SUSE Linux Enterprise Server Administration Course 3037

1
SUSE Linux Enterprise Server Administration
(Course 3037)

• Chapter 6
• Manage Linux Processes and Services

2
Objectives

• Manage Processes
• Describe Startup Shell Scripts and Services
• Schedule Jobs
• Use System Logging Services

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Manage Processes

• Objectives
• Process Definitions
• Jobs and Processes
• How to Manage Foreground and Background Processes
• How to Prioritize Processes
• How to End a Process
• Processes and Services (Daemons)
• How to Manage a Daemon Process

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Process Definitions

• Program
• Structured set of commands stored in an
  executable file
• Process
• Program that is running in memory and on the CPU
• User process
• Process launched by a user that runs from a
  terminal
• Daemon process
• System process that is not associated with a
  terminal

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Process Definitions (continued)
6
Process Definitions (continued)

• init daemon
• Launches other daemons (daemon processes)
• BASH shell
• Lets user start processes manually (user
  processes)
• Process ID
• Unique identifier assigned to every process
• Child Process
• Process that is started by another process
• Parent Process
• Process that starts other processes
• Parent Process ID (PPID)

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Process Definitions (continued)
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Jobs and Processes

• Job identifier (job ID)
• Shell-specific numeric value that identifies the
  running program
• Used to refer to processes when using commands
• Use job ID to switch a process from background to
  foreground
• Process ID
• Unique across the entire system
• All jobs have a PID
• But not all processes have a usable job
  identifier
• Use PID to change priority level of a running
  program

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How to Manage Foreground and Background Processes

• Processes executed in the foreground
• Started in a terminal window
• Run until the process completes
• Terminal window does not return to a prompt
• Until the programs execution is complete
• Processes executed in the background
• Terminal window returns to a prompt
• Before the process finishes executing
• Processes can be switched from foreground to
  background

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How to Manage Foreground and Background Processes
(continued)

• CtrlZ
• Stops a process running in foreground
• bg
• Continues running a stopped process in the
  background
• Ampersand ()
• Starts the process in the background
• Command jobs
• List the contents of job control

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How to Manage Foreground and Background Processes
(continued)

• fg job_ID
• Switches a process to the foreground
• Process termination status
• Done
• Terminated
• Killed

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How to Prioritize Processes

• ps
• Lists all running processes
• pstree
• Lists processes in the form of a tree structure
• nice
• Assigns a process a specific nice value
• That affects the calculation of the process
  priority
• Nice level is used by the scheduler
• To determine how frequently to service a running
  process

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How to Prioritize Processes (continued)
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How to Prioritize Processes (continued)
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How to Prioritize Processes (continued)
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How to Prioritize Processes (continued)

• renice
• Changes the nice value of a running process
• Only root can reduce nice value of a running
  process
• top
• Combines the functionality of commands ps and
  renice
• Information displayed
• Can be filtered by a specific user
• Can be sorted on any displayed field

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How to Prioritize Processes (continued)
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How to Prioritize Processes (continued)
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How to Prioritize Processes (continued)
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How to End a Process

• kill and killall
• Terminate a process
• killall
• Kills all processes with an indicated command
  name
• Needs the command name of the process
• kill
• Kills only the indicated process
• Needs the PID of the process
• Signals handled by the kernel
• SIGKILL and STOP

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How to End a Process (continued)
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How to End a Process (continued)

• KDE System Guard
• Started from KDE Desktop
• Used to view and kill processes
• Steps
• Select the process from the Process Table
• Select Kill

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How to End a Process (continued)
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Processes and Services (Daemons)

• Service
• Also called a daemon (Disk And Execution MONitor)
• Process or collection of processes
• That wait for an external event to trigger an
  action
• Listener
• Waits for an event to occur and informs the
  program
• Network listeners are common examples

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How to Manage a Daemon Process

• Daemons
• Run in the background
• Usually started when the system is booted
• Terminal-independent processes
• Usually their names terminate in d
• Types of daemons
• Signal-controlled
• Activated when a corresponding task exists
• Interval-controlled
• Activated at certain intervals

