htop – an interactive system-monitor process-viewer

1. htop is an interactive system-monitor process viewer.
2. It’s a utility for process monitoring.
3. It is an alternative to the Linux program top.
4. It displays a frequently updated list of processes running on a system with default ordered by of CPU usage.

Installation and usage:

1. Ubuntu: sudo apt-get install htop
2. MAC: sudo brew install htopAfter installation just run htop in the terminal and it will show a visual interface of process list with many features to interact with those processes.

Features of htop:

1. It uses color to for visual information about processor, swap and memory status etc.
2. Scroll vertically and horizontally so as to view processes with their full commands running.
3. View CPU, Memory, swap usage, total tasks, number of tasks running, Load average, uptime of the system.
4. Displays all individual CPU of the system with respective CPU usage.
5. Select process and scroll process list – Using Up/Down arrow keys.
6. View process list as tree view (.e. process and its subprocesses as tree view) – Using F5 key or ‘t‘ key.
7. Search by process id – Just type the process id and the process will be searched and selected.
8. Search by any name – Using F3 key or ‘/‘ key and then enter the search word to search.
9. Kill a process – Using F9 key or k.
10. Change priority of the process – Using F7 and F8 key. (you’ll have to be root to give anything really high priority that is run htop as root user)
11. Sort process list:
    • by specific column – Using F6 key and selecting the desired column.
    • by CPU% – Using P key
    • by MEM% – Using M key
    • by TIME – Using T key
    • by ascending or descending order for the sorted column – Using F4 key or I key.
12. List open files used by a process – Using l key
13. Trace process system calls: if strace is installed, live update of system calls issued by the process can be viewed – Using the s key.
14. Tag or untag processes for quick reference and view for analyzing – Using space to tag/untag, U to untag all tagged processes.
15. customize the user interface to display/remove information from view, choose a color theme for output, columns need to be displayed for the processes – Using F2 key.
16. View processes of the selected user, hide/show users thread or kernel threads.

Below are the key to be used to interact with processes in htop interface.

Process columns:

1. PID: Process ID of a process.
2. USER: User owning the process.
3. PR: Priority of the process.
4. NI: Nice value for a process to set process priority.
5. VIRT: Virtual memory consumption.
6. RES: Physical RAM consumption in kilobytes.
7. SHR: Shared memory consumption.
8. S: Process status
   • S: sleeping (idle),
   • R: running,
   • D: disk sleep (uninterruptible),
   • Z: zombie (waiting for the parent to read it’s exit status),
   • T: traced or suspended (e.g by SIGTSTP),
   • W: paging
9. CPU%: CPU consumption.
10. MEM%: Physical RAM consumption.
11. TIME+: Processor time used by the process.
12. COMMAND: Command that started the process.

Colour:

1. cpu usage:
   • Blue: low priority processes (nice > 0).
   • Green: normal (user) processes.
   • Red: kernel processes.
   • Yellow: IRQ time.
   • Magenta: Soft IRQ time.
   • Grey: IO Wait time.
2. memory usage:
   • Green: Used memory pages.
   • Blue: Buffer pages.
   • Yellow: Cache pages.

References:

1. http://www.deonsworld.co.za/2012/12/20/understanding-and-using-htop-monitor-system-resources/
2. https://www.ibm.com/developerworks/community/blogs/58e72888-6340-46ac-b488-d31aa4058e9c/entry/montor_linux_processes_in_real_time_through_htop190?lang=en
3. http://linux.die.net/man/1/htop