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Getting Started with Linux: Novell s Guide to CompTIA s Linux Course 3060

2. Objectives. Understand Processes and JobsView Processes from the GUI and the Command-Line InterfaceManage Jobs and ProcessesUnderstand RunlevelSchedule Tasks. 3. Understand Processes and Jobs. To understand processes and jobs, you need to know the following:Process DefinitionsJobs and Proce

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Getting Started with Linux: Novell s Guide to CompTIA s Linux Course 3060

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    1. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) Section 8 Processes, Jobs, and Runlevels

    2. 2 Objectives Understand Processes and Jobs View Processes from the GUI and the Command-Line Interface Manage Jobs and Processes Understand Runlevel Schedule Tasks

    3. 3 Understand Processes and Jobs To understand processes and jobs, you need to know the following: Process Definitions Jobs and Processes

    4. 4 Process Definitions These terms are used to describe Linux processes: Program: structured set of commands stored in an executable file on a Linux file system Process: program running in memory and on the CPU User process: process launched by a user that runs from a terminal PID: unique ID assigned to every process as it begins Child process: process started by another process Parent process: process that starts other processes PPID: PID of the parent process of current process

    5. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 5 Process Definitions (continued)

    6. 6 Jobs and Processes Each process is identified using a unique PID In Linux, you use a job ID to refer to processes started from an interactive shell In bash, jobs returns all processes that have been started from that shell and run in the background All jobs have a PID, but not all processes have a usable job ID PID 1 always belongs to the init process When the maximum process number has been reached, the next process is allocated the lowest available number (such as PID 7494) After one process has ended, its number again becomes available

    7. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 7 View Processes from the GUI

    8. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 8 View Processes from the Command-Line Interface To view processes, you can use: ps: use to see running processes pstree: displays a list of processes in the form of a tree structure pstree -up | less lsof: use to see which files are opened by processes top: use to find out how much computing time processes use

    9. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 9 View Processes from the Command-Line Interface: ps (continued)

    10. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 10 View Processes from the Command-Line Interface: top

    11. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 11 View Processes from the Command-Line Interface: top (continued)

    12. 12 Control Processes To control processes, you have to know how to: Control Processes Using Signals Prioritize Processes

    13. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 13 Control Processes Using Signals When a process receives a signal it can: Capture the signal and react to it Ignore it if no function exists for handling that signal Processes do not have control over the following signals as they are handled by the kernel: kill -SIGKILL or kill -9 kill -STOP or kill -19 kill 18734 or killall xeyes kill -SIGKILL PID or kill -9 PID For the kernel to forward the signal to a process, it must be sent by the owner of the process or by root

    14. 14 Control Processes Using Signals (continued)

    15. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 15 Exercise 8-1 Control Processes from the GUI and the Command Line If the system seems to react sluggishly, it is helpful to be able to find out the likely cause Various commands available for this purpose, graphical as well as based on the command line The purpose of this exercise is to familiarize you with some of the available tools

    16. 16 Prioritize Processes Linux distributes available computing time equitably NI column in top list contains nice value of process Values: -20 (high) to 19 (low); default is 0 (neutral) Only root can start a process with negative nice value Use renice to change nice value of a running process renice 5 1712 (only root can reduce the nice value)

    17. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 17 Exercise 8-2 Manage Linux Processes and Services Processes can run with different priorities, leaving more (or less) resources for other processes Processes can run in the foreground or in the background, independently from their priority The purpose of this exercise is to show you how you can influence the priorities of different processes

    18. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 18 Understand Runlevel In this objective, you learn the following about runlevels: The init Program The Runlevels init Configuration File (/etc/inittab) init Directories and Scripts

    19. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 19 The init Program The system is initialized by /sbin/init Controls booting up and shutting down of system signal 9 (SIGKILL) has no effect on init Main configuration file is /etc/inittab Determines what happens in the individual runlevels Entries indicate various scripts to be started; scripts are located in /etc/init.d/ (SLES 9) or /etc/rc.d/init.d/ In other distributions, /etc/rc.d/rc.local is run by init after all other initialization is complete Use to add commands for your environment