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How to Manage a Daemon Process (continued)

• For each daemon, there is a script in
  /etc/init.d/
• For many scripts
• There is a symbolic link in the directory
  /usr/sbin/
• Or in the directory /sbin/
• Some important daemons
• cron
• cupsd
• httpd
• sshd
• syslogd

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How to Manage a Daemon Process (continued)
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Exercise 6-1 Manage Linux Processes and Services

• In this exercise, you do the following
• Part I Move Processes in the Background
• Part II Modify Process Priorities
• Part III Enable Services
• Part IV Enable Services Using YaST

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Describe Startup Shell Scripts and Services

• Objectives
• Startup Scripts
• Startup Script Directory Structure
• Startup Script Structure

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Startup Scripts

• Run as soon as the system is switched to a new
  runlevel
• As long as their dependencies are met
• Scripts for network-based services
• Need to run after the network script is run
• Network script is not run in runlevel 1
• You cannot use network-based services scripts in
  runlevel 1

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Startup Scripts (continued)
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Startup Script Directory Structure

• Directory entries
• /etc/init.d/
• /etc/init.d/rcn.d/
• Link name is prefixed with S (Start) or K (Kill)
• And a two-digit numeric value
• During system startup
• Links with an S in front of them are accessed
• During a clean system shutdown
• Scripts with a K in front of them are accessed

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Startup Script Directory Structure (continued)
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Startup Script Structure

• /etc/init.d/skeleton file
• Skeleton file for startup scripts
• Some of the most important parts include
• General Section
• Start Section
• Stop Section
• Restart Section
• Force-Reload Section
• Reload Section
• Status Section
• Last Option ()

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Startup Script Structure (continued)

• General Section
• Contains commands that are executed regardless of
  the parameter passed to the script
• Start Section
• Parameters are evaluated using a case statement
• Compares the first parameter to the value start
• Stop Section
• Compares the first parameter to the value stop
• And shuts down the process by sending the SIGTERM
  signal

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Startup Script Structure (continued)

• Restart Section
• Used to unconditionally restart the service
• Force-Reload Section
• Commonly used to cause a service to reload its
  configuration files
• Reload Section
• Like the force-reload parameter
• If the service does not support the HUP signal,
  it does nothing

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Startup Script Structure (continued)

• Status Section
• Used to verify the service is running
• Last Option ()
• Used for anything that has not been matched up to
  this point

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Schedule Jobs

• Objectives
• Schedule a Job (cron)
• Run a Job One Time Only (at)

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Schedule a Job (cron)

• Service cron (/usr/sbin/cron)
• Schedules jobs to be carried out on a regular
  basis
• Runs as a daemon
• Checks once a minute for scheduled jobs
• crontab
• File that contains the list of jobs
• Types of jobs
• System Jobs
• User Jobs

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Schedule a Job (cron) (continued)

• System jobs
• Control system jobs with the file /etc/crontab
• /var/spool/cron/lastrun/ directory
• Contains files with information about the last
  time jobs were run
• Script /usr/lib/cron/run-crons
• Evaluates script time stamp
• Determines if scripts have to be run or not
• Scripts in /etc/cron.daily/
• Standard shell scripts
• Overwritten when you update your system

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Schedule a Job (cron) (continued)
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Schedule a Job (cron) (continued)
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Schedule a Job (cron) (continued)

• User jobs
• Configure user cron jobs with the following
  files
• /var/spool/cron/allow
• /var/spool/cron/deny
• Stored in the directory /var/spool/cron/tabs/
• In files matching the user names
• Use crontab to edit them
• Each line in a file defines a job
• There are six fields in a line
• Sixth field contains the command to run

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Schedule a Job (cron) (continued)
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Schedule a Job (cron) (continued)
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Run a Job One Time Only (at)

• Use command at
• Configuration files
• /etc/at.allow
• /etc/at.deny
• at command syntax
• at launch_time (interactive version)
• at f file launch_time

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Run a Job One Time Only (at) (continued)
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Exercise 6-2 Schedule Jobs With cron and at

• In this exercise, you do the following
• Part I Schedule Jobs with at
• Part II Schedule Jobs with cron

