running

$ sudo visudo

For example, suppose you want to give user larry permission to shutdown a machine. Without the sudo permission, larry would see this error message:

$ sudo shutdown
[sudo] password for larry:
Sorry, user larry is not allowed to execute '/usr/sbin/shutdown' as root on mars.planet.com.

To give user larry the ability to shutdown the machine, add the line below to the sudoers file:

larry ALL=(ALL) NOPASSWD: /sbin/shutdown

When user larry logs in to the machine, he can run the sudo command to shutdown the machine as shown below.

$ sudo shutdown now

The machine is shutdown automatically.

Why does sudo fail with this error message ‘sudo: no tty present and no askpass program specified’?

Error ‘sudo: no tty present and no askpass program specified’ means you cannot use sudo unless someone logged in as root or the user has been granted permission to run commands without a password for this session.

If you want to sudo without a password, then it is likely that your sudoers file does not have the NOPASSWD setting enabled. To resolve this, adjust your permissions as shown above.

If you have the NOPASSWD configured and you still get this error when executing a command, it might be because you are not running it with a tty. This might happen if you connect to your machine over SSH, or if you run the command from inside of a crontab.

If the error happens when using SSH, you need to use the ‘ssh -t‘ option. This will provide a shell with a ‘pseudo-tty’ and fix the problem.

$ ssh -t mars "sudo shutdown now"

In this example, you SSH to remote machine mars so you can do a shutdown. The -t option forces a pseudo-tty allocation, allowing you to run arbitrary commands on a remote machine.

What are the Best Practices When Using the “sudo” Command?

When using the “sudo” command, it’s best practice to:

• Only run commands that you understand and know what they do
• Be cautious when running commands that could potentially damage your system
• Always use the full path to the command, so that you don’t accidentally run a different command with the same name
• Avoid using wildcards when running commands with “sudo” to prevent unintended execution.
• Use “sudo -l” to check which commands are allowed to run as superuser before executing any command.

Conclusion

“sudo no tty present and no askpass program specified” is an error message that appears when you try to run the “sudo” command in a non-interactive environment. The error message occurs when the “sudo” command requires a terminal (i.e., a “tty”) to be present to prompt the user for their password, but a terminal is not present.

To troubleshoot this error, try installing the “askpass” program, check the value of the “SUDO_ASKPASS” environment variable, make sure that the user running the command has a terminal, or check the user’s permissions. As an alternative, you can use “su” command, “sudo -s” or “sudo -u.”

Frequently Asked Questions