    20. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 20 The Runlevels (continued)

    21. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 21 The Runlevels (continued) Switch to another runlevel using init: init 3 Useful if you encounter problems caused by a particular service Switch to a lower runlevel to repair the service If GUI freezes, press Ctrl + Alt + Backspace to restart X Or, switch to a text console (Ctrl + Alt + F1), and as root issue init 3 and then init 5 To shutdown or reboot system: init 0 or init 6 It is better to use commands in Table 8-10 shutdown +5 The new hard drive has arrived shutdown -c

    22. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 22 The Runlevels (continued)

    23. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 23 Exercise 8-3 Work with Runlevels There is rarely a reason to change the runlevel The main reason is usually some maintenance work The purpose of this exercise is to teach you how to change runlevels

    24. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 24 init Directories and Scripts (continued)

    25. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 25 Schedule Tasks Most SLES 9 administrators and regular users find that they need to complete certain tasks regularly on a running system (such as updating a database or backing up data) You can automate these jobs in Linux by doing the following: Schedule a Job (cron) Run a Job One Time Only (at)

    26. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 26 Schedule a Job (cron) You can schedule jobs to be run on a regular basis by using the service cron (/usr/sbin/cron) Service checks once a minute to see if jobs have been defined for the current time By default, the service should be activated A crontab file contains the list of jobs A crontab exists for the entire system as well as for each user defined on the system

    27. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 27 System Jobs You control system jobs with the file /etc/crontab The cron jobs that are defined here after installation run the scripts contained in Table 8-12 Do not delete lines from crontab added at installation Jobs are run later if they could not be run at the specified time /var/spool/cron/lastrun/

    28. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 28 User Jobs To allow users to configure cron jobs, use: /var/spool/cron/allow /var/spool/cron/deny By default, contains entries like guest and gast The jobs of a user are in /var/spool/cron/tabs/user These files belong to root Use crontab to edit them

    29. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 29 User Jobs (continued)

    30. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 30 User Jobs (continued) Each line in a file defines a job */10 8-17 * * 1-5 fetchmail mailserver From Monday to Friday, every 10 minutes between 8:00 A.M.-5:00 P.M., “fetchmail mailserver” is run For system jobs, specify the user with permissions to run it, by entering its name between the time details and the name of the command

    31. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 31 Exercise 8-5 Schedule Jobs with cron and at Scheduling jobs with cron is a very common task It can make system administration much easier to have certain regular tasks like backups run automatically outside working hours at is very handy for one-time tasks The purpose of this exercise is for you to use the available tools for scheduling tasks In this exercise, you do the following: Part I: Schedule Jobs with at Part II: Schedule Jobs with cron

    32. 32 Summary Processes are programs executing on the system Every process has a PID, a PPID, and can possibly start an unlimited number of child processes The first process loaded by the kernel is the init, which always has a PID of 1 Background processes have a job ID that you can use to control their execution You can view processes within a desktop environment by using the KDE System Guard, or at a command prompt by using the ps, pstree, lsof, and top commands

    33. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 33 Summary (continued) The KDE System Guard and the kill, killall, and top commands can be used to stop processes by sending them signals You can affect the priority of a process by changing its nice value nice allows user to set the priority of a program and run it A Linux system is categorized using runlevels

    34. Getting Started with Linux: Novell’s Guide to CompTIA’s Linux+ (Course 3060) 34 Summary (continued) The init daemon is responsible for loading and unloading daemons, using the file /etc/inittab /etc/inittab runs scripts that start with S (start) or K (kill) in the /etc/init.d/rc*.d when changing runlevels You can view your current runlevel using the runlevel command, and force the init daemon to change runlevels using the init command Commands may be scheduled to run at a later time using the at daemon To schedule tasks to occur regularly in the future, you must use the cron daemon to create a crontab

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