htop — Interactive Process Monitor for the Terminal
Practical guide to htop — monitor, sort, filter and kill processes live in the terminal with the comfortable, colourful top replacement.
htop is an interactive process viewer for the terminal and a comfortable replacement for top: colour-coded CPU and memory meters, mouse support, a tree view and the ability to kill processes with a single keystroke – without typing PIDs. This guide walks you through the command-line options for launching htop and the keys that matter most while it runs, from searching and filtering to sorting and adjusting nice values.
Basic Usage
htop — Start htop in interactive mode.
htophtop -u USER — Show only processes belonging to a specific user.
htop -u www-datahtop -p PID1,PID2 — Monitor specific processes by PID.
htop -p 1234,5678htop -d TENTHS — Set the update delay in tenths of seconds (default: 15 = 1.5s).
htop -d 10htop -t — Start in tree view mode.
htop -thtop -s COLUMN — Sort by a specific column.
htop -s PERCENT_MEMhtop -H — Highlight new and old (changed) processes on startup.
htop -Hhtop -C — Start in monochrome (no color) mode.
htop -CFunction Keys (Bottom Bar)
F1 / h — Help screen.
F2 / S — Setup — configure meters, columns, colors, and display options.
F3 / / — Incremental search by process name.
F4 / \ — Filter processes by name (only matching processes shown).
F5 / t — Toggle tree/forest view.
F6 / > — Sort by a selected column.
F7 — Decrease nice value (increase priority) of selected process.
F8 — Increase nice value (decrease priority) of selected process.
F9 / k — Kill selected process (choose signal from menu).
F10 / q — Quit htop.
Navigation
↑ / ↓ — Move cursor up/down through process list.
← / → — Scroll horizontally to see full command lines.
PgUp / PgDn — Scroll one page up/down.
Home / End — Jump to top/bottom of process list.
Space — Tag/untag a process (for batch operations).
U — Untag all processes.
c — Tag process and its children.
Sorting
P — Sort by CPU usage.
M — Sort by memory usage.
T — Sort by time.
I — Invert sort order.
F6 / > — Open sort column selector.
Display Toggles
H — Toggle user threads display.
K — Toggle kernel threads display.
t / F5 — Toggle tree view.
p — Toggle program path in command column.
m — Toggle merged command display (useful for multi-threaded apps).
e — Show environment variables for selected process.
w — Wrap long command lines.
u — Show only processes of a selected user.
Process Actions
k / F9 — Kill selected process. Shows signal selection menu.
F7 / ] — Decrease nice value (higher priority). Requires root.
F8 / [ — Increase nice value (lower priority).
l — Show open files for selected process (lsof).
s — Show system calls for selected process (strace).
a — Set CPU affinity for selected process.
i — Set I/O priority for selected process (ionice).
Header Meters
CPU bars — Color-coded: blue=low-priority, green=normal, red=kernel, cyan=virtualized, gray=I/O wait.
Memory bar — Color-coded: green=used, blue=buffers, orange/yellow=cache, cyan=ZFS cache.
Swap bar — Red=swap used. Any swap usage may indicate memory pressure.
Load average — 1/5/15 minute averages. Compare against CPU count.
Uptime — System uptime since last boot.
Tasks — Total processes, threads, running, and kernel threads.
Conclusion
htop makes system monitoring fast and tangible: one invocation shows load, memory and processes in real time, and search (/), filter (F4), tree view (F5) and sorting (F6) are all a keystroke away. Be careful with F9/k, though: a kill terminates the selected process immediately, and any unsaved work in a running process is lost – check the target and the signal before you confirm. Your settings (meters, columns, colours) live in ~/.config/htop/htoprc. If htop feels too plain, btop (a modern, more graphical monitor) and the classic top are both worth a look.
Further Reading
- htop – official project site – source, downloads and FAQ for the process monitor
- htop man page – complete reference for options and interactive keys