everything about linux distro and not only
A Linux system under load tells you nothing unless you know where to look. The CPU might be pegged at 100% while memory sits idle, or memory might be exhausted while the CPU waits for disk I/O that never comes. Monitoring is the practice of reading the right signals at the right time, and the…
Cron is the oldest task scheduler still in daily use on Linux systems, and the LFCS exam tests it alongside systemd timers as a distinct scheduling mechanism. The exam objective is explicit: “Schedule tasks to run at a set date and time” and “Verify completion of scheduled jobs” . Cron’s model is simpler than systemd…
Parameter expansion is what turns bash variables from simple placeholders into a real text-processing toolkit. With a single ${…} expression you can extract substrings, provide defaults, replace patterns, strip prefixes and suffixes, and get the length — all without calling external commands like sed, cut, or awk. Key point: Parameter expansion happens inside the shell…
The previous chapter covered CPU and memory monitoring — the resources that determine whether the system is under computational pressure. This chapter covers the other two pillars: disk and network. A system can have idle CPU and plenty of RAM and still be unusable because the disk is full or the network is saturated. These…
The at command is the standard Linux utility for scheduling a command to run exactly once at a specified future time. Unlike cron, which repeats jobs on a schedule, at is designed for one-off tasks: a backup that needs to run in an hour, a reminder that must fire tomorrow morning, or a maintenance script…
Converting strings to uppercase or lowercase comes up constantly — normalizing user input, formatting output, comparing values case-insensitively. Bash gives you four different ways to do it, each with different trade-offs in portability, speed, and readability. Key point: The fastest and cleanest method is bash’s built-in parameter expansion (${var^^} and ${var,,}). The most portable is…
A backup strategy is not a single tool or a single command. It is a plan that answers three questions: what to back up, how often, and how to restore it. The three fundamental backup types — full, incremental, and differential — are the building blocks of that plan. Each one trades storage space, backup…
Access control for scheduled jobs is a deceptively simple topic with a critical distinction: the files that restrict who may create a job are not the same as the files that control whether an existing job runs. For the LFCS exam, this distinction is the difference between answering the objective correctly and creating a false…
Bash arithmetic works in decimal by default, but it can handle octal, hexadecimal, and binary too. Converting between bases is a common task — file permissions, memory addresses, bitmasks, and color codes all use non-decimal bases at some point. Key point: Bash’s arithmetic $((…)) can read numbers in any base using prefixes (0 for octal,…
The previous chapter covered the theory of full, differential, and incremental backups. This chapter puts that theory into practice with the tool that has been the standard for Linux backups since the 1970s: tar. Its name comes from “tape archive” — it was designed for writing backups to magnetic tape — but it is used…