Quick and dirty fix for VMware Linux guests loosing clock accuracy

I covered on a previous post how to keep the clock synchronized for VMware Linux guest(s). Well this seems to not work at least for recent versions VMware Server 2 (i.e. the one with web based management console). For now the quick& dirty solution I am using is putting a cron job that executes ntpdate pretty often…

My cron job looks like this:

# Temporary fix for the time getting lost
0-59/10 * * * * /usr/sbin/ntpdate north-america.pool.ntp.org > /dev/null 2>1

Yes, this fix requires to have NTPDATE installed (apt-get install ntpdate under Debian).

http_load man page

http_load(1)                                                                                                      http_load(1)

       http_load - multiprocessing http test client

       http_load [-checksum] [-throttle] [-proxy host:port] [-verbose] [-timeout secs] [-sip sip_file] [-cipher str] ( -paral-
       lel N | -rate N [-jitter] ) ( -fetches N | -seconds N ) url_file

       http_load runs multiple http fetches in parallel, to test the throughput of a web server.   However  unlike  most  such
       test clients, it runs in a single process, so it doesn't bog down the client machine.  It can be configured to do https
       fetches as well.

       The -checksum flag tells http_load to do checksums on the files fetched, to make sure they came across ok.  The  check-
       sums  are  computed  the  first  time each URL gets fetched, and then recomputed and compared on each subsequent fetch.
       Without the -checksum flag only the byte count is checked.

       The -throttle flag tells http_load to throttle its consumption of data to 33.6Kbps, to simulate access by modem  users.

       The -proxy flag lets you run http_load through a web proxy.

       The -verbose flag tells http_load to put out progress reports every minute on stderr.

       The -timeout flag specifies how long to wait on idle connections before giving up.  The default is 60 seconds.

       The  -sip  flag  lets you specify a file containing numeric IP addresses (not hostnames), one per line.  These get used
       randomly as the *source* address of connections.  They must be real routable addresses on your  machine,  created  with
       ifconfig, in order for this to work.  The advantage of using this option is you can make one client machine look like a
       whole bank of machines, as far as the server knows.

       The -cipher flag is only available if you have SSL support compiled in.  It specifies a cipher set to use.  By default,
       http_load  will  negotiate  the highest security that the server has available, which is often higher (and slower) than
       typical browsers will negotiate.  An example of a cipher set might be "RC4-MD5" - this  will  run  considerably  faster
       than  the  default.   In addition to specifying a raw cipher string, there are three built-in cipher sets accessible by
         * fastsec - fast security - RC4-MD5
         * highsec - high security - DES-CBC3-SHA
         * paranoid - ultra high security - AES256-SHA
       Of course, not all servers are guaranteed to implement these combinations.

       One start specifier, either -parallel or -rate, is required.  -parallel tells http_load  to  keep  that  many  parallel
       fetches  going  simultaneously.   -rate tells http_load to start that many new connections each second.  If you use the
       -rate start specifier, you can also give the -jitter flag, telling http_load to vary the rate randomly by about 10%.

       One end specifier, either -fetches or -seconds, is required.  -fetches tells http_load to quit when that  many  fetches
       have been completed.  -seconds tells http_load to quit after that many seconds have elapsed.

       The url_file is just a list of URLs, one per line.  The URLs that get fetched are chosen randomly from this file.

       All flags may be abbreviated to a single letter.

       Note  that  while the end specifier is obeyed precisely, the start specifier is only approximate.  If you use the -rate
       flag, http_load will make its best effort to start connections at that rate, but may not succeed.  And if you  use  the
       -parallel flag, http_load will attempt to keep that many simultaneous connections going, but may fail to keep up if the
       server is very fast.

       Sample run:
           % http_load -rate 2 -seconds 300 urls
           591 fetches, 8 max parallel, 5.33606e+06 bytes, in 300 seconds
           9028.87 mean bytes/connection
           1.97 fetches/sec, 17786.9 bytes/sec
           msecs/connect: 28.8932 mean, 44.243 max, 24.488 min
           msecs/first-response: 63.5362 mean, 81.624 max, 57.803 min
           HTTP response codes:
             code 200 -- 591


       Copyright (C) 1998,1999,2001 by Jef Poskanzer .  All rights reserved.

                                                       15 November 2001                                           http_load(1)

How to install MySQL Server on Debian Linux

While installing MySQL Server it is always good to keep in mind that the logs and data folders will potentially have a big size. By default MySQL keeps them in the root mount point (i.e. ‘/’). That may cause your database server system disk to get full, which is never a good idea.

This article describes how to move these two folders to ‘/home’ which is ideally mounted into another disk and has enough space to keep your database data and logs.

