Ben's Blog

This assumes that you have postfix installed and running as your SMTP server

First, make sure that you’re root

[bash]whoami[/bash]

I probably shouldn’t have to explain that if you’re reading this but just in case; if that last command returned something else than ‘root’ issue the following command

[bash]sudo su[/bash]

and enter your password

step 1: Let’s install the packages we’re gonna need

[bash]apt-get update
apt-get install spamassassin spamc[/bash]

step 2: Now we configure spamassasin

[bash]cat /etc/default/spamassassin | sed -e ‘s#ENABLED=0#ENABLED=1#g’ > /etc/default/spamassassin
cat /etc/default/spamassassin | sed -e ‘s#CRON=0#CRON=1#g’ > /etc/default/spamassassin
cat /etc/spamassassin/local.cf | set -e ‘s## rewrite_header Subject *****SPAM*****#rewrite_header Subject [*****SPAM*****] > /etc/spamassassin/local.cf[/bash]

and we start/restart it

[bash]/etc/init.d/spamassassin restart[/bash]

step 3: We create a little script that will take desired action upon spamassassin flagging

create a user called spamassassin (or whatever you want as long as you keep it consistent)

[bash]useradd -m spamassassin[/bash]

then edit the script file /home/spamassassin/spamcheck and throw the following in it

[bash] # variables
 
SENDMAIL="/usr/sbin/sendmail -i"
 
EGREP=/bin/egrep
 
SPAMLIMIT=10
 
# exit codes from <sysexits.h>
 
EX_UNAVAILABLE=69
 
# clean up when done or when aborting.
 
trap "rm -f /tmp/out.$$" 0 1 2 3 15
 
# pipe message to spamc
 
cat | /usr/bin/spamc -u spamd > /tmp/out.$$
 
# are there more than $SPAMLIMIT stars in X-Spam-Level header? :
 
if $EGREP -q "^X-Spam-Level: *{$SPAMLIMIT,}" < /tmp/out.$$
 
then
 
# option 1: move spam messages to sideline dir so a human can look at them later:
 
mv /tmp/out.$$ /home/spamassassin/`date +%Y-%m-%d_%R`-$$
 
# option 2: divert spam message to an alternate e-mail address:
 
#$SENDMAIL xyz@xxxx.xx < /tmp/out.$$
 
# option 3: just delete the spam message
 
# rm -f /tmp/out.$$
 
# option 4: still relay the email to the recipient with the subject of the email now containing [*****SPAM*****]
 
# $SENDMAIL "$@" < /tmp/out.$$
 
else
 
$SENDMAIL "$@" < /tmp/out.$$
 
fi
 
# Postfix returns the exit status of the Postfix sendmail command.
 
exit $?[/bash]

make sure that you

[bash]chown spamassassin:spamassassin /home/spamassassin/spamcheck
chmod 750 /home/spamassassin/spamcheck[/bash]

step 4: Ok, so we got spamassassin going and a little script that will take an email and throw it in /home/spamassassin if it’s spam (if you chose option1) now we just need to tell postfix to pass all messages to that script

edit /etc/postfix/master.cf and replace

[code]smtp inet n – – – – smtpd[/code]

with

[code]smtp inet n – n – – smtpd -o content_filter=spamcheck:dummy[/code]

also add the following 2 lines at the bottom of the file (the indentation is important)

[code]spamcheck unix – n n – 10 pipe

flags=Rq user=spamassassin argv=/bin/spamcheck -f ${sender} — ${recipient}[/code]

We’re almost there, just restart postfix and you’re good to go!

[bash]/etc/init.d/postfix restart[/bash]

If you wanna test that out, watch the log while you send emails to your servers

[bash]tail -f /var/log/syslog[/bash]

send a clean mail, make sure that it reaches destination, then send something you know will get flagged as spam and make sure it ends up in /home/spamassasin instead of the intended recipient.

The reason we choose option 1 here is because there’s no point in still relaying a flagged email as it will still clog the recipient’s mailbox. On the other hand we don’t want to just delete it if spamassassin makes a mistake we want to play it safe and keep every emails should something arise, we quarantine the bad ones in /home/spamassassin

Lastly, as long as you have postfix just feeding the emails to a script like we just did, it’s easy to become fancier and do all kinds of processing to the email, on my server I actually call a php script that throws emails in a DB.

If the following happens to you:

[code]apache2: Could not reliably determine the server’s fully qualified domain name, using 127.0.1.1 for ServerName[/code]

just issue a:

[bash]echo Servername `cat /etc/hostname` >> /etc/apache2/apache2.conf[/bash]

Tested on: Ubuntu server 9.04 32b / Ubuntu 12.04 64b

Here’s a neat little command that will let you delete specified files/directories recursively and based on their names.

Let’s do a dry run first to make sure that the command will go through the right files. Run:

[bash]<code class="plain plain">find <directory_to_start_the_recursion_in> -name <file_name</code>>[/bash]

Keep in mind that if you’re gonna have asterisks (*) in the <file_name> you need to escape them like so:

[bash]find /var/www -name *.jpg[/bash]

make sure that the result only lists the files/directories that you indeed want to obliterate. Then improve that last command by adding:

[bash]find <directory_to_start_the_recursion_in> -name <file_name> -exec rm -rf {} ;[/bash]

Since this is a pretty dangerous command even after a dry run, you can use -ok instead of -exec which will prompt you for approval everytime the command it executed.

[bash]find <directory_to_start_the_recursion_in> -name <file_name> -ok rm -rf {} ;[/bash]

This is of course not limited to rm 🙂

Here’s a cool little script that will recursively chmod, giving a permission based on whether it’s dealing with a file or a directory. This is very convenient when you want to add that +x to directories but not files.

[bash]find $1 -type f -exec chmod $2 {} ;
find $1 -type d -exec chmod $3 {} ;[/bash]

Go ahead and edit /usr/bin/chmod_script, copy paste these 2 lines in there, then issue a chmod 755 /usr/bin/chmod_script as root, that’s it!

Usage syntax is as follows:

[bash]chmod_script <directory_to_start_the_recursion_in> <permissions_for_files> <permissions_for+directories>[/bash]

so if I want to use it on /var/www do:

[code]chmod_script /var/www 644 755[/code]

Enjoy!