Quasinormal Notes

A Direct Ethernet Link between a MacBook Air and an Arch Linux ThinkPad

A single USB-C to RJ45 cable between a MacBook Air M1 and a ThinkPad P15 running Arch Linux, with fixed addresses, checks of the link, and passwordless SSH for Julia workers and Mathematica kernels.

In this post, we will describe how to connect a MacBook Air M1 to a ThinkPad P15 Gen 1 running Arch Linux with a single Ethernet cable, without using a router or a switch. We will give each machine a fixed address and set up passwordless SSH from the Mac to the ThinkPad. This Ethernet link will connect the two machines (as described in this setup). We will use the Mac to launch Julia workers and Mathematica kernels on the ThinkPad and use both machines concurrently to run our embarrassingly parallel computations. For remote access over the internet, see the notes on remote login, where we have used Tailscale.

Homelab, Guides

The Maltár Tactical Compute Asset

Notes on Maltár, a small cluster I am building from my own laptops, with its first benchmarks in Mathematica and Julia.

I am building a small private compute cluster, Maltár, from machines I already own. It is not meant to replace a workstation or a proper HPC cluster, only to give useful multicore and GPU throughput for physics on hardware that survives the frequent moves and uncertain institutional access of postdoc life.

The cluster has one control node and, once complete, two workers on a private network. Julia and Mathematica jobs are launched from the control node and run in parallel on a shared pool of workers. Maltár is similar to a small heterogeneous Beowulf cluster, but without a job scheduler, since I am its only user.

Homelab, Maltár

Testing Maltár in Julia and Mathematica

Julia and Mathematica code for the first Maltár benchmarks, which time a sweep of Lorenz trajectories and a set of eigenvalue problems on two laptops.

This note gives the code and output of the Phase 1 benchmarks of Maltár, whose results are discussed in Section 5 of the main post. Both benchmarks are run from the MacBook Air M1, with workers started over SSH on the ThinkPad P15, which runs Linux. This needs passwordless SSH login from the MacBook Air to the ThinkPad with a key, Julia at /usr/bin/julia on the ThinkPad with the same packages as on the Mac, and a licensed Mathematica on both machines. For the setup, see the guide to the direct Ethernet link. The code is shown as it was run in the notebooks test_cluster.ipynb and maltar_phase_1.nb, with a few long lines wrapped to fit the page. In the code and its output, minastirith is the hostname of the MacBook Air and isengard that of the ThinkPad.

Homelab, Maltár

The Lore of Maltár

Of Maltár, and of the names of its strongholds, with apologies to J. R. R. Tolkien.

In the great reckoning of the world’s machines there are four orders. At the top stand the vast powers of the age, the Tier-0 engines, like the ancient forges of Valinor, whose might no single mortal can command, and below them lie the Tier-1 realms, the great cities and kingdoms that serve many houses at once. At the bottom stand the lone towers of Tier-3, each a single workstation, powerful but solitary, where the work must stop if ever the hearth goes cold.

Maltár belongs to the middle world, a Tier-2 realm, a small league of strongholds held by a single house and owing nothing to any empire. If one citadel falls, the others still stand and the work goes on, for it is a departmental cluster for a department of one, a wandering scholar who carries his own realm with him.

Yet Maltár is more than a realm, for it is the Hammer of Aulë. Aulë is the smith of Arda, the maker of all things wrought from matter, and his hammer was made for shaping, the instrument by which raw substance becomes form. In the same way Maltár is the force that strikes all its machines into work. The laptops are its anvils and furnaces, and the networks are its bellows, but Maltár itself is the blow that turns silicon into equations and data into knowledge.

Homelab, Maltár

© Subhodeep Vicky Sarkar

The scientist does not study nature because it is useful;
he studies it because he delights in it, and he delights in it because it is beautiful.
~ Henri Poincaré, Science and Method