htop

What it does

htop is an interactive process viewer, similar to top but built for readability and ease of use: it shows colorized per-core CPU meters and a memory/swap bar graph at the top, a scrollable process list below, and supports the mouse for selecting, sorting, and acting on processes. It's not part of core Unix tooling — it's a third-party tool (originally written in C using ncurses) that's become a near-universal install on developer machines and servers because it removes a lot of the friction top has around navigation and process actions.

Beginner examples

• htop — launch the interactive view
• Use arrow keys or the mouse to scroll and select a process
• Press F10 or q to quit
• Press F6 (or </>) to change the sort column, e.g. switch to CPU% or memory%

htop

Advanced examples

• Start already filtered to one user: htop -u alice
• Start in process-tree view to see parent/child relationships immediately: htop -t
• Pin the view to specific PIDs you care about, ignoring everything else: htop -p 1234,5678
• Sort by memory usage from launch instead of the default CPU sort: htop -s PERCENT_MEM
• Run with color disabled, e.g. when logging or piping through a limited terminal: htop -C

htop -u www-data -t

Common mistakes

• Assuming htop is preinstalled everywhere — many minimal server and container images ship only top, so scripts and runbooks that assume htop exists can fail on fresh hosts; install it explicitly (apt install htop / dnf install htop) as a prerequisite.
• Not knowing the function-key shortcuts and trying to type commands like in top — in htop, F9/k kills, F7/F8 renice down/up, and F5/t toggles tree view, mostly navigated by highlighting a row first.
• Confusing the per-core CPU bars at the top with per-process CPU% in the list below — the bars are an aggregate system view, the list rows are per-process.
• Forgetting that, like top, htop's %CPU for a process can exceed 100% on multi-core systems when a process uses more than one core.

Tips

• Press F5 (or t) to toggle tree view — extremely useful for spotting which parent process spawned a runaway child, especially with shell scripts or containerized apps.
• Press F4 to filter the list by typing a search string, narrowing to matching process names live as you type.
• Press Space to "tag" multiple processes, then act on all of them at once (e.g. kill several at a time) instead of one by one.
• Use the mouse to click column headers to sort, or click directly on a process to select it — htop is one of the few classic terminal tools with full mouse support out of the box.

Best practices

• Install htop as part of your standard server provisioning/base image if your team relies on it for triage, rather than discovering it's missing during an incident.
• Use tree view (F5/t) whenever diagnosing a misbehaving service made of multiple processes, so you can see the whole process family rather than a flat, hard-to-relate list.
• Prefer tagging (Space) and batch-acting over repeatedly killing processes one at a time when cleaning up several related runaway processes.
• For non-interactive/scripted contexts (cron jobs, logging), use top -b or ps instead — htop is designed for interactive terminal use, not batch output.

Real-world use cases

• Investigating a server slowdown interactively, using the color-coded CPU/memory bars to spot saturation at a glance before drilling into individual processes.
• Killing a group of orphaned worker processes at once by tagging them with Space and hitting F9, rather than looking up and killing each PID individually.
• Understanding a complex multi-process application's structure (e.g. a web server with worker processes) via tree view to see which processes are children of the main daemon.

Common interview questions

• What are the main differences between htop and top? htop adds color, mouse support, a visual per-core CPU/memory bar graph, an interactive tree view of process hierarchy, and function-key shortcuts for actions like kill/renice — top is more minimal, keyboard-only, and universally preinstalled while htop is a separate package.
• How would you kill several related processes at once in htop? Tag each one with Space, then press F9 (kill) to send a signal to all tagged processes together.
• Is htop guaranteed to be available on every Linux system? No — unlike top, htop is a third-party package not included by default on minimal installs, so it needs to be installed explicitly (e.g. apt install htop).