Archive for the ‘Linux’ Category

Reset the GroundWork Monitor 6.0 Password

April 9th, 2010 No comments

The GroundWork Monitor is a simple way to deploy Nagios monitoring to networks. It does a great job of monitoring Linux servers, and anything that speaks SNMP.

I recently needed to make some updates to a GroundWork Community Edition VM, and found myself in a situation where the admin user’s dashboard (web browser interface) password had been changed to an unknown value. I was able to SSH into the GroundWork VM though (it’s CentOS Linux based). There’s info floating around the net on how to reset the admin password, but it was written for older versions of GroundWork, so some of the default password, and MySQL schema details have changed.

Here’s what I did to reset the admin user’s password on GroundWork Monitor 6.0 Community Edition:

  • SSH into the GroundWork VM. If you haven’t changed the root user’s default password, then it’s going to be “opensource”
  • Login to MySQL, and run a query to reset the “admin” user’s password to “admin”. The admin password entered below uses a hash:
  • /usr/local/groundwork/mysql/bin/mysql -u root monarch
    update users set password='21232f297a57a5a743894a0e4a801fc3' where user_name='admin';

Updating a Soekris net4511’s BIOS

January 23rd, 2010 No comments

I performed BIOS updates on a stack of Soekris net4511s and net4521s today. Here’s a quick-and-dirty howto for anyone who wants to do the same thing from a Linux host running minicom. Note that these instructions should work on any net45xx series Soekris board, including the net4501.

  1. Download the BIOS update from Soekris’ Downloads Page. As of the time of this writing, if you’re using anything prior to version 1.20 (my Soekris boards were all running 1.15), you’ll want to start with the update to 1.26a, then consider whether you want to upgrade to the latest BIOS from there. Soekris publishes a changelog of their BIOS updates to their website.
  2. Connect your serial port to the Soekris net45xx using a null-modem cable, and use minicom, or your  terminal emulator of choice to establish a connection. Connection settings should be 9600,8,N,1 with hardware and software flow control both turned off.
  3. If your Soekris net45xx’s serial console isn’t already configured to work at 9600bps, you can set this by entering Ctrl-P to enter the Monitor, then set the console speed to 9600bps, and reboot:
    > set ConSpeed=9600
    > reboot
  4. Start up your Soekris box, and enter Ctrl-P when prompted to enter the Monitor. This should bring to you a “>” prompt.
  5. Enter the “download” command, and press Enter.
    > download
  6. In another terminal, run the following command to initiate an xmodem transfer of the updated Soekris BIOS. Substitute in name of the BIOS file:
    # sx -X b4501x_126a.bin > /dev/ttyS0 < /dev/ttyS0
  7. Switch back to your minicom terminal. You should see a “File downloaded succesfully” message. If so, run the following commands to apply the update, and reboot:

That’s it! Your Soekris net4501, net4511 or net4521 should now have an updated BIOS.

Categories: Linux

Directadmin and “Error Parsing Cron File”

October 26th, 2009 No comments

I migrated my web hosting servers from cPanel to Directadmin earlier this year. The transition was smooth for the most part, but one problem was that users with blank crontabs with cPanel had corrupted crontabs post-migration. They could ssh in, and issue crontab -e, but any attempts to manipulate the crontab via Directadmin’s web interface resulted in the following error:

Error Parsing Cron File

The fix for this problem is to clear out all the lines in /usr/local/directadmin/data/users/username/crontab.conf.

Categories: Linux, Web Hosting

Logging into a VMware Server stuck on the “Loading…” Page

August 12th, 2009 No comments

VMware Server is a handy app to run in places where server virtualization is needed, but you can’t justify the expense or effort required to setup a VMware ESXi or Xen host. One of the reoccurring problems that I run into, even on lightly loaded servers is when trying to log into the VMware Infrastructure Web Access interface, the browser gets stuck at “Loading…”, and never brings up the login form. I’ve observed this on Firefox in Linux, Mac OS X and Windows; as well as within Internet Explorer.

It turns out that the fix for this doesn’t involve the browser at all, but rather a VMware Server settings. Some Googling turned up this thread in VMware Communities, which spells out the following fix:

  1. Edit /etc/vmware/webAccess/
  2. Change the following line:proxy.noCache = false…to:

    proxy.noCache = true

  3. Restart the vmware-mgmt service:
    /etc/init.d/vmware-mgmt restart

That’s it! You may need to refresh your browser one more time after this, but after completing these steps, you should now be prompted to login to VMware Infrastructure Web Access.

Categories: Linux, Virtualization

Joining the ACM – A Linux Sysadmin’s Perpective

July 31st, 2009 No comments

The ACM, or the Association of Computing Machinery describes itself as “the world’s largest educational and scientific computing society”. Until recently, I assumed that since I was out of academia, and focused more on things that sysadmins do, like developing, and implementing real-world solutions than the stuff of research papers, the ACM didn’t have much to offer me.

