Today I’m going to write about MySQL replication. Some of the benefits of replication are balancing load, writes and updates can take place on the master, while read operations can take place in the slave and analyzing data on the slave.
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I have been playing around with Nagios lately. This is the most widely used monitoring tool. I’m not going to write another howto, but clarify some things I found missing in the configuration manuals I used.
First you need the PHP module on the apache server for Nagios to work. Else you will find yourself downloading a phtml file to some directory in your box. This is because of the following files in the nagios directory.
xavi@server:~$ sudo find /nagios/ -type f -name "*.php" /nagios/share/side.php /nagios/share/includes/utils.inc.php /nagios/share/main.php /nagios/share/config.inc.php /nagios/share/index.php xavi@server:~$
Another issue I found was the with nrpe plugin. This plugin allows us to run commands on remote hosts. Issue is that default compilation values don’t allow us to pass arguments. To pass arguments from the server to the monitored host it must be compiled with the –enable-command-args argument when compiling the nrpe source. Another thing that must be done is setting the dont_blame_nrpe to 1 in the nrpe.cfg file.
dont_blame_nrpe=1
This changes allows us to run checks with arguments remotely. Example:
server:/nagios/libexec# ./check_nrpe -H 212.34.95.23 -c check_procs -a 100 120 PROCS OK: 96 processes server:/nagios/libexec#
Questions and suggestions are always welcome. 🙂
Todays post is also going to be short.
I have a VPS server running and the other day they had to reboot my host because of maintenance. Things is I lost my running iptables when the box was rebooted. So how do we get this fixed? You can create a script and us update-rc.d and make it run on the default runlevel. However, we are going to do it different. We will use /etc/network/interfaces and iptables-restore.
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This is going to be a really small post. Sometimes there are a lot of comments on files. How do we clean it up a little? Using sed. Lets show an example.
[14:21:55] xavi@NewYork:/tmp $ sed -e '/^#/d' /etc/ssh/sshd_config | sed -e '/^$/d' Port 22 Protocol 2 HostKey /etc/ssh/ssh_host_rsa_key HostKey /etc/ssh/ssh_host_dsa_key UsePrivilegeSeparation yes KeyRegenerationInterval 3600 ServerKeyBits 768 SyslogFacility AUTH LogLevel INFO LoginGraceTime 120 PermitRootLogin yes StrictModes yes RSAAuthentication yes PubkeyAuthentication yes IgnoreRhosts yes RhostsRSAAuthentication no HostbasedAuthentication no PermitEmptyPasswords no ChallengeResponseAuthentication no X11Forwarding yes X11DisplayOffset 10 PrintMotd no PrintLastLog yes TCPKeepAlive yes AcceptEnv LANG LC_* Subsystem sftp /usr/lib/openssh/sftp-server UsePAM yes [14:22:06] xavi@NewYork:/tmp $
First sed removes lines starting with a #. Our input file is the sshd config file, but it can be any other. The output is then piped to remove the empty lines leaving us with a clean configuration file.
Comments are always welcome. Yes, I know there are some security flaws in the config file, but that is not what we are dealing with in this howto. 🙂
References:
Lets explain how to configure Apache MySQL authentication. We will suppose apache web server is already up and running on the server.
First we need to install auth_mysql module.
$ sudo aptitude search libapache2-mod-auth-mysql p libapache2-mod-auth-mysql - Apache 2 module for MySQL authentication $ sudo aptitude install libapache2-mod-auth-mysql