About exim tutorial

Exim is a mail transfer agent (MTA) used on Unix-like operating systems.

To print a list of the messages in the queue:
# exim -bp

To remove all messages from the queue:
# exim -bp | exiqgrep -i | xargs exim -Mrm

Testing email with exim
# exim -v 'user@domain'
# message here
# ^D ( control D )

This will use exim from the command line to create an email message To: user@domain. After typing the message, use Control+D to send the EOF (end of file) characters to exim. Exim will stop receiving input from the command line and send the message text to user@domain.

How to limit the number of emails sent by each user (prevent spammer) with DA.
http://help.directadmin.com/item.php?id=81

Fix Apache – No space left on device: Couldn’t create accept lock

This issue is related to semaphores. To view how many semaphores you have use:

root@hal [~]# sysctl -a | egrep kernel.sem\|kernel.msgmni
kernel.sem = 250 32000 32 128
kernel.msgmni = 16

You can change this values by adding them in /etc/sysctl.conf and then using sysctl -p to activate them.
There is no need to reboot.

To remove sempahores use either one of these commands:

for i in `ipcs -s | grep nobody | awk ‘{print $2}’`; do ipcrm -s $i; done
/scripts/restartsrv_httpd

or in Perl

ipcs -s | grep nobody | perl -e ‘while () { @a=split(/\s+/); print `ipcrm sem $a[1]`}’

or with xargs

ipcs -s | grep nobody | awk ‘ { print $2 } ‘ | xargs ipcrm

or bash style

for ipsemId in $(ipcs -s | grep nobody | cut -f 2 -d ‘ ‘); do ipcrm $ipsemId;done

Other errors :

Cannot create SSLMutex

add in httpd.conf

SSLMutex sem

Nginx + php 5.2.17 + php-fpm

Download the needed packages and store them in /usr/src:

http://us.php.net/distributions/php-5.2.17.tar.gz

http://php-fpm.org/downloads/php-5.2.17-fpm-0.5.14.diff.gz

http://nginx.org/download/nginx-1.1.0.tar.gz

Then run :

tar -xvzf php-5.2.17.tar.gz
gzip -cd php-5.2.17-fpm-0.5.14.diff.gz | sudo patch -d php-5.2.17 -p1
cd php-5.2.17
./configure --enable-fastcgi --enable-fpm --with-mcrypt --with-zlib --enable-mbstring --enable-pdo --with-curl --disable-debug --with-pic --disable-rpath --enable-inline-optimization --with-bz2 --enable-xml --with-zlib --enable-sockets --enable-sysvsem --enable-sysvshm --enable-pcntl --enable-mbregex --with-mhash --with-xsl --enable-zip --with-pcre-regex --with-gd --without-pdo-sqlite --with-pdo-mysql --without-sqlite --with-jpeg-dir=/usr/lib --with-png-dir=/usr/lib --with-mysql --enable-bcmath --enable-calendar --enable-exif --enable-ftp --with-gettext --with-imap --with-mysqli --with-openssl --with-kerberos --with-imap-ssl --enable-dbase --with-gmp --enable-shmop --enable-wddx

make all install

Note that you can add –prefix to install the binaries in a different location than the default one.

After compilation is done :

strip /usr/local/bin/php-cgi
cp sapi/cgi/fpm/php-fpm /etc/init.d/
chmod +x /etc/init.d/php-fpm

cp /usr/src/php-5.2.17/php.ini-recommended /usr/local/lib/php.ini
mkdir /etc/php/
ln -s /usr/local/lib/php.ini /etc/php/php.ini
ln -s /usr/local/etc/php-fpm.conf /etc/php/php-fpm.conf

Make sure you edit /etc/php/php-fpm.conf and set the proper user/group (and permissions if its the case).

Then compile Nginx:

tar zxvf nginx-1.1.0.tar.gz
./configure --sbin-path=/usr/local/sbin --with-http_ssl_module --without-mail_pop3_module --without-mail_imap_module --without-mail_smtp_module --with-http_stub_status_module
make && sudo make install

The same you can modify the –prefix here.

Script to autorestart httpd server if it fails

I use this script on a cpanel server..if output of pgrep command is 0 then the $restart command is issued

#!/bin/bash
restart=”/scripts/restartsrv_httpd”
pgrep httpd || $restart
exit 0

If its a VPS then I might add to clear the Semaphore Arrays.

for i in `ipcs -s | grep nobody | awk ‘{print $2}’`; do ipcrm -s $i; done

Then I put this script into Cron to run every 5 minutes.

# MIN HOUR DAYOFMONTH MONTH DAYOFWEEK COMMAND
*/5 * * * * /root/checkhttp.sh

Monitoring users with last and lastb

Probably all of you know already about the ”last” command and what it outputs.

For example here is what my says:

[aibo@lap ~]$ last | more
giani    pts/2        :0.0             Tue Oct 14 21:45   still logged in
giani    pts/6        :0.0             Tue Oct 14 21:06   still logged in
abo     pts/5        :pts/3:S.1       Tue Oct 14 21:06   still logged in
abo     pts/4        :pts/3:S.0       Tue Oct 14 21:05   still logged in
abo     pts/3        lap.x83.net      Tue Oct 14 21:05   still logged in

It very important to choose strong passwords for all accounts, especially root, since it is the #1 attacked account.

Also an other nice tools is ”’lastb”’ which shows the last failed logins.

Top 5 most recently attacked accounts
[root@lap ~]# lastb | awk '{print $1}' | sort | uniq -c | sort -rn | head -5
      7 root
      2 rancid
      2 giany
      1 btmp
      1

Top 5 most attacked accounts
[root@lap ~]# awk 'gsub(".*sshd.*Failed password for (invalid user )?", "") {print $1}' /var/log/secure* | sort | uniq -c | sort -rn | head -5
    144 root
     30 test
     18 admin
      9 user
      6 webmaster

Top 5 attacker IP addresses
[root@lap ~]# awk 'gsub(".*sshd.*Failed password for (invalid user )?", "") {print $3}' /var/log/secure* | sort | uniq -c | sort -rn | head -5
    397 124.109.44.155
    128 206.169.122.212
    107 89.179.174.40
     24 83.17.92.138
     15 85.25.151.96

Repair a Mysql database

When we try to repair a MySQL database we can stop the service. If you are using the MyISAM engine I recommend using myisamchk. A basic repair sentence could be like this:

myisamchk -r -q -p -v –sort_buffer_size=2000M /var/lib/mysql/database/table.MYI

The used parameters are the following:

* -r recovery mode
* -q quick recovery, the most common one. If this mode does not work you will have to make some research on your own.
* -p creates the keys to be repared in parallel threads.
* -v verbose mode
* –sort_buffer_size= use this to indicate the size of the buffer to sort the keys. If you do not specify this value, or the value you specify is too small, then you will see something like this myisamchk: error: myisam_sort_buffer_size is too small. To solve this just increment the size of the buffer to be used, if the error always appear then you have a extremely big table.