RHEL 8 RH124- En CH 8 Monitoring and Managing Linux Processes

TASK_TRACED

A debugging state a process can be placed into. It is also stopped and represented by "T"

Job Control

A feature of the shell which allows a single shell instance to run and manage multiple commands

Background Processes

A group of processes not currently being processed by the controlling terminal, but are waiting. Processes that cannot read input or receive keyboard interrupts. They can write to the terminal

Foreground Processes

A group of processes that are currently being processed by the controlling terminal

Job

A grouping of all processes in the same pipeline and are members of the same process group

Load number

A measurement based on the number of processes in runnable and uninterruptible states. This measurement is taken every 5 seconds, and can be viewed in a report spanning the previous 1, 5, and 15 minutes.

Load average

A measurement provided by the Linux kernel that is a simple way to represent the perceived system load over time.

Core

A possible default action of a signal; Cause a program to save a memory image (core dump), then terminate .

Stop

A possible default action of a signal; cause a program to stop executing (suspend) and wait to continue (resume).

Term

A possible default action of a signal; causes a program to terminate (exit) at once.

New (Child) Process

A process that is created from a parent process.

Process(es)

A running instance(s) of a launched, executable program

TASK_KILLABLE

A sleeping state where a process can exited completely from when a signal is received. Represented by "K", these are used frequently by utilities.

TASK_INTERRUPTABLE

A sleeping state where a process cannot be woken up from a signal. Represented by the "U" flag.

Signal

A software interrupt that is delivered to a process.

Borne Again Shell (BASH) Terminal

A type of interpreter that processes shell commands in linux. This is the interface used to also view the output of commands, such as the ps command.

Process ID (PID)

A unique number assigned at a process for tracking purposes.

Parent Process ID (PPID)

A unique number given to a child process to identify its relationship in a new environment.

Session

An instance of a terminal that can have a foreground process and any number of background processes.

Kill, unblockable (Kill) (Signal 9)

Causes abrupt program termination. Cannot be blocked, ignored, or handled; always fatal.

Keyboard Quit (QUIT) (Signal 3)

Causes program termination. Can be blocked or handled. Sent by pressing INTR key sequence

Terminate (TERM)( Signal 15)

Causes program termination. Unlike SIGKILL, can be blocked, ignored, or handled. The polite way to ask a program to terminate; allows self-cleanup.

lscpu command

Command that displays how many CPU cores the system currently has operational and load average

Environment

Describes the resources in which the process operates. Includes local and global variables, a current scheduling context, and allocated system resources.

aux

Option which displays all processes, including processes without a controlling terminal.

Keyboard Interrupt (INT) (Signal 2)

Re-initialization (configuration reload) without termination.

Parent (Fork) process

Refers to the original process that creates other processes.

Bracketed Processes

Scheduled kernel threads; can be seen with a ps command. E.g. [kthreadd]

Continue (CONT) (Signal 18)

Sent to a process to resume, if stopped. Cannot be blocked . Even if handled, always resumes the process.

lax

Similar to aux, it provides more categories of detail for all processes.

top Command

Similar to lscpu, but contains more advanced options for user configuration.

Stop, Unblockable (STOP) (Signal 19)

Suspends the process. Cannot be blocked or handled.

Process State

The description of what a given process is doing. E.g. running, sleeping, stopped, or zombie

Zombie Resource

The last entry in a process table of a child process when it has finished its fast. The parent process then deletes this reference to free the resource for other tasks.

TASK_STOPPED

The process is paused until resumed. When resumed, the process returns to running state. Represented by "T".

Running state

The status a process that is actively being, or about to be, processed by the CPU. This can be identified by the "R" flag.

Controlling Terminal

The terminal session currently at the focus of the machine.

TASK_REPORT_IDLE

These are used for kernel system processes. These are not counted toward system load. Can accept fatal signals. Represented by "I".

Effective User ID (EUID)

This is usually the current user, this number is used to identify and group processes within the same terminal where the ps command was invoked.

Keyboard stop (TSTP) (Signal 20)

Unlike SIGSTOP, can be blocked, ignored, or handled. Sent by pressing SUSP key sequence (Ctrl+z).

ps command

Used for listing current processes in detail; has different syntax depending on Linux version.

Hangup (HUP) (Signal 1)

Used to report termination of the controlling process of a terminal. Also used to request process

EXIT_DEAD

When the parent cleans up (reaps) the remaining child process structure, the process is now released completely. This state will never be observed in process-listing utilities. Represented by the "X" flag.

Sleeping state

Where a process is waiting for another program or prompt.There are four variants: TASK_INTERRUPTIBLE (S), TASK_UNINTERRUPTIBLE (D), TASK_KILLABLE (K), TASK_REPORT_IDLE (I)

EXIT_ZOMBIE

A child process signals its parent as it exits. All resources except for the process identity (PID) are released. Represented by the "Z" flag.