Linux sendmail

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The error message "sh: 1: /usr/sbin/sendmail: not found" indicates that the system cannot locate the sendmail executable at the specified path (/usr/sbin/sendmail). This is a common issue and usually means one of the following:

• sendmail (or another MTA) is not installed.
• A different MTA (like Postfix or Exim) is installed, and its sendmail compatibility binary is not linked or is in a different location.
• The PHP sendmail_path in php.ini is pointing to an incorrect location.

Here's a step-by-step approach to diagnose and fix this:
Step 1: Check if sendmail (or another MTA) is installed
First, let's see if sendmail or a common alternative like postfix or exim4 is already present on your system.
On Debian/Ubuntu:

1. dpkg -l | grep sendmail
2. dpkg -l | grep postfix
3. dpkg -l | grep exim4

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On CentOS/RHEL:

1. rpm -qa | grep sendmail
2. rpm -qa | grep postfix
3. rpm -qa | grep exim

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If none of these commands return any installed packages, it's highly likely you don't have an MTA installed.
Step 2: Install an MTA (if not already installed)
It's generally recommended to use postfix for a simpler setup, as sendmail can be quite complex to configure from scratch. However, if you specifically want sendmail, you can install it.
For Debian/Ubuntu (recommended: Postfix for ease of use):

1. sudo apt update
2. sudo apt install postfix mailutils

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During the Postfix installation, you'll usually get a configuration screen. Choose "Internet Site" for general email sending and follow the prompts, providing your system's hostname/domain if asked. mailutils provides the mail command, which often creates a symbolic link from /usr/bin/mail to the system's MTA.
Alternatively, to install Sendmail (more complex configuration):

1. sudo apt update
2. sudo apt install sendmail
3. sudo sendmailconfig # Follow the interactive prompts to configure it.

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For CentOS/RHEL (recommended: Postfix):

1. sudo yum update
2. sudo yum install postfix mailx
3. sudo systemctl enable postfix
4. sudo systemctl start postfix

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You might also need to configure your firewall to allow SMTP traffic:

1. sudo firewall-cmd --add-service=smtp --permanent
2. sudo firewall-cmd --reload

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Alternatively, to install Sendmail:

1. sudo yum update
2. sudo yum install sendmail sendmail-cf
3. sudo systemctl enable sendmail
4. sudo systemctl start sendmail

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Again, configure your firewall if necessary for port 25.
Step 3: Verify the sendmail path and create a symbolic link (if necessary)
Even if Postfix or Exim is installed, many applications (including PHP's mail() function) expect to find a sendmail executable at /usr/sbin/sendmail. Often, the installed MTA provides a compatibility binary or wrapper at that location.
Check if the sendmail command exists and where it points:

1. which sendmail
2. ls -l /usr/sbin/sendmail

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If which sendmail returns nothing, or ls -l /usr/sbin/sendmail shows it doesn't exist or is a broken link, and you have Postfix or Exim installed, you might need to create a symbolic link:
If Postfix is installed:

1. sudo ln -s /usr/sbin/sendmail.postfix /usr/sbin/sendmail

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(Sometimes it's just /usr/sbin/postfix, so you might also try sudo ln -s /usr/sbin/postfix /usr/sbin/sendmail if sendmail.postfix doesn't exist.)
If Exim is installed:

1. sudo ln -s /usr/sbin/exim4 /usr/sbin/sendmail

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(Or check ls -l /usr/sbin/sendmail* to see what compatibility link Exim might provide.)
Step 4: Check PHP's sendmail_path in php.ini
If you've installed an MTA and confirmed the sendmail executable path, ensure PHP is configured to use it.

• Find your php.ini:
  
  1. php -i | grep "Loaded Configuration File"

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  This will show you the path to the php.ini file that PHP is currently using. Common locations include /etc/php/X.Y/cli/php.ini (for command line) and /etc/php/X.Y/fpm/php.ini or /etc/php/X.Y/apache2/php.ini (for web server).
• Edit php.ini:Open the php.ini file with a text editor (e.g., sudo nano /etc/php/X.Y/cli/php.ini) and search for sendmail_path. Make sure it's uncommented and points to the correct location (usually /usr/sbin/sendmail -t -i):
  sendmail_path = /usr/sbin/sendmail -t -i[/code]If you're using a different MTA that doesn't provide a /usr/sbin/sendmail compatibility link, you might point it directly to the MTA's binary, e.g., sendmail_path = /usr/sbin/postfix -t -i. However, creating the symbolic link is generally the cleaner solution.
• Restart PHP-FPM or Apache/Nginx (if running web server PHP):After modifying php.ini, you must restart your web server or PHP-FPM service for the changes to take effect.
  
  
  • For Apache: sudo systemctl restart apache2 or sudo service apache2 restart
  • For Nginx with PHP-FPM: sudo systemctl restart phpX.Y-fpm (replace X.Y with your PHP version, e.g., php8.2-fpm) or sudo service phpX.Y-fpm restart

Step 5: Test again
Once you've completed these steps, retry your php -r one-liner or your command-line mail command:

1. php -r "var_dump(mail('your_email@example.com', 'PHP Test Subject', 'This is a test email sent from PHP via the command line.'));"

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And check your mail logs (/var/log/mail.log or /var/log/maillog) for detailed information about the email delivery.
This systematic approach should help you resolve the "sendmail: not found" error.