How a Path Becomes a File
Path resolution is not a function from strings to strings. The six stages between a pathname and an open file: the trailing slash that defeats O_NOFOLLOW, why .. is a…
The Life of a File Descriptor: Seven Stages from open() to close()
A daemon starts in under a second on one host and takes forty minutes on another — same image, same version, same configuration. No error, no log line, nothing in…
The Life of a Package: Eight Stages Between apt install and Working Software
A server has been running fine for years. A security scanner reports that it is not receiving updates from one of its third-party repositories, nobody can remember it ever failing,…
The Life of a Login: Seven Stages Between a Password and a Shell
A deployment pipeline that has restarted an application over SSH for two years, as the service account that owns it, starts failing the week the hosts are rebuilt onto a…
What Happens When You Type a URL: The Six Stages Before Anything Is Rendered
An internal service is served with a certificate from the company’s own CA. The root was installed on every workstation by configuration management, with the documented command, and update-ca-certificates reported…
DNS, All the Way Down: From getaddrinfo to an Answer
An application on a VPN-connected laptop cannot reach db.internal.corp.example. The operator runs dig @1.1.1.1 db.internal.corp.example, gets NXDOMAIN, and concludes that DNS is broken. The VPN’s resolver has the record and…
Memory, All the Way Down: From malloc to the OOM Killer
Eight stages between a program asking for memory and something being killed for it. Killing is the last one, and almost everything interesting happens before it. This follows a single…
Containers, All the Way Down: What docker run Actually Does
A container is not a kernel object. It is an ordinary process with nine things done to it first. This follows docker run all the way down: the registry request,…
The Shell, in Depth: From Enter to Exit Status
Between pressing Enter and getting your prompt back, the shell rewrites your command line in six stages before anything runs, finds the program four different ways, and puts it in…
The Life of a Write: From write() to the Disk
Your write() call returned successfully and nothing is on the disk. Seven layers sit between that return and durable storage — page cache, filesystem, device mapper, block layer, device cache…