Sendmail Pipe to PHP: Could not open input file

Question

I've installed sendmail and want to pipe incoming emails to php.

Every time I send an email to my server I am getting an email back with an error message:

could not open input file: /root/fw/catcher.php 554 5.3.0 unknown mailer error 1

I think something with the permissions of catcher.php is wrong but I couldn't figure it out by myself.

Sendmail is installed and I have added an alias:

root: "|/usr/bin/php /root/fw/catcher.php"

Permissions (after chmod 777; I tried chmod 777 and chmod 755 but both won't work):

drwxrwxrwx 2 root root 4096 Jul 20 14:27 fw
-rwxrwxrwx 1 root root   45 Jul 20 14:27 catcher.php

catcher.php (converted line endings to Unix style):

#!/usr/bin/php
<?php echo 'Test'; exit(0); ?>

Executing my php file over cli works fine. All of these commands work:

/usr/bin/php /root/fw/catcher.php
/usr/bin/php7.3 /root/fw/catcher.php
php /root/fw/catcher.php
php7.3 /root/fw/catcher.php

I think there is a problem with the permissions of sendmail.

First i would suggest you use a shell script and pass the php file name in that. See this serverfault.com/questions/261191/… and musicalgeometry.com/p/1473 — Tarun Lalwani
– Tarun Lalwani, Commented Jul 22, 2019 at 17:29

Jannes Botis · Accepted Answer · 2019-07-24 13:14:09Z

The error "could not open input file" means that the file cannot be read for some reason.

Please follow these steps to check:

converted line endings to Unix style

I do not know how you check this, but you could try to redo this using dos2unix, as described in this link

dos2unix catcher.php > newcatcher.php

and then compare file sizes.

it could be that BOM breaks the script, as described here, the shebang line "#!/usr/bin/php" tells the system which interpreter needs to be run when invoking such a script.

If the script is encoded in UTF-8, one may be tempted to include a BOM at the beginning. But actually the "#!" characters are not just characters. They are in fact a magic number that happens to be composed out of two ASCII characters. If you put something (like a BOM) before those characters, then the file will look like it had a different magic number and that can lead to problems.

The script will run over cli because you specifically tell it which intepreter to use: php or php7.3:

php /root/fw/catcher.php
php7.3 /root/fw/catcher.php

To remove BOM from the start of the file, try this:

dos2unix catcher.php

Try to run /root/fw/catcher.php, as a shell script without using php or php7.3 executable. From terminal, run:

./root/fw/catcher.php

pgl · Accepted Answer · 2019-07-29 08:50:21Z

0

Have you checked whether SELinux is enabled and enforcing? You can see this with the getenforce command.

If this returns Enforcing, you can fix this in a few ways. You can either disable SELinux enforcement with setenforce Permissive, or create a policy that allows Apache to run sendmail.

To create a policy like this, the easiest way is to use the audit2allow tool, which is part of the policycoreutils-python - so install that if audit2allow isn't available. Then, check /var/log/audit.log to see if there are errors about sendmail not being able to run. These error lines can be piped to audit2allow to create a policy file that can be enabled with semodule -i <module.pp>.

answered Jul 29, 2019 at 8:50

pgl

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