First, I install the required apt-get packages as follows:

apt-get update
apt-get install mysql-server

To check the status:

/etc/init.d/mysql status

/usr/bin/mysqladmin  Ver 8.41 Distrib 5.0.51a, for debian-linux-gnu on i486
Copyright (C) 2000-2006 MySQL AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license

Server version          5.0.51a-24
Protocol version        10
Connection              Localhost via UNIX socket
UNIX socket             /var/run/mysqld/mysqld.sock
Uptime:                 3 sec

Threads: 1  Questions: 78  Slow queries: 0  Opens: 23  Flush tables: 1
Open tables: 17  Queries per second avg: 26.000.

Now, stop MySQL, move the folders to the right location, reconfigure MySQL and start again:

# Stop MySQL
/etc/init.d/mysql stop

# Move and reconfigure data
mkdir /home/mysql
mv /var/lib/mysql /home/mysql/mysql-data
ln -s /home/mysql/mysql-data/ /var/lib/mysql

# Move and reconfigure logs
mv /var/log/mysql/ /home/mysql/mysql-logs
ln -s /home/mysql/mysql-logs/ /var/log/mysql

# Start MySQL and check that everything is OK
/etc/init.d/mysql start
/etc/init.d/mysql status
/usr/bin/mysqladmin  Ver 8.41 Distrib 5.0.51a, for debian-linux-gnu on i486
Copyright (C) 2000-2006 MySQL AB
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL license

Server version          5.0.51a-24
Protocol version        10
Connection              Localhost via UNIX socket
UNIX socket             /var/run/mysqld/mysqld.sock
Uptime:                 14 sec

Threads: 1  Questions: 78  Slow queries: 0  Opens: 23  Flush tables: 1
Open tables: 17  Queries per second avg: 5.571.

These are some settings that I usually put on the /etc/mysql/my.cnf configuration file:

# Here you can see queries with especially long duration
log_slow_queries        = /var/log/mysql/mysql-slow.log
long_query_time         = 1

# A server-id unique
server-id                = 177
log-bin                  = /var/log/mysql/mysql-bin.log
log-bin-index            = /var/log/mysql/mysql-bin.log
# Unique log names (this prevents replication breaking upon hostname change :-)
relay-log                = iamalsounique98127-relay-bin
relay-log-index          = iamalsounique98127-relay-bin

# Taking care of the auto-increment values (for multi-master replication)
auto_increment_increment      = 10
auto_increment_offset         = 1

For these changes to take effect, you would need to restart MySQL:

/etc/init.d/mysql restart

If you want to ignore databases or tables you may use the following options:

binlog_ignore_db        = information_schema
replicate_ignore_db     = information_schema
binlog_ignore_db        = mysql
replicate_ignore_db     = mysql

# Ignore all the cache* tables which have caused DUPLICATE
# ENTRY issues. Unai.
replicate_wild_ignore_table = exampledb.cache%

Having ‘binlog_ignore_db’ is enough to exclude databases from replication BUT having ‘replicate_ignore_db’ as well will make things clearer since the databases that are being ignored will appear in both the ‘SHOW SLAVE STATUSG’ and ‘SHOW MASTER STATUSG’.

How to test CAS’ SAML using soapUI

Recent versions (I believe 3.2 or older) of Central Authentication System (a.k.a. CAS) include Security Assertion Markup Language (a.k.a. SAML) support, out of the box. The beauty if it is that it is already “there” accessible through the URL ‘/cas/samlValidate’ instead of the usual ‘/cas/serviceValidate’.

One thing to be noted is that it is not so easy to communicate with your CAS instance using SAML protocol since the requests need to be HTTP POST (which put browsers out of the picture) using a properly formed SAML payload.

Here is when soapUI comes in, which is an excellent tool for web services testing using SOAP requests (there should not be any problem/limitation by using the open source version of the tool) since it can be used to complete the SAML communication and see what the CAS server is actually returning back.

So, in order to complete that, you would need to connect to your CAS server, login by providing valid credentials and then get a CAS ticket. This can be done by opening the following URL on a browser:


The browser should be now displaying an error because it should have been redirected back to the URL http://localhost/foo which probably does not exist. No problem. What is important though is that you would be able to retrieve the ticket from the URL. Example:



Now using SoapUI you need to send CAS a proper SAML request. You may do that using the “submit a request to a specified end point” action. The URL where to send the request should be:

https://CAS_DOMAIN:PORT/cas/samlValidate? ->

the request body should be:


CAS’ response should be similar to this:




The returned username can be found in the ‘NameIdentifier’ tag.

See Also

Note.- special thanks to Juan Huerta, Julien Gribonvald and Marvin Addison for their tips which inspired me to write this post.

How to define shorewall rules to allow VRRP traffic

It is essential for routers that implement the Virtual Router Redundancy Protocol to be able to communicate with each other.

