The Linux Foundation Certified IT Associate (LFCA) is an entry-level certification for people starting careers in IT, cloud, and open-source environments. It covers Linux fundamentals, system administration basics, networking, security essentials, cloud concepts, DevOps principles, and the open-source ecosystem — without requiring prior professional experience. It is vendor-neutral, hands-on oriented, and designed as a foundation for more advanced certifications like the LFCS, CKA, or cloud-specific credentials. Ideal for career changers, students, and junior IT staff who want a broad, practical introduction to modern IT.
The previous chapter covered viewing processes. This chapter covers acting on them. A process that is stuck, a service that is not responding, a runaway job consuming all the CPU, a background task that should be stopped — all of these are managed with signals. A signal is a small message sent to a process,…
A shell is a job controller. It runs commands in the foreground by default — you type a command, it runs, and the prompt returns when it finishes. But a shell can also run commands in the background, suspend a running command, resume it later, and manage a small table of jobs that belong to…
A Linux system is not just a kernel and a shell. It is a collection of long-running programs that start at boot, run in the background, and provide the system’s capabilities: networking, logging, time synchronization, remote access, scheduled tasks, hardware management. These programs are system services — daemons in the traditional Unix vocabulary. A service…
The previous chapter explained what system services are and how systemd defines them. This chapter is about the command that controls them: systemctl. It is the single interface to the init system — starting, stopping, restarting, reloading, enabling, disabling, and inspecting every service on the machine. A service that is not running is started with…
Every service on a systemd system has two independent states, and confusing them is the most common mistake in service management. A service can be running — the process is executing right now — and it can be enabled — it is configured to start when the system boots. These are separate questions with separate…
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…
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…
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…
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…
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…