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Use System Logging Services

• Objectives
• The syslog Daemon
• Important Log Files
• How to View Log Files with YaST
• How to Archive Log Files (logrotate)
• How to Monitor Hard Drive Space

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The syslog Daemon

• The syslog daemon (syslogd)
• Used by many services to log system events
• Configuration file
• /etc/syslog.conf
• Contains one rule per line
• Each rule has two fields separated by spaces or
  tabs
• Components
• Categories
• Priorities
• Second Field Options
• Additional Priority Parameters

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The syslog Daemon (continued)

• Categories
• Refer to the subsystem that provides the
  corresponding message
• Priorities
• Give details about the urgency of the message
• Second Field Options
• Determine what will be done with the
  corresponding message
• Options
• Output of a file
• Specifying the device file for a text console

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The syslog Daemon (continued)
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The syslog Daemon (continued)
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The syslog Daemon (continued)

• Second Field Options
• Options
• Specifying a FIFO file
• Specifying a user list
• Specifying a computer name with a prefixed _at_
• Using an asterisk ()
• Additional Priority Parameters
• An equal sign () before the priority
• An exclamation mark (!) before the priority
• Add an asterisk ()
• Set none as the priority

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Important Log Files

• /var/log/messages
• Most commonly used log file
• -- MARK -- is written by syslog daemon every 20
  minutes
• If no other messages to log exist
• Command tail
• Used to read log file
• Exit using CtrlC

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Important Log Files (continued)
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Important Log Files (continued)
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How to View Log Files with YaST

• Steps
• Start YaST View Start-up Log or View System Log
  module
• Select a log to view from the drop-down list
• Close the dialog by selecting OK

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How to View Log Files with YaST (continued)
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How to Archive Log Files (logrotate)

• Ensure log files do not get too large or too
  complex
• logrotate program
• Monitors the size and age of log files
• Run daily by the cron daemon
• /etc/cron.daily/logrotate
• /etc/logrotate.conf
• Configuration file of logrotate
• RPM packages contain preconfigured files for
  evaluation by logrotate
• Stored in /etc/logrotate.d/

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How to Archive Log Files (logrotate) (continued)
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How to Archive Log Files (logrotate) (continued)

• Settings in logrotate.d supersede settings in
  logrotate.conf
• syslogd
• Configure how log files written by syslog will be
  treated

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How to Archive Log Files (logrotate) (continued)
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How to Monitor Hard Drive Space

• Command /bin/df (disk free)
• Shows how much space is occupied and available
• Command /usr/bin/du (disk usage)
• Shows how large individual files or directories
  are
• Info Center (Storage Devices) or KDiskFree
• Utilities from the KDE desktop
• Provide a high-level view of disk space usage
• Tree View or Detailed List View in Konqueror
• Monitor disk space usage by directory or file
• Show only individual directory and file sizes

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How to Monitor Hard Drive Space (continued)
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How to Monitor Hard Drive Space (continued)
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How to Monitor Hard Drive Space (continued)
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Exercise 6-3 Manage System Logging

• In this exercise, you do the following
• Part I Modify the Syslog Configuration
• Part II Configure Logrotate

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Summary

• Processes are programs that are executing on the
  system
• Every process has a PID and a PPID
• Can possibly start an unlimited number of child
  processes
• init daemon
• First process loaded by the kernel during system
  initialization
• Background processes have a job ID
• Commands job, bg, fg

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Summary (continued)

• View processes using
• KDE System Guard
• Commands ps, pstree, and top
• Stop processes using
• KDE System Guard
• Commands kill, killall, and top
• Command nice
• Changes process priority
• Daemon process names typically end with d
• Start it with appropriate script in the
  /etc/init.d directory

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Summary (continued)

• init daemon
• Loads daemons during system startup
• Commands may be scheduled to run at a later time
• Using at daemon
• cron daemon
• Used to schedule tasks to occur regularly in the
  future
• Most log files are stored in the /var/log
  directory
• And created by the syslog daemon
• logrotate program is run daily to archive log
  files
• Monitor disk usage with df, du, and KDE utilities