A 20,000円 used LIFEBOOK U939 runs AI coding agents fine

The blogger's earlier project revived a 2010 MacBook Air 11-inch Late 2010 as a CUI-only AI coding terminal running Ubuntu Server, kmscon, uim-fep, Mozc, and tmux. That experiment showed that cloud-based AI inference let even 2GB of RAM work, but also exposed limits: the lack of a GUI terminal scrollback and clipboard, and failures of some agent executables on the old CPU. Those lessons led to a clear shopping list — a relatively recent instruction set, about 8GB of memory, an SSD, smooth Linux support, a usable GUI terminal, light weight, and low price.

The opportunity came with a used Fujitsu LIFEBOOK U938 listed at 15,800 yen, advertised as not supporting the latest Windows Update because of its 7th-generation Core i5-7300U. The blogger planned to install Linux anyway. After Ubuntu MATE 24.04 LTS was installed, the machine ran smoothly, and the blogger ordered a 5,000 yen replacement battery, bringing the total to 20,000 yen.

When the blogger had an AI agent inspect the hardware, the report showed a Core i5-8365U — a 8th-generation, 4-core/8-thread chip — and the chassis label read LIFEBOOK U939. The ordered U938 had a 7th-generation 2-core/4-thread CPU and an upgradeable memory slot (officially up to 12GB), while the U939 has a stronger CPU but soldered 8GB memory. For the stated purpose of running AI coding agents comfortably, the blogger concluded the mix-up was a lucky break, despite the hassle.