An IP address is not a single number. It is two: the network the device is on, and the interface’s identity within that network. The split between the two is the subnet, and the way the split is expressed is the CIDR prefix. The subnet determines which destinations are local and which are remote, which…
Every device on a network has an address. The address is how one device finds another, how the packets know where to go, and how the responses find their way back. On the internet and on the local networks that connect to it, that address is the IP address — a number that identifies a…
A filesystem that fills up causes problems: the logs stop being written, the applications fail, the system can behave unpredictably. The two tools for finding out how much space is used are df and du. They answer different questions. df reports the filesystem-level usage — how much of each mounted filesystem is used, how much…
The previous chapter covered the concepts: disks, partitions, filesystems, and the mount model. This chapter covers the commands. Mounting is the act of attaching a filesystem to a directory, and unmounting is the reverse. The mount command does the attaching, umount does the detaching, and findmnt reports the current mount tree. The /etc/fstab file declares…
Storage on Linux is organized in three layers. At the bottom is the disk — a physical device or its virtual equivalent, presented as a block device under /dev. On the disk is a partition table that divides the space into partitions. On each partition is a filesystem that tracks files, directories, permissions, and free…
A signal-based component is a component whose state is expressed with signals, whose inputs are signals, whose outputs are signal-aware, and whose template reads the signals directly. The change detection is driven by the signals, and the component is checked only when the signals it reads change. The model is the modern Angular, and it…
An effect is a function that runs when the signals it reads change. It is the escape hatch from the signal graph to the imperative world — the place where a signal’s change is translated into a side effect that is not a value: a DOM update, a log, a persistence write, an external API…
A computed signal is a derived value. It reads other signals — called its dependencies — and produces a value from them. When any dependency changes, the computed signal marks itself as stale, and the next read recomputes the value. This is the mechanism that turns a set of independent signals into a graph, where…
Signals are Angular’s reactive primitive. A signal is a value that notifies its consumers when it changes, and a component that reads a signal is marked for change detection when the signal changes. The API is small — signal, computed, and effect are the three functions — but the model they implement is the foundation…
State management in Angular has moved through several generations. The first was services holding plain properties, mutated by components. The second was services holding BehaviorSubjects, with components subscribing to the observable streams. The third, in modern Angular, is signals — synchronous, dependency-tracking reactive values. But RxJS has not gone away: signals handle synchronous state, while…