As the protocol defines, the master router needs to send multicast packets to the whole subnet and of course, the rest of the backup routers need to receive this announcements otherwise they will think that the master router is dead and will initiate an election of a master router.

If no router is able to receive this “multicasted” announcements they all will eventually think that they are the only ones alive and thus become master. All of them master. That brings networking issues.

This page covers how to define the rule(s) under shorewall firewall in order to allow this VRRP announcements pass-through.

Rule definition

VRRP’s announcement multicast packets have the following characteristics:

  1. They are sent to the following multicast IP address:
  2. They use the protocol vrrp
  3. They source IP address is a virtual router

Thus, a rule that allows all the incoming VRRP traffic would look like this:

ACCEPT  net fw: vrrp

A rule that allows VRRP packets from a specific router would look like this:



Let’s imagine we have two routers implementing VRRP (using keepalived, for example). Their IPs are: and Their shorewall rules should include the following:


ACCEPT  net: fw: vrrp


ACCEPT  net: fw: vrrp


KeepAlived Installation under Debian Etch

Briefly, KeepAlived is a daemon that is able to provide failover capabilities to servers/services by binding virtual IP addresses to machines. In the event of failure, KeepAlived would reassign this virtual IP to another machine. This action is executed fast (less than 2 seconds) and automatically.

This is a very interesting daemon to be used in combination with HAProxy, for example. It would be possible to have a failovered load balancer. In the event of this load balancer failing, keepalived would switch to another that is up and running in such a clean and fast way that the clients would not notice.

Installation steps under Debian Etch

apt-get update
apt-get install keepalived

The system will ask a couple of questions. I usually reply using the default values, then configure myself manually the daemon, by editing /etc/keepalived/keepalived.conf.

To make the virtual IP address bindable, you should add this line /etc/sysctl.conf:


Check binding:

sysctl -p

net.ipv4.ip_nonlocal_bind = 1

It is convenient to alter the order when keepalived is being started upon restarts. We probably want to have it started at the end so all the services are already running by the time keepalive runs. To do that:

update-rc.d -f keepalived remove
Removing any system startup links for /etc/init.d/keepalived ...

update-rc.d keepalived defaults 90
Adding system startup for /etc/init.d/keepalived ...
/etc/rc0.d/K90keepalived -> ../init.d/keepalived
/etc/rc1.d/K90keepalived -> ../init.d/keepalived
/etc/rc6.d/K90keepalived -> ../init.d/keepalived
/etc/rc2.d/S90keepalived -> ../init.d/keepalived
/etc/rc3.d/S90keepalived -> ../init.d/keepalived
/etc/rc4.d/S90keepalived -> ../init.d/keepalived
/etc/rc5.d/S90keepalived -> ../init.d/keepalived

See Also

Having HAProxy check mysql status through a xinetd script

HAProxy is able to load balance MySQL wonderfully. The main issue is how to make sure that the backend MySQL server to forward the request to is up and running (I mean not just to establish a connection to port 3306, I mean something more “complete”, that performs a little operation against the MySQL server).

It is possible to make haproxy check the status of a mysql server using a small shell script managed through the xinetd daemon.

What this script basically does is performs a basic operation against the mysql database then returns http status 200 if the operation was successful or http status 500 if it there was any error (i.e. mysql was not available).


The script looks like this:

# This script checks if a mysql server is healthy running on localhost. It will
# return:
# "HTTP/1.x 200 OKr" (if mysql is running smoothly)
# - OR -
# "HTTP/1.x 500 Internal Server Errorr" (else)
# The purpose of this script is make haproxy capable of monitoring mysql properly
# Author: Unai Rodriguez
# It is recommended that a low-privileged-mysql user is created to be used by
# this script. Something like this:
# mysql> GRANT SELECT on mysql.* TO 'mysqlchkusr'@'localhost' 
#     -> IDENTIFIED BY '257retfg2uysg218' WITH GRANT OPTION;
# mysql> flush privileges;



# We perform a simple query that should return a few results :-p
/usr/bin/mysql --host=$MYSQL_HOST --port=$MYSQL_PORT --user=$MYSQL_USERNAME 
	--password=$MYSQL_PASSWORD -e"show databases;" > $TMP_FILE 2> $ERR_FILE

# Check the output. If it is not empty then everything is fine and we return
# something. Else, we just do not return anything.
if [ "$(/bin/cat $TMP_FILE)" != "" ]
	# mysql is fine, return http 200
	/bin/echo -e "HTTP/1.1 200 OKrn"
	/bin/echo -e "Content-Type: Content-Type: text/plainrn"
	/bin/echo -e "rn"
	/bin/echo -e "MySQL is running.rn"
	/bin/echo -e "rn"
	# mysql is fine, return http 503
	/bin/echo -e "HTTP/1.1 503 Service Unavailablern"
	/bin/echo -e "Content-Type: Content-Type: text/plainrn"
	/bin/echo -e "rn"
	/bin/echo -e "MySQL is *down*.rn"
	/bin/echo -e "rn"