A contributor to this bias was the fact that I joined the ACM a few years ago while I was in college. I was working with a couple professors on a project that involved using Linux virtualization to teach networking concepts. Anyway, the reason I joined the ACM was that I was asked to give a presentation at an academic computing conference. As I recall, the two requirements for being a presenter were having a .edu email address (check), and ACM membership. I quickly signed up, and failed to investigate what benefits ACM membership would bring.

Fast forward to today. I spend a lot of time reading to keep up on current technologies, and while I am able to do most of this online, I still spend a lot of money each year buying books. A significant portion of these are published by O’Reilly, which writes a lot of excellent Linux, Unix, and development books. Cisco Press’ books make up another significant portion of my collection. Most of the networking products that I work with run either Linux or one of the BSDs, but I’m yet to find a publisher that consistently covers such a wide range of networking topics as well as Cisco Press does.

Many of these O’Reilly and Cisco Press books are available online through Safari. I was once a subscriber, and was happy with their service overall, but at $23/month, membership dues added up. This is where ACM membership comes in. For $99/year, they offer a number of benefits, including the one that I was most interested in – access to a large portion (600) of Safari’s collection of books. Restarting my ACM membership seemed like a no-brainer, given that I was about to spend $60 on one of the Cisco Press titles included in the collection.

I just joined, and taking a look at what else the ACM offers members, like what I see:

  • Access to 500 of Books24x7’s books. Looking over the list, I can see that this would be especially useful to those who are more involved in the Microsft and/or management side of things than I am. :) Actually, there are a few Sybex books on that list that look interesting. I’ve been meaning to brush up on my Java and Oracle, and also see a number of books covering those topics. The Linux books on the list include:
    • Ubuntu Linux Bible
    • Professional Linux 10 Programming
    • Setting up LAMP; Getting Linux, Apache, MySQL, and PHP Working Together
    • Linux Firewalls: Attack Detection and Response with iptables, psad, and fwsnort
  • All 184 issues of the Linux Journal. If you’re not familiar with this magazine, it’s an excellent resource covering all things Linux.
  • Element K courses and simulators. I haven’t used these before, but see a course listed for Cisco’s BCMSN exam, which I’m scheduled to take in a few weeks. I’ll check it out.

I feel like I’ve just scratched the service. Even if I don’t find anything else in the membership benefits worth using, $99/year for access to this collection of information is a bargain for a sysadmin who’s serious about learning.

Installing Linux using a serial console

April 3rd, 2009 No comments

Just a quick note on the command to use to start up a RHEL / CentOS 5.x install from the serial console. This can come in handy if you’re using a modem and serial port for out of band management, and the need to conduct a remote reinstall arises. These settings start up a console on ttys0 (Serial Port 1) with the standard 9600/8-N-1 settings.

linux console=ttyS0,9600n8

Categories: Linux

vsftpd's “500 OOPS: cannot change directory” error

March 24th, 2009 No comments

I recently installed a vsftpd FTP server on a CentOS Linux 5.2 box. After changing the FTP user’s home directory, I received the following error message every time I attempted to login as ftp:

500 OOPS: cannot change directory
500 OOPS: child died

Permissions were setup correctly on the ftp user’s home directory, so I did some digging around, and discovered that there’s an SELinux setting that causes this problem. I didn’t want to turn SELinux off, so the solution was to run the following command, which enables access to the ftp user’s home directory.

setsebool -P ftp_home_dir

Categories: Linux

Resuming failed Firefox downloads

March 19th, 2009 No comments

Firefox’s download manager doesn’t have a built-in mechanism for resuming failed downloads. My Internet connection was cut off just long enough this morning for a Firefox download of an ISO image to fail. To resume the download, I used the wget command, which is built into most Linux distributions, and installable if you’re running OS X or Windows. If you’re running Windows you can download wget from GnuWin32. If you’re running OS X, you can install wget with DarwinPorts.

To resume the failed Firefox download, open up a terminal, change to the directory that the is located in, and issue the wget command with the -c option. The -c option tells wget to continue the failed Firefox download. For example:

cd Downloads
wget -c

Categories: Linux

Bypass rm's “argument list too long” error message with xargs

March 2nd, 2009 No comments

When using rm to delete a large number of files, you may come up against a kernel limitation which limits the length of arguments that can be sent to rm:

$ rm *

bash: /bin/rm: Argument list too long

This one-liner utilizes xargs to bypass this limitation:

ls | xargs rm

Categories: Linux

How to reconfigure CPAN

January 23rd, 2009 No comments

I’m always forgetting the command that’s needed to start CPAN’s configuration wizard back up after its initial setup. To reconfigure CPAN, just execute the follow command from the CPAN prompt:

o conf init

Categories: Linux, Scripting