How to Handle Sudo Password Prompts in SSH Here-Documents When No TTY is Present


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When executing remote commands via SSH using here-documents, you might encounter the frustrating message:

sudo: no tty present and no askpass program specified

This typically happens when:

  • Running sudo commands that require password input
  • Using SSH command redirection with << syntax
  • The remote system's sudoers configuration requires TTY

The common solution of using ssh -t works for single commands:

ssh -t example.com "sudo service apache2 restart"

But fails in here-document context because:

ssh -t example.com <

The TTY allocation gets lost during the here-document processing.

Solution 1: Force TTY Allocation Properly

Use multiple -t flags (recommended for most cases):

ssh -tt example.com <<'END_COMMANDS'
sudo /etc/init.d/apache2 reload
END_COMMANDS

The double -t (-tt) forces TTY allocation even when stdin isn't a terminal.

Solution 2: Configure Sudoers (Permanent Fix)

Edit /etc/sudoers on the remote server:

Defaults:username !requiretty
username ALL=(ALL) NOPASSWD: /etc/init.d/apache2

Solution 3: SSH Command Chaining

For complex multi-command operations:

ssh -t example.com "
sudo -S << 'EOF' /etc/init.d/apache2 reload
your_password
EOF
"

When dealing with configuration files and multiple commands:

read -r -d '' COMMANDS <<-'EOC'
sudo service apache2 stop
sudo cp /tmp/config.conf /etc/apache2/
sudo service apache2 start
EOC

ssh -tt user@example.com "$COMMANDS"
  • Never hardcode passwords in scripts
  • Consider using SSH certificates instead of password auth
  • Limit sudo permissions in /etc/sudoers
  • For automation, use dedicated service accounts

For complex interactive sessions:

#!/usr/bin/expect -f
spawn ssh -t user@example.com
expect "password:"
send "$env(SSH_PASSWORD)\r"
expect "$ "
send "sudo service apache2 restart\r"
expect "password for user:"
send "$env(SUDO_PASSWORD)\r"
expect eof

When automating server administration through SSH, many developers prefer using here-documents for multi-line command execution. However, this approach breaks when commands require terminal interaction - particularly with sudo operations.

ssh user@server <

Results in the frustrating error:

sudo: no tty present and no askpass program specified

While ssh -t works for single commands:

ssh -t user@server "sudo reboot"

The same approach fails with here-documents because SSH allocates the TTY before processing the input stream:

# Still fails
ssh -t user@server <

Option 1: Force TTY Allocation Properly

Use double -t flags to force TTY allocation:

ssh -tt user@server <<'END_SSH'
sudo systemctl restart postgresql
END_SSH

Option 2: Configure Passwordless Sudo

For automated scripts, consider configuring sudoers to skip password prompts:

# In /etc/sudoers on the target machine
%admin ALL=(ALL) NOPASSWD: /usr/bin/systemctl restart nginx

Option 3: Use SSH Config

Add this to your ~/.ssh/config:

Host myserver
  HostName server.example.com
  RequestTTY force

For scripts requiring multiple privileged commands:

ssh -tt admin@dbserver <<'EOSSH'
sudo -u postgres psql <<'EOPGSQL'
CREATE DATABASE new_app;
GRANT ALL ON DATABASE new_app TO app_user;
EOPGSQL
sudo systemctl restart postgresql
EOSSH

When using forced TTY allocation:

  • Avoid storing sensitive commands in scripts
  • Use SSH certificates instead of passwords
  • Consider implementing command whitelisting in sudoers