I’ve recently had to deal with a process leaking file descriptors. The following command came in handy as a quick way to count how many file descriptors a process is using.

Let’s say that we want to count them for the process(es) called firefox:

[bash]ps -ae | grep firefox | perl -lane ‘print $F[0]’ | while read filename; do ls /proc/$filename/fd; done | wc -w[/bash]

TADAA!

here’s a neat little command:

ps -ae | grep <process_name> | perl -lane ‘print $F[0]’ | while read filename; do ls /proc/$filename/fd; done | wc -w

just replace process_name by httpd for example and it’ll tell you how many file descriptions are in use by all the processes with http in them.

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