Free command with examples to viewing memory usage in Linux
Use the free command to inspect total, used, and available memory on a Linux host, with options to format output in human-readable units.
Read moreAbout this section
The Commands category collects command-line guides for everyday Linux administration. Each article walks through a specific utility with practical examples you can run on RHEL, CentOS, Fedora, or other Unix-like systems.
Use these references when you need a quick reminder of syntax, common flags, and expected output for the tools most Linux users reach for first.
Featured command guides
How to check if port is open or in use on Linux or Unix?
Common utilities for verifying whether a TCP or UDP port is listening, in use by a process, or reachable from another host.
Read moreShutdown Linux System from the Command Line
Step-by-step examples for powering off, rebooting, and scheduling shutdowns using the shutdown, poweroff, and systemctl commands.
Read moreHow to change run level in Linux with systemd or init?
Switching between run levels and systemd targets on modern distributions, with examples for both classic init and systemctl.
Read moreHow to set up firewall with firewalld on RHEL/CENTOS 7?
Configuring zones, services, and ports with firewall-cmd to protect RHEL and CentOS 7 servers.
Read moreHow to reset a lost root password in Centos 7 or Redhat 7
Boot into single-user mode and reset the root password when it has been forgotten, with notes on SELinux relabeling.
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