tag: #linux

Everyone learns SSH keys and stops at authorized_keys. That is exactly the part that does not scale and cannot be revoked cleanly. SSH has had a certificate authority for over a decade that fixes both, kills the host-key TOFU prompt, and gives every login an expiry. Almost nobody uses it. Here is why you should.

A symlink vanishes and the normal logs say nothing. syslog and the journal record what programs choose to say. auditd records what the kernel actually did in the syscall path. That is why it names the culprit, and why it only works if you turned it on first.

Building Linux From Scratch means living without a package manager for the duration, and the absence teaches you what the presence was doing all along. apt install is one command. Underneath it is dependency resolution, ordering, conflict detection, file tracking, and clean removal, all of which you do by hand under LFS, and all of which you stop noticing the moment you have a package manager to do them for you.

The follow-up to running Ubuntu Touch on a Fairphone 4 is the feature that actually distinguishes it from every mainstream phone. Plug the phone into a monitor over USB-C, pair a Bluetooth keyboard, and the phone becomes a desktop computer. The phone's own touchscreen then works as the trackpad. This is convergence, and once it works, it changes what the phone is for.

bcachefs is, on technical merit, the most interesting copy-on-write filesystem to arrive on Linux in a decade. It is also, as of Linux 6.18, no longer in the kernel, ejected after a governance dispute between its author and Linus Torvalds and now shipping as a DKMS module like ZFS. This is the story of a filesystem whose engineering and whose politics point in opposite directions, and what that means for anyone deciding whether to run it.

Plain ip link and ip addr dump a wall of text for every interface, most of it irrelevant when you just want to know what is up and what has an address. The -br flag collapses each interface to a single line, and it is the version you should be reaching for on every troubleshooting call.

shutdown is the command operators reach for out of habit when they want to bring a system down. For the common case (a single-user workstation, a headless server, an ad-hoc maintenance window), halt does the same orderly shutdown with less ceremony and a simpler invocation. The reason shutdown won the muscle memory is historical and no longer applies on modern systemd systems.

On Debian and Ubuntu, two commands look like they do the same thing. They do not. adduser is a Perl wrapper from the adduser package. useradd is the raw binary from upstream shadow-utils. The difference catches operators who write portable scripts and expect either name to work the same way on RHEL or Alpine.

The default Debian installer is competent. It is also opinionated. It makes a dozen choices on your behalf that you would probably make differently if you knew you were making them. The Expert Install is not for elite users. It is for anyone who wants to know what their system actually contains the moment after first boot.

The bash !$ history expansion substitutes the last argument of the previous command which turns destructive operations like rm into a two-step ritual where the first step is always a preview.