Just a quick collection of notes on – rather than a definitive guide to – setting up an SSH chroot jail on RHEL 6. The same should work on RHEL 7 and unrelated flavors. For …
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![IMG_1941[1]](https://i0.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/IMG_19411-100x65.jpg "Killing Process Network Access")
![k0c1xg3f9erebub0aeel9842kih-1[1]](https://i2.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/k0c1xg3f9erebub0aeel9842kih-11-100x65.jpg "Installing t CLI power tool for Twitter")
![4bh5tzr851pq7wca4n9e6zus2fn[1]](https://i0.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/4bh5tzr851pq7wca4n9e6zus2fn1-100x65.jpg "Keeping Abreast with Filesystem Changes")
Commands & Shells, Networking »
Adding and Removing sshd instances on CentOS 6
This is a process and a couple of script to allow you to setup an additional sshd service on an alternate port.
The Unix Oriental
Placed quite appropriately in the “Security” category – my favorite Oriental cocktail recipe. Distinguishing it from the classic preparation, are absence of sweet vermouth and lime juice, as well as addition of just a couple …
Notes on ownCloud configuration
The ownCloud file sharing application has been around for some time now, but somehow evaded my attention. My limited imagination makes me say “think of it us Dropbox hosted on the server in your basement”.
Multi-Dimensional Arrays in Bash
Bash does not support multi-dimensional arrays, but there is a way to imitate this functionality, if you absolutely have to.
Asciinema Notes
Asciinema is an awesome tool for recording your console sessions. It’s great for documenting processes and, in general, showing people how shit works: one look is worth a thousand words, as they say. Unfortunately, I …
Late Night Rant: Facebook
According to media reports, since 2012, millions of Facebook and Instagram logins and plaintext passwords have been sitting on some internal Facebook system, accessible by thousands of the company’s employees.
Measure DNS Server Performance
This is not an entirely proper way to benchmark a DNS server, but, in a pinch, it should give you some idea of its responsiveness and stability.
The Facebook Fracas
![gaabtjyr7kjlsqt1dsziphakwvj[1]](https://i0.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/gaabtjyr7kjlsqt1dsziphakwvj1-80x80.jpg "The Facebook Fracas")
The Facebook privacy saga is getting ridiculous. You’re using a free service that you signed up for – nobody was holding a gun to your giant head. And it’s not Gulag either: just delete your profile, uninstall the damned app, and forget Facebook ever existed.
Generating and Running Multiple Scripts
![lqmqmqhf574z485f4ldembi9vtv[1]](https://i1.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/lqmqmqhf574z485f4ldembi9vtv1-80x80.jpg "Generating and Running Multiple Scripts")
Admittedly, this has a limited range of practical applications and is more of a scripting exercise. The command shown here generates a bunch of temporary scripts each containing the sleep command for up to one minute.
Removing Chef Server Installation
Just a quick note on how to completely remove (more or less) Chef server installation from a CentOS/RHEL box.
Auto-Update /etc/hosts
![rkhctxih1a1jdqh7x0cgs00ljh5[1]](https://i1.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/rkhctxih1a1jdqh7x0cgs00ljh51-80x80.png "Auto-Update /etc/hosts")
This was a silly solution to a silly problem, but may come in handy in the future for other things. A user process was establishing frequent connections to a handful of FQDNs. Not having any IP caching capability, every connection attempt was preceded by DNS lookup.
Find Large Folders
When you get a filesystem space alert (and they tend to arrive at 3:37 on Saturday morning), deleting various supersized log files is one option I already covered in adequate detail. That is if you get so lucky as to find such a file to delete…
Deleting Hidden Files
This simplest of problems just never fails to find a new victim. For whatever reason you want to delete all hidden files in the current directory and subfolders. Without much thinking you just type rm …
Quickly Grow tmpfs filesystem
Just a quick command to double the size of the /tmp filesystem that uses tmpfs. This is for those situations when you can’t be bothered to think.
