====== Identify Cpu Memory Intensive Processes Adjust Process Priority With Renice And Kill Processes ======

**General Information**

Process wrangling. Get em cow-poke and watch out for zombies.

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===== Identify CPU/memory intensive processes =====

==== pgrep ====

Grep for processes and return the PID.

\\
Search processes for httpd
<code bash>
pgrep httpd -l
</code>
  * Returns PID (default) and name (-l)

\\
Search for all processes being run by the user called "user"
<code bash>
pgrep -u user -l
</code>

\\
All processes not owned by the root user
<code bash>
pgrep -v -u root -l
</code>

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==== ps ====

All processes, user defined display options
<code bash>
ps -eo pid,comm,nice
</code>
  * -e => every (all) processes
  * -o => user defined format

\\
GNU Style Options
<code bash>
ps -elf
</code>
  * -e => every (all) processes
  * -l => long format
  * -f => full format listing (adds STIME column and displays CMDs full paths)

\\
BSD Style Options
<code bash>
ps aux
</code>
  * a => eliminate the "only yourself" restriction
  * u => display user oriented format
  * x => eliminate the "must have tty" restriction

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==== system load ====

Load average
  * percentage of processing power used
  * Number of CPUs is important

\\
Get the number of CPUs
<code bash>
grep -c proc /proc/cpuinfo
</code>
  * -c => count of matched lines
  * proc => the string searched for in /proc/cpuinfo

\\
View load averages
<code bash>
w

OR

uptime
 17:03:49 up  2:02,  1 user,  load average: 0.00, 0.01, 0.04
</code>
  * shows the: last minute, last 5 mins, last 15 mins load
  * last min = 0%, last 5 mins = 1%, last 15 mins = 4%
  * If 2 cpus, a load average of 1.00 would be 50% CPU load. (1.00 / 2 = .50)
  * If 2 cpus, a load average of 2.00 would be 100% CPU load. (2.00 / 2 = 1.00)

Percentage of total processing power in use = load average / (# of cpus)

----

==== top ====

Open top
<code bash>
top
</code>
  * Sorted by %cpu used by default

\\
Interactive commands
  * z => toggle colors (easier to see highlighted columns)
  * x => highlight current sort column
  * 1 => expand CPU list to see individual usage
  * M => sort by %memory used
  * P => sort by %cpu used
  * < or > => change sort column
  * r => (renice) enter pid to renice, then nice level (selects top PID by default, can change)
  * k => (kill) enter pid, then signal to send (selects top PID by default, can change)

\\
Start top with a screen update delay of 2 seconds
<code bash>
top -d 2
</code>
  * Default is update the display every 3 seconds

----

===== adjust process priority with renice =====

Highest priority => -20 (the least nice to other processes)\\
Lowest priority => 19 (the most nice to other processes)\\
Default nice level if nice run, but level not specified => 10

\\
Start program with a nice level of 5
<code bash>
nice -n 5 httpd
</code>

\\
Change nice level of a running process to -5
<code bash>
renice -n -5 2879
</code>

\\
Change nice level of all running httpd processes to -10
<code bash>
renice -n -10 $(pgrep httpd)
</code>

----

===== kill processes =====

List kill signals
<code bash>
kill -l
</code>

  * 1 (SIGHUP) => hang up, similar to closing a terminal window
  * 2 (SIGINT) => keyboard interrupt (ctrl+c)
  * 3 (SIGQUIT) => ask process to quit
  * 9 (SIGKILL) => Kill process immediately, not blockable
  * 15 (SIGTERM) => Asks process to terminate cleanly. Default when nothing passed.
  * 18 (SIGCONT) => continue process that was stopped
  * 19 (SIGSTOP) => stop the process, not ignorable
  * 20 (SIGTSTP) => stop that can be ignored

\\
Kill process by name (instead of PID)
<code bash>
pkill httpd
</code>
  * Kills all process ids named httpd, sending signal 15 (SIGTERM)

\\
Remove a user's ssh session (kick user off system)
<code bash>
pkill -u rjones sshd
</code>

\\
Kill all processes started from a specific terminal
<code bash>
pkill -t pts/1
</code>
  * This does NOT kick them off the system, only kills their running programs started from that session.

\\
Stop a process that is job #1
<code bash>
kill -SIGSTOP %1
</code>
  * Alt command: kill -19 %1

\\
Contine the process that is job #1
<code bash>
kill -SIGCONT %1
</code>
  * Alt command: kill -18 %1

\\
Kill an individual process with PID 2594
<code bash>
kill -SIGKILL 2594
</code>
  * Alt command: kill -9 2594

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