Htop

lastmod 2026-01-06created 2018-12-1126 edits

htop is an interactive text-mode process viewer for Unix systems. It aims to be a better top.

This is htop, an interactive process viewer. It requires ncurses. It is developed primarily on Linux, but we also have code for running under FreeBSD and Mac OS X (help and testing are wanted for these platforms!)

This software has evolved considerably over the years, and is reasonably complete, but there is always room for improvement.

Preview

Screenshot-htop.png

Comparison between htop and classic top

In htop you can scroll the list vertically and horizontally to see all processes and full command lines.
In top you are subject to a delay for each unassigned key you press (especially annoying when multi-key escape sequences are triggered by accident).
htop starts faster (top seems to collect data for a while before displaying anything).
In htop you don't need to type the process number to kill a process, in top you do.
In htop you don't need to type the process number or the priority value to renice a process, in top you do.
In htop you can kill multiple processes at once.
top is older, hence, more tested.

Process information

PID: Process ID number of the process
USER: Owner of the process
PR: Priority of the process
NI: The process's nice value, which affects its priority
VIRT: Amount of virtual memory used by the process
RES: Amount of physical RAM used by the process (in kilobytes) - (Resident set size; RSS) - Use this one to calculate memory usage.
SHR: Amount of shared memory used by the process
S: Current state of the process (zombied, sleeping, running, uninterruptedly sleeping, traced)
%CPU: Percentage of time the process has used the processor
%MEM: Percentage of physical RAM used by the process
TIME+: Time the process has used the processor
COMMAND: Name of the command used to start the process

Functions

F1(help): Shows help and what each shortcut key does.
F2(Setup): The htop settings menu.
F3(Search): Search for processes. ( You can also search with the '/' key.)
F4(Filter): Monitor only the processes you want. ( = ps -ef | grep mysqld )
F5(Tree): Shows the parent-child relationships of processes as a tree. Use the + or - key to expand or collapse the tree. ( = same as the pstree command )
F6(Sort): View processes sorted however you want, by CPU, memory, user, etc. ( The field being sorted is highlighted in color, so it is easy to see. )
F7, F8(Nice): Shortcut keys for changing process priority. ( The f7 key raises the priority and the f8 key lowers it. -> That is, the smaller the value, the higher the priority. )
F9(Kill): Shortcut key that terminates a process. ( = kill -9 {PID} ) -> To terminate several processes at once, select multiple processes with the "space" key, then press F9 to terminate them.
F10(quit): Quit htop

Other functions

u: Shows only the processes of a specific user.
i: Changes the I/O priority.
s: Select a process and press the "s" key to show the strace of that process. ( = system call trace (strace) )
l: Select a process and press the "l" key to see the files that process has open.
Typing a number on the htop screen finds the process with that PID.

Columns

List of columns you can see by pressing F2

PID - Process/thread ID
STATE - Process state (S sleeping, R running, D disk, Z zombie, T traced, W paging, I idle)
PPID - Parent process ID
PGRP - Process group ID
SESSION - Process's session ID
TTY_NR - Controlling terminal
TPGID - Process ID of the fg process group of the controlling terminal
MINFLT - Number of minor faults which have not required loading a memory page from disk
CMINFLT - Children processes' minor faults
MAJFLT - Number of major faults which have required loading a memory page from disk
CMAJFLT - Children processes' major faults
UTIME - User CPU time - time the process spent executing in user mode
STIME - System CPU time - time the kernel spent running system calls for this process
CUTIME - Children processes' user CPU time
CSTIME - Children processes' system CPU time
PRIORITY - Kernel's internal priority for the process
NICE - Nice value (the higher the value, the more it lets other processes take priority)
STARTTIME - Time the process was started
PROCESSOR - Id of the CPU the process last executed on
M_VIRT - Total program size in virtual memory
M_RESIDENT - Resident set size, size of the text and data sections, plus stack usage
M_SHARE - Size of the process's shared pages
M_TRS - Size of the text segment of the process
M_DRS - Size of the data segment plus stack usage of the process
M_LRS - The library size of the process (calculated from memory maps)
M_DT - Size of the dirty pages of the process (unused since Linux 2.6; always 0)
ST_UID - User ID of the process owner
PERCENT_CPU - Percentage of the CPU time the process used in the last sampling
PERCENT_MEM - Percentage of the memory the process is using, based on resident memory size
USER - Username of the process owner (or user ID if name cannot be determined)
TIME - Total time the process has spent in user and system time
NLWP - Number of threads in the process
TGID - Thread group ID (i.e. process ID)
PERCENT_NORM_CPU - Normalized percentage of the CPU time the process used in the last sampling (normalized by cpu co
CTID - OpenVZ container ID (a.k.a. virtual environment ID)
VPID - OpenVZ process ID
VXID - VServer process ID
RCHAR - Number of bytes the process has read
WCHAR - Number of bytes the process has written
SYSCR - Number of read(2) syscalls for the process
SYSCW - Number of write(2) syscalls for the process
RBYTES - Bytes of read(2) I/O for the process
WBYTES - Bytes of write(2) I/O for the process
CNCLWB - Bytes of cancelled write(2) I/O
IO_READ_RATE - The I/O rate of read(2) in bytes per second for the process
IO_WRITE_RATE - The I/O rate of write(2) in bytes per second for the process
IO_RATE - Total I/O rate in bytes per second
CGROUP - Which cgroup the process is in
OOM - OOM (Out-of-Memory) killer score
IO_PRIORITY - I/O priority
PERCENT_CPU_DELAY - CPU delay %
PERCENT_IO_DELAY - Block I/O delay %
PERCENT_SWAP_DELAY - Swapin delay %
M_PSS - proportional set size, same as M_RESIDENT but each page is divided by the number of processes sharing it.
M_SWAP - Size of the process's swapped pages
M_PSSWP - shows proportional swap share of this mapping, Unlike "Swap", this does not take into account swapped out
CTXT - Context switches (incremental sum of voluntary_ctxt_switches and nonvoluntary_ctxt_switches)
SECATTR - Security attribute of the process (e.g. SELinux or AppArmor)
COMM - comm string of the process from /proc/[pid]/comm
EXE - Basename of exe of the process from /proc/[pid]/exe
CWD - The current working directory of the process

Calculating memory usage with `/proc/meminfo`

How to calculate system memory usage from / proc / meminfo (e.g. htop)

In htop ...

Total used memory = MemTotal-MemFree
Non cache / buffer memory (green) = Total used memory-(Buffers + Cached memory)
Buffers (blue) = Buffers
Cached memory (yellow) = Cached+ SReclaimable-Shmem
Swap = SwapTotal-SwapFree

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References

Htop_explained_-_peteris.rocks.pdf ↩

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