Steps on the MySQL server

First, you should create the script somewhere, and assign proper permissions:

chown nobody /opt//mysqlchk
chmod   744  /opt//mysqlchk

Then, set permissions into the mysql server:

mysql> GRANT SELECT on mysql.* TO 'mysqlchkusr'@'localhost' 
mysql> flush privileges;
mysql> exit


HTTP/1.x 200 OK

Now, configure xinetd by adding this line at the bottom of /etc/services:

mysqlchk        9200/tcp                        # mysqlchk

Then add this file /etc/xinetd.d/mysqlchk:

# default: on
# description: mysqlchk
service mysqlchk
        flags           = REUSE
        socket_type     = stream
        port            = 9200
        wait            = no
        user            = nobody
        server          = /opt/mysqlchk
        log_on_failure  += USERID
        disable         = no
        only_from       = # recommended to put the IPs that need
                                    # to connect exclusively (security purposes)
        per_source      = UNLIMITED # Recently added (May 20, 2010)
                                    # Prevents the system from complaining
                                    # about having too many connections open from
                                    # the same IP. More info:
                                    # http://www.linuxfocus.org/English/November2000/article175.shtml

Restart xinetd (you can watch for issues on /var/log/syslog):

/etc/init.d/xinetd stop
/etc/init.d/xinetd start


telnet localhost 9200
Connected to localhost.localdomain.
Escape character is '^]'.
HTTP/1.1 200 OK

Content-Type: Content-Type: text/plain

MySQL is running.

Connection closed by foreign host.

Steps on the HAProxy server
Now, in order to make haproxy check the status of the mysql service through the xinetd-managed-script, we should add something similar to this on the haproxy.cfg file:

listen  MySQL
        mode    tcp
	option  httpchk
        server check port 9200 inter 12000 rise 3 fall 3

What is important?

  1. option httpchk.- tells haproxy to check for full http response (i.e. http headers: 2xx OK or 5xx ERROR)
  2. check port XXXX.- tells haproxy to check the status of the service by sending an http request on that port

How to install NAGIOS NRPE plugin under Debian Linux

NRPE allows you to remotely execute Nagios plugins on other Linux/Unix machines. This allows you to monitor remote machine metrics (disk usage, CPU load, etc.). NRPE can also communicate with some of the Windows agent addons, so you can execute scripts and check metrics on remote Windows machines as well. Citation.

You may follow the steps to install NRPE in any of the following ways:

1) Steps (compiling from sources)

First, you should download the latest NRPE version from HERE.

Then, install some required packages:

apt-get update
apt-get install build-essential libssl-dev

Unpack the NRPE addons, configure and install:

cd /opt
tar xvfz nrpe-2.12.tar.gz
cd nrpe-2.12
./configure --enable-command-args
make all
make install-plugin

2) Steps (using apt binaries)

apt-get update
apt-get install nagios-nrpe-plugin

NRPE can now be invoked using the following:


Another option would be to create a symlink to make the invocation easier:

ln -s /usr/lib/nagios/plugins/check_nrpe /usr/bin/check_nrpe



HAProxy hot-reconfiguration

As of version 1.2.8, a new soft-reconfiguration mechanism has been introduced.
It is now possible to “pause” all the proxies by sending a SIGTTOU signal to
the processes. This will disable the listening socket without breaking existing
connections. After that, sending a SIGTTIN signal to those processes enables
the listening sockets again. This is very useful to try to load a new
configuration or even a new version of haproxy without breaking existing
connections. If the load succeeds, then simply send a SIGUSR1 which will make
the previous proxies exit immediately once their sessions are closed ; and if
the load fails, then simply send a SIGTTIN to restore the service immediately.
Please note that the ‘grace’ parameter is ignored for SIGTTOU, as well as for
SIGUSR1 when the process was in the pause mode. Please also note that it would
be useful to save the pidfile before starting a new instance.

The ‘-st’ and ‘-sf’ command line options are used to inform previously running
processes that a configuration is being reloaded. They will receive the SIGTTOU
signal to ask them to temporarily stop listening to the ports so that the new
process can grab them. If anything wrong happens, the new process will send
them a SIGTTIN to tell them to re-listen to the ports and continue their normal
work. Otherwise, it will either ask them to finish (-sf) their work then softly
exit, or immediately terminate (-st), breaking existing sessions. Citation.


The command to be issued to restart HAProxy gracefully would be:

haproxy -f configfile -sf

Example (added the PID location):

haproxy -f /etc/haproxy/haproxy.cfg -p /var/run/haproxy.pid -sf $(cat /var/run/haproxy.pid)