Command Line

The pv command is one that I really enjoy using but it’s also one that I often forget about.

If you offer a web service that users query via scripts or other applications, you’ll probably find that some people will begin to abuse the service.

Diagram: OpenVPN to Rackspace Cloud Servers and Slicehost

On most systems, using Fedora’s preupgrade package is the most reliable way to update to the next Fedora release.

One of the most common questions that I see in my favorite IRC channel is: “How can I secure sshd on my server?

My curiosity is always piqued when I find new ways to manipulate command line output in simple ways.

NOTE: This post is out of date and is relevant only for GlusterFS 2.

It certainly shouldn’t be difficult, but I always have a tough time with OAuth.

Fedora 13 has quite a few changes related to upstart, and one of the biggest ones is how terminals are configured.

When you need to measure network throughput and capacity, I haven’t found a simpler solution than iperf.

Regardless of the type of hosting you’re using - dedicated or cloud - it’s important to take network interface security seriously.

This problem has cropped up for me a few times, but I’ve always forgotten to make a post about it.

About a year ago, I was introduced to the joys of using irssi and screen to access irc servers.

Thanks to a recommendation from [Michael][1] and [Florian][2], I’ve been using [dsh][3] with a lot of success for quite some time.

One of my favorite (and most used) applications on any Linux machine is screen.

Occasionally, I’ll end up with a mailbox full of random data, alerts, or other useless things.

Most linux distributions use some type of mechanism to gracefully stop daemons and unmount storage volumes during a reboot or shutdown.

Just in case some of you out there enjoy nomenclature and theory behind Linux filesystems, here’s some things to keep in mind.

I recently came across a server that was throwing this error into its message log:

By setting a certain bash environment variable, you can limit which commands are kept in the .

Installing new hardware may mean that new kernel need to be loaded when your server boots up.

Using Linux kernel 3.

If your system abruptly loses power, or if a RAID card is beginning to fail, you might see an ominous message like this within your logs:

Apparently, a recent Red Hat Enterprise Linux update for ES3, 4 and 5 caused some Perl applications to throw errors like these:

Create a strong CSR and private key

I’ve struggled at times to get a decent-looking terminal on my desktop, and I believe I’ve found a good one.

A few days ago, I began to install a group of packages with up2date, and the person next to me was surprised that up2date even had this functionality.

In the event that your system is running out of file descriptors, or you simply want to know what your users are doing, you can review their count of open files by running this command:

With RHEL 5 ditching up2date for yum, many Red Hat users might find themselves confused with the new command line flags.

When you create a CSR and private key to obtain an SSL certificate, the private key has some internal data called a modulus.

When you find yourself in a pinch, and you don’t know the limits of a certain Red Hat Enterprise Linux version, you can find this information in one place.

I hear a lot of complaints about Plesk’s backup routines and how they can bring a server to its knees.

If you find yourself in a pinch and you need a temporary fix when your primary IP is blacklisted, use the following iptables rule:

Should you find yourself in the situation where you’ve forgotten the Urchin admin password, don’t worry.

One question I hear quite often is “how do I add IP aliases in FreeBSD?

Add to /etc/make.

With portinstall:

It can be best to upgrade FreeBSD in an offline state, but if you do it online, you can do it like this:

Making Java keystores at the same time as you create a CSR and key is pretty easy, but if you have a pre-made private key that you want to throw into a keystore, it can be difficult.

If you find yourself stuck with over 30,000 files in a directory (text files in this example), packing them into a tar file can be tricky.

One of the main reasons people like passive FTP is that it’s easier to get through firewalls with it.

If you want to get a really basic, wide-open for localhost setup for SNMP, just toss the following into /etc/snmp/snmpd.

If you find that /dev/null is no longer a block device, and it causes issues during init on Red Hat boxes, you will need to follow these steps to return things to normal:

If you find that memory limits differ between root and other users when PHP scripts are run from the command line, there may be an issue with your php.

If you find that someone has done a recursive chmod or chown on a server, don’t fret.

One of the nifty things about FreeBSD’s kernel is that it will limit closed port RST responses, which, in layman’s terms, just means that if someone repeatedly hits a port that’s closed, the kernel won’t respond to all of the requests.

I found myself pretty darned frustrated when my arrow keys didn’t work in iTerm in vi/vim or other ncurses-based applications.

Installing snort from ports on FreeBSD is pretty straightforward, but there are some ‘gotchas’ that you need to be aware of.

If Redhat, CentOS, Fedora, or any other similar OS provides the following error:

If up2date throws some horrible Python errors and rpm says “rpmdb: Lock table is out of available locker entries”, you can restore your system to normality with the following: