Les 5

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Les 5 Processes
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Processes inside out

• Multi-user and multi-tasking
• Linux is based on UNIX, where it has been common
  policy to have multiple users running multiple
  commands, at the same time and on the same system

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Daemons

• Daemons are server processes that run
  continuously. Most of the time, they are
  initialized at system startup and then wait in
  the background until their service is required. A
  typical example is the networking daemon, xinetd,
  which is started in almost every boot procedure.
  After the system is booted, the network daemon
  just sits and waits until a client program, such
  as an FTP client, needs to connect

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Job control
regular_command - Runs this command in the
foreground. command - Run this command in the
background (release the terminal) jobs - Show
commands running in the background. CTRLZ -
Suspend (stop, but not quit) a process running in
the foreground (suspend). CTRLC -
Interrupt (terminate and quit) a process running
in the foreground. n - Every process running in
the background gets a number assigned to it. By
using kill - End a process (also see Shell
Builtin Commands in the Info pages of bash)
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Display job information

• Ps
• Top
• Ps axjf (for tree mode)

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Boot proces

• BIOS (POST)
• MBR
• Grub/Lilo
• Init (father of all processes)
• spawns all other processes.
• It runs as a daemon and typically has PID 1.
• /etc/inittab (sets the runlevels)

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Runlevels

• 0 - halt (Do NOT set initdefault to this)
• 1 - Single user mode
• 2 - Multiuser, without NFS (The same as 3, if
  you do not have networking)
• 3 - Full multiuser mode
• 4 - unused
• 5 - X11
• 6 - reboot (Do NOT set initdefault to this)

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Shutdown / reboot

• Shutdown -h now (immediately) or halt
• Shutdown -r now (reboot)
• Reboot
• Init ltrunlevelgt

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Priority

• Nice (-20 (best) to 19 (least))
• Renice (same as nice, but for running procs )

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Scheduling processes

• Use idle time !
• Sleep
• At (The at command executes commands at a given
  time)
• Crontab (easy scheduling)

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Cron and crontab

• The cron system is managed by the cron daemon. It
  gets information about which programs and when
  they should run from the system's and users'
  crontab entries.
• Only the root user has access to the system
  crontabs
• While each user should only have access to his
  own crontabs. On some systems (some) users may
  not have access to the cron facility.

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/etc/crontab
root_at_TBE1ID980168 cat /etc/crontab
/etc/crontab system-wide crontab Unlike any
other crontab you don't have to run the
crontab' command to install the new version
when you edit this file and files in
/etc/cron.d. These files also have username
fields, that none of the other crontabs
do. SHELL/bin/sh PATH/usr/local/sbin/usr/local
/bin/sbin/bin/usr/sbin/usr/bin m h dom mon
dow user command 17 root cd /
run-parts --report /etc/cron.hourly 25 6
root test -x /usr/sbin/anacron ( cd /
run-parts --report /etc/cron.daily ) 47 6
7 root test -x /usr/sbin/anacron ( cd /
run-parts --report /etc/cron.weekly ) 52 6 1
root test -x /usr/sbin/anacron ( cd /
run-parts --report /etc/cron.monthly )
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Crontab usage

• Crontab -l
• Crontab -e
• Kill -HUP ltcron-pidgt (deprecated)

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Summary (1)
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Summary (2)