Htop - An Interactive Process Viewer for Linux

Htop is an interactive process viewer and system monitor for Linux that provides a superior alternative to the traditional top command. It offers real-time, color-coded visualization of system resources and running processes with an intuitive interface that allows users to manage processes interactively.

Unlike the static output of top, Htop displays CPU, memory, and swap usage in colorful progress bars at the top of the screen, followed by a scrollable list of processes. This enhanced interface makes system monitoring more efficient and user-friendly for both beginners and experienced administrators.

Installation

Install Htop using your distribution's package manager:

Ubuntu/Debian:

sudo apt install htop

Red Hat/CentOS:

sudo yum install htop

Fedora:

sudo dnf install htop

Launch Htop by typing htop in the terminal.

Interface Overview

The interface displays key process information including:

Key Features and Operations

Process Management

Navigate using arrow keys to select processes. Key operations include:

• Kill Process Press F9 or k to send signals (SIGTERM, SIGKILL, etc.)

• Change Priority Press F7 (increase nice value) or F8 (decrease nice value)

• Tree View Press F5 or t to show parent-child relationships

Filtering and Searching

Htop provides powerful filtering capabilities:

• Filter Press F4 or \ to filter processes by text

• Search Press F3 or / for incremental search

• User Filter Press u to show processes for specific users

Example filtering for bash processes:

[htop 3.2.1] Tasks: 64, 174 thr; 1 running
CPU[|||||||||||             45.2%]
Mem[|||||||||||             1880/7976MB]
Swp[                        0/0MB]

  PID USER     PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
 3091 root      20   0  5488  1660  1280 S  0.0  0.1  0:00.02 bash
 3095 root      20   0  5488  1664  1284 S  0.0  0.1  0:00.01 bash
 3101 user      20   0  5488  1668  1288 S  0.0  0.1  0:00.01 bash

Sorting Options

Press F6 or < to access the sort menu. Available sort criteria include PID, USER, CPU%, MEM%, TIME+, and COMMAND. This helps identify resource-intensive processes quickly.

Tree View Display

The tree view (F5) shows process hierarchies:

[htop 3.2.1] Tasks: 64, 174 thr; 1 running
CPU[|||||||||||             45.2%]
Mem[|||||||||||             1880/7976MB]

  PID USER     PRI  NI  VIRT   RES   SHR S CPU% MEM%   TIME+  Command
    1 root      20   0  10.6M  6080  3984 S  0.0  0.0  0:01.94 /sbin/init
  ?? 123 root   20   0  15.2M  8192  5432 S  0.5  0.1  0:02.15 systemd
  ?? 456 user   20   0  25.4M 12288  8765 S  1.2  0.2  0:05.43 gnome-session

Advanced Features

Customization

Press F2 to access the setup menu for customizing:

• Meter layout and colors

• Column visibility and order

• Display options (detailed CPU time, show program path)

Multi-CPU Display

On multi-core systems, enable detailed CPU view to see per-core usage:

[htop 3.2.1] Tasks: 64, 174 thr; 1 running
CPU0[|||||            11.7%]  CPU1[|||              7.4%]
CPU2[|||||            12.6%]  CPU3[||               4.6%]
Mem[|||||||||||             1880/7976MB]
Swp[                        0/0MB]

System Call Tracing

Press s on a selected process to launch strace for debugging system calls. This feature requires root privileges and the strace utility to be installed.

Conclusion

Htop is an essential tool for Linux system monitoring that surpasses the traditional top command with its interactive interface, real-time updates, and comprehensive process management capabilities. Its ability to filter, sort, and visualize system resources makes it indispensable for troubleshooting performance issues and managing system processes effectively.