Posts Tagged ‘apache 2’

Fix “Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.” in FreeBSD

Monday, May 21st, 2012


I'm running FreeBSD with Apache and PHP on it and I got in dmesg (kernel log), following error:

freebsd# dmesg|grep -i vm.pmap.shpgperproc
Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.

The exact FreeBSD, Apache and php versions I have installed are:

freebsd# uname -a ; httpd -V ; php –version
FreeBSD pcfreak 7.2-RELEASE-p4 FreeBSD 7.2-RELEASE-p4 #0: Fri Oct 2 12:21:39 UTC 2009 i386
Server version: Apache/2.0.64
Server built: Mar 13 2011 23:36:25Server's Module Magic Number: 20050127:14
Server loaded: APR 0.9.19, APR-UTIL 0.9.19
Compiled using: APR 0.9.19, APR-UTIL 0.9.19
Architecture: 32-bit
Server compiled with….
-D APACHE_MPM_DIR="server/mpm/prefork"
-D APR_HAVE_IPV6 (IPv4-mapped addresses enabled)
-D HTTPD_ROOT="/usr/local"
-D SUEXEC_BIN="/usr/local/bin/suexec"
-D DEFAULT_PIDLOG="/var/run/"
-D DEFAULT_SCOREBOARD="logs/apache_runtime_status"
-D DEFAULT_LOCKFILE="/var/run/accept.lock"
-D DEFAULT_ERRORLOG="logs/error_log"
-D AP_TYPES_CONFIG_FILE="etc/apache2/mime.types"
-D SERVER_CONFIG_FILE="etc/apache2/httpd.conf"
PHP 5.3.5 with Suhosin-Patch (cli) (built: Mar 14 2011 00:29:17)
Copyright (c) 1997-2009 The PHP Group
Zend Engine v2.3.0, Copyright (c) 1998-2010 Zend Technologies
with eAccelerator v0.9.6.1, Copyright (c) 2004-2010 eAccelerator, by eAccelerator

After a bunch of research a FreeBSD forums thread , I've found the fix suggested by a guy.

The solution suggested in the forum is to raise up vm.pmap.pv_entry_ma to vm.pmap.pv_entry_max=1743504, however I've noticed this value is read only and cannot be changed on the BSD running kernel;

freebsd# sysctl vm.pmap.pv_entry_max=1743504
sysctl: oid 'vm.pmap.pv_entry_max' is read only

Instead to solve the;

Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
, I had to add in /boot/loader.conf


Adding this values through /boot/loader.conf set them on kernel boot time. I've seen also in the threads the consider increasing either the vm.pmap.shpgperproc is also encountered on FreeBSD hosts running Squid, Dansguardion and other web proxy softwares on busy hosts.

This problems are not likely to happen for people who are running latest FreeBSD releases (>8.3, 9.x), I've read in same above post in newer BSD kernels the vm.pmap is no longer existing in newer kernels.

Secure Apache webserver against basic Denial of Service attacks with mod_evasive on Debian Linux

Wednesday, September 7th, 2011

Secure Apache against basic Denial of Service attacks with mod evasive, how webserver DDoS works

One good module that helps in mitigating, very basic Denial of Service attacks against Apache 1.3.x 2.0.x and 2.2.x webserver is mod_evasive

I’ve noticed however many Apache administrators out there does forget to install it on new Apache installations or even some of them haven’t heard about of it.
Therefore I wrote this small article to create some more awareness of the existence of the anti DoS module and hopefully thorugh it help some of my readers to strengthen their server security.

Here is a description on what exactly mod-evasive module does:

debian:~# apt-cache show libapache2-mod-evasive | grep -i description -A 7

Description: evasive module to minimize HTTP DoS or brute force attacks
mod_evasive is an evasive maneuvers module for Apache to provide some
protection in the event of an HTTP DoS or DDoS attack or brute force attack.
It is also designed to be a detection tool, and can be easily configured to
talk to ipchains, firewalls, routers, and etcetera.
This module only works on Apache 2.x servers

How does mod-evasive anti DoS module works?

Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address which matches the criterias:

  • Requesting the same page more than number of times per second
  • Making more than N (number) of concurrent requests on the same child per second
  • Making requests to Apache during the IP is temporarily blacklisted (in a blocking list – IP blacklist is removed after a time period))

These anti DDoS and DoS attack protection decreases the possibility that Apache gets DoSed by ana amateur DoS attack, however it still opens doors for attacks who has a large bot-nets of zoombie hosts (let’s say 10000) which will simultaneously request a page from the Apache server. The result in a scenario with a infected botnet running a DoS tool in most of the cases will be a quick exhaustion of system resources available (bandwidth, server memory and processor consumption).
Thus mod-evasive just grants a DoS and DDoS security only on a basic, level where someone tries to DoS a webserver with only possessing access to few hosts.
mod-evasive however in many cases mesaure to protect against DoS and does a great job if combined with Apache mod-security module discussed in one of my previous blog posts – Tightening PHP Security on Debian with Apache 2.2 with ModSecurity2
1. Install mod-evasive

Installing mod-evasive on Debian Lenny, Squeeze and even Wheezy is done in identical way straight using apt-get:

deiban:~# apt-get install libapache2-mod-evasive

2. Enable mod-evasive in Apache

debian:~# ln -sf /etc/apache2/mods-available/mod-evasive.load /etc/apache2/mods-enabled/mod-evasive.load

3. Configure the way mod-evasive deals with potential DoS attacks

Open /etc/apache2/apache2.conf, go down to the end of the file and paste inside, below three mod-evasive configuration directives:

<IfModule mod_evasive20.c>
DOSHashTableSize 3097DOS
PageCount 30
DOSSiteCount 40
DOSPageInterval 2
DOSSiteInterval 1
DOSBlockingPeriod 120

In case of the above configuration criterias are matched, mod-evasive instructs Apache to return a 403 (Forbidden by default) error page which will conserve bandwidth and system resources in case of DoS attack attempt, especially if the DoS attack targets multiple requests to let’s say a large downloadable file or a PHP,Perl,Python script which does a lot of computation and thus consumes large portion of server CPU time.

The meaning of the above three mod-evasive config vars are as follows:

DOSHashTableSize 3097 – Increasing the DoSHashTableSize will increase performance of mod-evasive but will consume more server memory, on a busy webserver this value however should be increased
DOSPageCount 30 – Add IP in evasive temporary blacklist if a request for any IP that hits the same page 30 consequential times.
DOSSiteCount 40 – Add IP to be be blacklisted if 40 requests are made to a one and the same URL location in 1 second time
DOSBlockingPeriod 120 – Instructs the time in seconds for which an IP will get blacklisted (e.g. will get returned the 403 foribden page), this settings instructs mod-evasive to block every intruder which matches DOSPageCount 30 or DOSSiteCount 40 for 2 minutes time.
DOSPageInterval 2 – Interval of 2 seconds for which DOSPageCount can be reached.
DOSSiteInterval 1 – Interval of 1 second in which if DOSSiteCount of 40 is matched the matched IP will be blacklisted for configured period of time.

mod-evasive also supports IP whitelisting with its option DOSWhitelist , handy in cases if for example, you should allow access to a single webpage from office env consisting of hundred computers behind a NAT.
Another handy configuration option is the module capability to notify, if a DoS is originating from a number of IP addresses using the option DOSEmailNotify
Using the DOSSystemCommand in relation with iptables, could be configured to filter out any IP addresses which are found to be matching the configured mod-evasive rules.
The module also supports custom logging, if you want to keep track on IPs which are found to be trying a DoS attack against the server place in above shown configuration DOSLogDir “/var/log/apache2/evasive” and create the /var/log/apache2/evasive directory, with:
debian:~# mkdir /var/log/apache2/evasive

I decided not to log mod-evasive DoS IP matches as this will just add some extra load on the server, however in debugging some mistakenly blacklisted IPs logging is sure a must.

4. Restart Apache to load up mod-evasive debian:~# /etc/init.d/apache2 restart

Finally a very good reading which sheds more light on how exactly mod-evasive works and some extra module configuration options are located in the documentation bundled with the deb package to read it, issue:

debian:~# zless /usr/share/doc/libapache2-mod-evasive/README.gz

For the School-examination

Thursday, January 31st, 2008

Tell me which ideotic government would create a site based on php and would make the serverunder Windows?

Just Guess ours the Bulgarian ministry of Science and Knowledge has started a new site dedicated to helping graduating school pupils with the Future School-examinationthey have to make.

It’s pretty easy to see that just observe:

jericho% telnet 80


Connected to
Escape character is ‘^]’.
HEAD / HTTP/1.0HTTP/1.1 200 OK
Connection: close
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Date: Wed, 30 Jan 2008 19:10:18 GMT
Content-Type: text/html; charset=UTF-8Server: Apache/2.2.6 (Win32) PHP/5.2.5X-Powered-By: PHP/5.2.5Set-Cookie: PHPSESSID=fn5jtjbet7clrapi0a5e5kgvt7; path=/
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Keep-Alive: timeout=5, max=100
Connection closed by foreign host.

Just great our Bulgarian government spend money on buying proprietary software OS to run a Free Software based solution.

This example is pretty examplary of what our country looks like. Sad …