CSE 2234 Introduction to Systems Administration

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CSE 2234 - Introduction to Systems Administration

• Mr. Shawn Stewart
• Computer Sciences

2
CRON (Ch. 9)

• What is cron?
• cron is a daemon that is used to execute jobs at
  specific times or regular intervals.
• Configuration file is called crontab.
• Usually kept in /var/spool/cron
• Editable only with the crontab command
• Format.
• One entry per line
• 1st block is Minute hour day month weekday(0-7)
• 2nd block is command line with the full-path of
  program
• Note that this command must be in bourne-shell
  syntax(sh)

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AT?

• at is a function of cron that allows a one-time
  job to be scheduled in the future
• Simply run
• at -t CCYYMMDDhhmm.SS command
• Again it must be sh compatable syntax

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CRONTAB

• crontab has a couple of options
• crontab -e will open your crontab for editing
  in whatever editor is specified in the EDITOR
  env. Variable
• crontab -l will display your current cron
• crontab -r will remove it.
• root can append a username to the command to
  operate on any users cron.

5
Daemons/Services (Ch. 28)

• What is a daemon?
• Any process that runs w/o a real user
• Why do we need them?

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Common Daemons

• init.d
• inet.d
• cron
• swapper/kswapd
• pageout/pagedaemon/pager
• lpd
• nfsd
• .

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init.d

• This is the master daemon.
• It is one of the first programs run _at_ startup
• It determines run-levels and thus controls when
  startup scripts are executed.
• It also forks off all other processes making it
  the absolute parent

8
inet.d

• This program is used to listen to various network
  sockets for incoming connections and when hit
  forks off the appropriate program and passes off
  the socket
• How is this good/bad?

9
pageout/pagedaemon/

• This program manages what/when/how memory pages
  are swapped to disk.

10
swapper/kswapd/

• This daemon monitors the number of page-faults in
  relation to number of memory refs.
• If there are large sequence of faults called,
  program is repeatedly calling same memory, this
  daemon will swap out entire processes to avoid
  thrashing.

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Others

• lp.d
• One of many network priting daemons.
• nfs.d
• One of 3 NFS-related daemons.
• Moresee Chapter 28

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Quiz

• Please go to
• http//www.cs.fit.edu/Academics/moodle/mod/quiz/vi
  ew.php?id327

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Next week

• MidTerm One - Covering Chapters
• 1, 2
• 12, 3, 6
• 4, 5, 8
• 9, 28