Language Selection

English French German Italian Portuguese Spanish

Custom scripting gives users a safe-du

Filed under

My company has a Linux cluster with a terabyte of attached storage. Over time we noticed the head node was becoming more overloaded. Inspection of the system showed that users were starting dozens of copies of the du utility to determine disk space usage. This was a natural thing for them to do, because they had a need to know how much disk space was available. A lack of disk space would cause their software builds and tests to fail. The problem was that it takes five to seven hours for a du of the entire shared filesystem. Thus, when the filesystem was nearly full (as it of course usually was), the number of du processes would increase almost exponentially.

To address this problem, we first set up automated nightly disk space reports, so that users could check the status without running du. This still did not solve the problem, as the amount of used space could fluctuate dramatically over the course of 24 hours. Users still wanted and needed to run their own du processes throughout the workday.

While adding more disk space would have solved the problem, we are using a large disk array that is already filled to maximum capacity. In general, users tend to fill up all available disk space anyway, no matter how much you give them.

We then developed a policy: users could run du on any directory they owned. In addition, user du processes would be allowed to run for a maximum of one hour of wall time. Users in the wheel group would be exempt from these restrictions.

I was given the task of developing a tool to implement this policy. Some sort of wrapper around the existing du seemed like an obvious choice: the script could validate the input, abort if an invalid path was given, and terminate the du process if it ran too long.

I wrote a basic bash script in perhaps an hour's time. Then I thought about how to run it, and that is where I ran into trouble. I had thought that I would make the script set user id (setuid) or set group id (setgid) root, i.e. when run by any user it would actually run in the root group. Then, I could change the permissions on the real du so that only root could run it. The result would be that normal users could only access the real du through the wrapper script.

Of course that would make a pretty boring article, and in reality it didn't turn out to be that simple:

Full Story.

More in Tux Machines

Fresh Benchmarks Of CentOS 7 On Xeon & EPYC With/Without KPTI/Retpolines

While every few weeks or so we have ended up running benchmarks of the latest Linux Git kernel to see the evolving performance impact of KPTI (Kernel Page Table Isolation) and Retpolines for Meltdown and Spectre V2 mitigation, respectively, a request came in last week from a premium supporter to see some new comparison test runs on CentOS 7 with its older 3.10-evolved kernel. Read more

Reviewing logins on Linux

The last command provides an easy way to review recent logins on a Linux system. It also has some useful options –- such as looking for logins for one particular user or looking for logins in an older wtmp file. The last command with no arguments will easily show you all recent logins. It pulls the information from the current wtmp (/var/log/wtmp) file and shows the logins in reverse sequential order (newest first). Read more

Today in Techrights

Feed the dog and close the door with an open source home automation system

As voice assistants, smart bulbs, and other devices increasingly become household staples, more people than ever are bringing smart technology into their homes. But the bewildering assortment of products on the market can present challenges: Remembering which app to use and trying to link things together with automation can get complicated quickly. In this article, I’ll show you a few ways I used an open source home automation platform, Home Assistant, to bring all my devices together. Read more