Tutorials Hut

Tutorials Hut

  • Unix For Testers

       Introduction to Unix
       Unix System Architecture
       Unix File System Structure
       Absolute and Relative Path
       Basic Unix Commands
       cal command in Unix
       who command in Unix
       date command in Unix
       clear command in Unix
       more command in Unix
       whoami command in Unix
       uname command in Unix
       man command in Unix
       echo command in Unix
       Unix File System Commands
       ls command in Unix
       cat command in Unix
       cp command in Unix
       mv command in Unix
       pwd command in Unix
       cd command in Unix
       mkdir command in Unix
       rmdir command in Unix
       rm command in Unix
       touch command in Unix
       dirname command in Unix
       tar command in Unix
       Unix Links(ln)
       Hard Link
       Soft Link
       Regular Expressions
        Basic Regular Expressions
       Interval Regular Expressions
       Pipes and Filters
       Unix Text Processing Commands
       cmp command in Unix
       diff command in Unix
       comm command in Unix
       cut command in Unix
       Paste command in Unix
       head command in Unix
       tail command in Unix
       wc command in Unix
       sort command in Unix
       grep command in Unix
       Process Related Command
       top command in Unix
       ps command in Unix
       nice command in Unix
       Kill command in Unix
       nohup command in Unix
       time command in Unix
       File Tranfer Commands in Unix
       file transfer using scp command
       file transfer using rlogin command
       file transfer using telnet command
       ssh(Secure Shell) command in Unix
       ftp file transfer command
       sftp file transfer command
       chmod command in Unix
       File Permission and File Security in Unix



  • Unix Process Commands : ps, nice, kill, nohup, time

    We will learn about processes in Unix and some essential unix process commands that allow us to view ongoing processes in our terminal like ps, jobs and top.

    Below topics are covered in this article:

    What is a Process?

    Any running program or a command given to a system is called a process. A process could run in foreground or background.
    A process is a program in execution.

      • Each process is allocated a process identifier or PID.
      • In general , each process is started by another process, known as parent process.

    Types of processes in Unix

    There are two types of unix process:

    Foreground Processes Unix:

      • It runs on the screen and needs user input, hereafter you have to wait for its completion before being able to enter a new command.
      • It is also referred as interactive process.
      • For example, MS Office power point, Word etc.

    Background Processes Unix:

      • It runs in the background and usually do not need user input. Unlike foreground processes, when a background process has been executed you don’t have to wait for its completion to execute some other command.
      • It is also referred as non-interactive process.
      • For example ,system scanning using antivirus.

    Any command can be run as a background process by typing a space and ‘&’ after the command.

    SYNTAX:
    $ <command> &

    Example for foreground and background process:

    $ ls pwd

    During the execution o above command, no other processes can be run or started as the prompt would not be available.
    Press Ctrl-c which will send a kill signal to any process running in foreground, terminating it immediately or press Ctrl-z to send a suspend signal to any process running in the foreground, pausing it immediately.

    Top command in Unix

    It is used to show all the running processes within the working environment along with their memory and CPU usage.

    Syntax:
    $ top
    Unix Process Commands :Top command in Unix

    Output fields are:

    PID: Unique Process ID given to each process. User: Username of the process owner. PR: Priority given to a process while scheduling. NI: ‘nice’ value of a process. VIRT: Amount of virtual memory used by a process. RES: Amount of physical memory used by a process. SHR: Amount of memory shared with other processes. S: state of the process ‘D’ = uninterruptible sleep ‘R’ = running ‘S’ = sleeping ‘T’ = traced or stopped ‘Z’ = zombie %CPU: Percentage of CPU used by the process. %MEM :Percentage of RAM used by the process. TIME+: Total CPU time consumed by the process. Command: Command used to activate the process.

    ps command in Unix

    ps  stands for ‘Process Status’  and displays information about a selection of the active processes.

    If you want a repetitive update of the selection and the displayed information, use top instead.

      • gives the details about the processes
      • Option –f gives full listing
      • Option –e or –A displays all processes
    To see every process on the system using standard syntax:
              ps -e
              ps -ef
              ps -eF
              ps -ely
    Unix Process Commands: ps

     The output fields are:

    PID :process ID TTY :terminal type TIME: total time the process has been running CMD :name of the command that launches the process

    nice command in Unix

    nice command in unix is used to execute utility or shell script with a particular CPU priority, thus giving the process more or less CPU time than other processes.

    • A niceness of -20 is the highest priority and 19 is the lowest priority.
    • Default value is 0
    • Execute commands with lower priority.
    SYNTAX:
    nice [option] command [arguments]

    You can change the nice value of a process that is already running by using renice command

    SYNTAX:
    renice [value] -p [PID]

    kill command in Unix

    Unix has no stop command instead it has kill command. Kill is used to send a signal to a process. The most commonly used signal is “terminate” (SIGTERM) or “kill” (SIGKILL). However, there are many more.  The full list can be shown with kill -l.

    Unix Process Commands: kill
    • Send signals to processes.
    • The default signal is 15, which is SIGTERM.
    SYNTAX:
    kill -[option] pid

     the process with particular pid will be terminated.

    nohup command in Unix

    Nohup means  no hang up . It is a command  that keep processes running even after exiting the shell or terminal.

      • Continue execution even after logout.
    SYNTAX:
    nohup command [arguments] 

       time command in Unix

    The time command is used to determine how long a given command takes to run. It is useful for testing the performance of your scripts and commands.

      • Displays time usage of a command
        Syntax:
        time [option] [COMMAND]

    for more details refer here

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