everything about linux distros
Every process on a Linux system leaves a trace. When the kernel boots, it records the hardware it detected and the drivers it loaded. When a user logs in, it notes the time and the source. When a service crashes, it writes the error before dying. These traces are log files, and they are the…
A systemd unit file is not a shell script with a shebang. It is an INI-format configuration file that declares a resource’s metadata, dependencies, execution model, and installation target. The LFCS exam tests this distinction through scenarios that require creating a service from scratch, overriding a package-provided unit without editing the package’s file, and understanding…
Loops are how a script repeats work. Instead of writing the same command ten times, you write it once and let the loop run it ten times. Bash gives you two main conditional loops — while and until — plus for for iterating over lists. This chapter covers while and until; for comes next. Key…
The Linux filesystem has a place for everything. Binaries live in /usr/bin, configuration in /etc, user data in /home, temporary files in /tmp. Logs live in /var/log. This is not an arbitrary choice. The Filesystem Hierarchy Standard reserves /var for variable data — files whose size and content change during normal operation. Logs are the…
Creating a custom systemd unit is the operational bridge between “I have an executable” and “systemd manages this process, restarts it when it crashes, and starts it at boot.” The LFCS exam tests this as a sequence of file creation, section configuration, cache refresh, and enablement—not as a single command. The most common failure is…
When you have one value to check against many possible patterns, a chain of if/elif/else gets ugly fast. The case statement is the cleaner alternative — it matches a value against a list of patterns and runs the first block that matches. Key point: case compares a single value against multiple patterns. Each pattern ends…
The systemd journal is a binary log system that stores messages from the kernel, system services, and applications in a structured format. Unlike text logs that you read with cat or tail, the journal requires a dedicated tool: journalctl. This command is the primary interface for querying systemd logs, and it provides filtering capabilities that…
systemd timers schedule work without cron. The timer unit defines when a job runs, and a paired service unit defines what runs. The two files share a base name: backup.timer triggers backup.service. The exam tests this pairing, the OnCalendar= syntax that replaces cron expressions, the Persistent=true directive that catches missed runs after downtime, and the…
The for loop is the most-used loop in shell scripting. Where while and until repeat until a condition changes, for iterates over a known list of items — numbers, words, files, command output. It’s the loop you reach for when you know what you’re looping over. Key point: Bash gives you five ways to write…
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…