I recently received this error while mounting an iso image in a CentOS 5.3 install:

[root@host ~]# mount -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/
ioctl: LOOP_SET_FD: Invalid argument

For more detail:

[root@host ~]# mount -v -t iso9660 -o loop /mnt/glusterfs/ecp-spe-4867.iso /mnt/iso/
mount: going to use the loop device /dev/loop0
ioctl: LOOP_SET_FD: Invalid argument
mount: failed setting up loop device

So what could this mean? The confusing error message “ioctl: LOOP_SET_FD: Invalid argument” means that your ISO image is on a filesystem that is not supported for the loopback device on your system. In my case, that was a GlusterFS mount that was hosting the image.

I copied it into another directory on my root ext3 filesystem and it mounted just fine!

It is easy to do an in-place upgrade of Ubuntu Server from 8.10 ‘Intrepid Ibex‘ to 9.04 ‘Jaunty Jackalope‘. You can do this remotely over ssh or whatever you use to control your server. Best practices say to make sure to backup your server before doing the upgrade. I’ve done several servers this way with no issues!

Issue the command:

sudo apt-get update; sudo apt-get upgrade; sudo apt-get install update-manager-core; sudo do-release-upgrade

Follow any prompts to first upgrade the current distribution with the newest packages, then do the release upgrade.

I recently came across a typo that existed in a bunch of html files on my web server. I thought it should be easy enough to change, but since it was in a number of files, editing it by hand would be time consuming. Fortunately, there is an easy, one liner command to replace the text in multiple files in a sub directory using recursion.

grep -lr -e '<oldword>' * | xargs sed -i 's/<oldword>/<newword>/g'

This command broken down:

• grep for the word in a files, use recursion (to find files in sub directories), and list only file matches
• | xargs passes the results from the grep command to sed
• sed -i uses a regular expression (regex) to evaluate the change: s (search) / search word / target word / g (global replace)

For more information, see man pages for grep, sed, and xarg. Also it is very handy to learn about regular expressions as they are a valuable tool to any command line programmer!

Came across this little maddening issue again today after fixing it a few months back. I created a directory that is password protected using a .htaccess file. However, when trying to access this folder or anything under this directory, a File Not Found 404 error from Wordpress is displayed before it even propts you for the password. The problem here lays within the main Wordpress .htaccess file

The default .htaccess file for WordPress is:

# BEGIN wordpress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END wordpress

This means that if a file is requested from the server, if it is not a file that exists in the server’s folder directory (!-f) and if it is not a directory that exists in the server’s folder directories (!-d) then pass the request onto index.php. This way, Wordpress will handle both customized URLs (such as those used for SEO) and also 404 File Not Found errors.

If you set up a password protected folder in a directory included in a Wordpress install, all of a sudden Wordpress takes over that folder and returns a 404 page, like the file doesn’t exist.

This happens because of a little ‘gotcha’ in the apache configuration. Luckily it is an easy fix.

In the password protected folder’s .htaccess file, you may already have the entries to ask for password access. Before all of that, place the following line:

ErrorDocument 401 /401.html

Then create a 401.html in the main folder, with any text, for example:

PASSWORD PROTECTED FOLDER – Please enter the correct username/password.

Voila, you can now enter your password protected folder again.

There is another workaround this little error, but since it involves editing the main wordpress .htaccess file, it can be overridden during an upgrade.

Solution found on: http://www.webmasterworld.com/apache/3688208.htm

Zabbix is an excellent system monitoring package. It does everything from basic availability checking to detailed system resource analysis. It is capable of graphing the variables pulled from the system, and alerting admins if there is a problem or something needed for attention.

Once you have the Zabbix server set up, you need to install the client on any systems you want to monitor. Windows systems have a precompiled binary to install. On linux, unix or freebsd systems you’ll need to compile binaries. If you have a range of systems that are homogeneous, you can port the binary to those or also compile it with static dependencies. Below are steps to compile, configure and install the zabbix client:

Steps to install a Zabbix Client

1. Download zabbix source code from www.zabbix.com; decompress with ‘tar zxvf’ and cd to directory
2. Configure the make program: ./configure –enable-agent
3. Compile and install the program: make install
4. Add zabbix group and user: groupadd zabbix; adduser -g zabbix -s /sbin/nologin -M -p RANDOMPASS zabbix
5. Create log file: touch /var/log/zabbix_agentd.log; chown zabbix.zabbix /var/log/zabbix_agentd.log
6. Copy init script to /etc/init.d. Scripts are located in ./misc/init.d/ and your distro directory.
7. Make sure bin directory in init script is where Zabbix actually compiled to.
8. chmod 755 /etc/init.d/zabbix_agentd
9. chkconfig zabbix_agentd on
10. Copy agent config script to /etc/zabbix/zabbix_agentd.conf. Current one is:

    # This is config file for zabbix_agentd
    # To get more information about ZABBIX, go http://www.zabbix.com
    
    # This is the ip and port of the main zabbix server
    Server=10.0.0.1
    ServerPort=10051
    Hostname=AGENTHOSTNAME
    ListenPort=10050
    # ListenIP=10.0.0.2
    StartAgents=5
    DisableActive=1
    DebugLevel=1
    PidFile=/var/tmp/zabbix_agentd.pid
    # LogFile=/var/log/zabbix_agentd.log
    LogFileSize=1
    Timeout=10

11. Start the zabbix service: service zabbix_agentd start
12. Open firewall for zabbix port (10050) if necessary.
13. Log into Zabbix on the server, Add server to hosts – use correct templates and groups depending on what type of server it is.
14. Add monitoring and notification as appropriate.
15. Consider if all necessary services are being monitored; test that detection of down services and notifications work properly.