How to fix the "sudo: no tty present and no askpass program specified" error

A tty is a terminal required if a program needs to receive user input, such as when entering a password for sudo.

Running a script via SSH that asks for sudo's password will get you the following sudo: no tty present and no askpass program specified error, as no tty is allocated by default for an automated SSH session. You might also run into a terminal is required to read the password when doing the same.

$ ssh user@simplified.guide -- sudo ls
user@simplified.guide's password:
sudo: no tty present and no askpass program specified

sudo: a terminal is required to read the password; either use the -S option to read from standard input or configure an askpass helper

You can avoid both no tty present and no askpass program specified and a terminal is required to read the password errors when running sudo via SSH by configuring the SSH client and sudo.

1. Allocate pseudo terminal when connecting via SSH.

   $ ssh -t user@example.com -- sudo id
   user@example.com's password:
   [sudo] password for user:
   uid=0(root) gid=0(root) groups=0(root)
   Connection to example.com closed.

   -t      Force pseudo-terminal allocation.  This
           can be used to execute arbitrary screen-
           based programs on a remote machine, which
           can be very useful, e.g. when implement-
           ing menu services.  Multiple -t options
           force tty allocation, even if ssh has no
                local tty.

2. Force sudo to read the password from stdin by using --stdin or -S switch.

   $ ssh user@example.com -- sudo -S id
   user@example.com's password:
   [sudo] password for user: pass
   uid=0(root) gid=0(root) groups=0(root)

   Your password will be displayed on the stdout and could pose a securitk risk. pass is the password in this example.

   -S, --stdin Write the prompt to the standard
               error and read the password from
               the standard input instead of using
               the terminal device.

3. Configure passwordless sudo for the user and command on the SSH server.

   $ ssh user@example.com -- sudo id
   user@example.com's password:
   uid=0(root) gid=0(root) groups=0(root)

   Related: How to set up passwordless sudo in Linux