Duck Duck Go Search from Shell
The ddgr python script is a command line interface for Duck Duck Go – a privacy-oriented search engine that, unlike Google, will not give away your data to the likes of Cambridge Analytica. In the …
Obfuscating Shell Scripts
Unix shell scripting language is run by the command-line interpreter and, as such, can be read and understood by anyone with sufficient access and experience. Sometimes this is not a good thing. Sometimes you want …
The Mystery of a Hemisphere
To make this long (and embarrassing) story short: a friend’s kid had a homework assignment in geometry to calculate the surface area of a conjoined cone, a cylinder, and a hemisphere.
Raspbian ‘partitions on different devices’ Error
After downloading a Raspbian image and writing it to an SD card, you get the following error when trying to boot the Pi: “Could not expand filesystem, please try raspi-config or rc_gui. Boot and root …
Tmux Bootstrap Configuration
Just a list of commands to quickly configure tmux with some of the best (i.e. my favorite) plugins and options. Feel free to disagree – you may be right – but I don’t think so.
Find Large Files
Every time a filesystem is running out of space and I need to find something to delete, I end up googling the syntax for the find command to make sure it stays off NFS and …
Show Logged In Users During a Time Window
Let’s say you want to see who was logged in on the server during last weekend. This includes users who, say, logged in on Thursday and haven’t logged out until Saturday afternoon.
Extracting Email Addresses from TCP Streams
Here’s a quick example of using tshark to extract email addresses from TCP streams. Let’s say some application on your server is sending emails and you want to find out who is receiving those emails.
Export WP Posts and Sync to Sharepoint
Long story short: old wiki is overloaded and broken; new wiki is not a wiki but SharePoint – a glorified file server; people are forced to improvise and put documentation on a WP wiki; bosses …
Commands & Shells »
Gnuplot with Bash
OK, so both of these things have been around forever and will be around long after we’re gone. It’s worth your time to learn how to use the to together.
Killing Process Network Access
![IMG_1941[1]](https://i0.wp.com/www.krazyworks.com/wp-content/uploads/2019/01/IMG_19411-80x80.jpg "Killing Process Network Access")
Imagine this scenario: a particular process on your server is connecting to a host outside your internal network and you don’t like that. On the other hand, you can’t just kill that process because you need it.
Applications »
AWS CLI Cheat Sheet
The installation and configuration process for AWS CLI is fairly simple. The package itself is installed with pip (yum -y install python-pip):
Late Night Rant: Agile
CollabNet VersionOne has released it’s 12th annual “State of Agile” report. The survey involved more than 1,400 software professionals in various roles and industries over the fourth quarter of 2017.
Only 12% responded that their organizations …
Data »
Encrypting Log Data During Log Rotation
Most log files do not contain personally-identifiable information or other sensitive data. And even if they do, encryption of all personal data is not mandatory under GDPR. Still, on occasion, for testing and troubleshooting purposes …
File Compression Testing
For some reason I haven’t used zip much on Linux, sticking to the standard tar/gzip combo. But zip seems to be a viable alternative. While not as space-efficient, it is definitely faster; syntax is simple; …
Monitoring »
Automating Web Page Screenshots
Automatic Web page screenshots are commonly used for various monitoring tasks, such as detecting copyright infringement, website defacement, and other legal and security matters. Automatic screenshotting can also be a useful tool for researchers, developers, and journalists. There are free and open-source tools out there that can help you automate the task of creating Web page screenshots.
Automating Web Page Screenshots
Automatic Web page screenshots are commonly used for various monitoring tasks, such as detecting copyright infringement, website defacement, and other legal and security matters. Automatic screenshotting can also be a useful tool for researchers, developers, …
Networking »
Inventory Network Services with Nmap
With the growing number of network-enabled devices in your home, meaningful security becomes elusive. The first step to addressing the situation is knowing what you have. A few examples below use the nmap utility to scan your local network and detect active devices and services.
Verify Network Port Access
There are several tools you can use to verify access to a remote network port: nc, tcping, telnet. Unfortunately, nc from the netcat package has been replaced by the one from nmap, which lacks the -z option, making …
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Igor
Sr. Unix SysAdmin with twenty years experience supporting Solaris, HP-UX, AIX, IRIX, and Linux servers in a large distributed environment.
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