Controlling%20Processes%20

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Controlling Processes Periodic Processes

• WeeSan Lee ltweesan_at_cs.ucr.edugt
• http//www.cs.ucr.edu/weesan/cs183/

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Roadmap

• What is a process?
• What is a setuid process?
• How to create a process?
• Signals
• How to send signals to the processes?
• Process States
• Niceness
• Monitor Processes
• Periodic Processes
• QA

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What is a process?

• A running program
• Information of a process
• PID
• PPID
• UID EUID (used for access permission)
• GID EGID (used for access permission)
• Status
• Niceness or nice value

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What is a setuid process?

• A regular process
• EUID UID of the user who runs the
  command/script
• A setuid process
• EUID the owner UID of the setuid
  command/script
• How to find setuid programs?
• find /bin -perm -4000 xargs ls -l
• -rwsr-xr-x 1 root root 57908 Nov 30 1435
  /bin/mount
• -rwsr-xr-x 1 root root 35864 Mar 14 2007
  /bin/ping
• -rwsr-xr-x 1 root root 31244 Mar 14 2007
  /bin/ping6
• -rwsr-xr-x 1 root root 24060 Mar 21 2007 /bin/su
• -rwsr-xr-x 1 root root 38840 Nov 30 1435
  /bin/umount

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How to create a process?

• emacs

// Bash clone switch (fork()) case -1 //
Error break case 0 // Child
execv("emacs", ) break default // Parent
wait() break
// Bash switch (fork()) case -1 // Error
break case 0 // Child execv("emacs", ...)
break default // Parent wait() break
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Signals

• Process-level interrupt requests
• 30 signals
• kill -l
• Can be caught or trapped by a process
• In Bash, we do
• trap done2() exit 0 1 2 3 15
• Can be blocked or ignored

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Signals (cont)

• Common signals
• 1 HUP
• 2 INT
• Ctrl-C
• 3 QUIT
• Core dumping
• 9 KILL
• 15 TERM
• STOP
• TSTP
• Ctrl-Z
• CONT
• USR1
• USR2

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How to send signals to the processes?

• kill -signal pid
• Default signal is TERM or 15
• ps auxw grep emacs
• weesan 857 0.0 0.0 13312 7952 pts/5 S Apr15 005
  emacs
• kill -9 857
• killall -signal process_name
• killall -9 emacs

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Process States

• Runnable (R)
• Ready to be executed
• Sleeping (S)
• Get no CPU time until receiving a signal
• Zombie (Z)
• Exited process whose status hasnt been
  collected
• Display as ltdefunctgt on ps,
• Stopped (T)
• Process stopped by STOP or TSTP signal

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Niceness

• -20 to 19
• A high nice value means a low priority
• Inherited from the parent
• Can increase but not decrease
• Except for root
• For example
• nice -n 1 program
• renice 1 pid

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Monitor Processes

• ps
• A tool for monitoring processes, eg.
• ps auxw less
• ps laxw less
• ps auxw awk -F' ' ' print 1, 2, 10 '
• weesan 560 228
• weesan 563 000
• top
• A good tool to display CPU usage
• top
• top -n 1

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Monitor Processes (cont)

• strace
• Show every system call and signal a process
  receives
• strace -p pid
• lsof
• List open files
• lsof -u userid
• lsof -p pid
• uptime
• Display the current time, how long the system has
  been up, of current users, average system load
  for the pass 1, 5 and 15 mins

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Monitor Processes (cont)

• Runaway processes
• Processes that consume excessive amounts of a
  system resource, such as CPU time or disk space
• How to approach them?
• Use ps, top, strace, lsof to locate them
• renice them
• Stop them by sending STOP signal and resume later
  by CONT signal
• kill them

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Periodic Processes

• cron daemon
• A daemon that run jobs periodically
• Crontab (/etc/crontab, /etc/cron./,
  /var/spool/cron/)
• crontab -l
• crontab -e
• Format
• Min Hour Day Month Weeday Command
• 10 23 mon-fri
  /home/weesan/backup/home.sh
• 30 23 fri
  /home/weesan/backup/import.sh
• 0 /1
  /usr/bin/rdate -s time.nist.gov

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Reference

• LAH
• Ch 4 Controlling Processes
• Ch 8 Periodic Processes