# CPU Load

Uptime Load Averges The sum of number of processes that are currently running plus the number that are waiting.On multi-processor system, the load is relative to the number of processor cores available. The “100% utilization” mark is 1.00 on a single-core system, 2.00, on a dual-core, 4.00 on a quad-core, etc.

uptime                          # Display load averages in 1, 5, 15 minutes based on number of cores/processors

Good Article explaining this: http://blog.scoutapp.com/articles/2009/07/31/understanding-load-averages

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• Physical memory usage stats:

  Mem:   4051792k total,  4026104k used,    25688k free,   359168k buffers
  

  Memory stats line gives you a summary of how much physical memory you have on your system, and how much of it is currently used or available for the use. Modern Linux systems are buffering quite a lot for improved performance, which means you rarely get to see all your physical RAM free – the more your system stays up and running, the more of its recently used data ends up being buffered.

• CPU(s) status

  Cpu(s):  0.6%us,  0.5%sy,  0.0%ni, 97.3%id,  1.6%wa,  0.0%hi,  0.0%si,  0.0%st
  

  Current CPU state, averaged for the number of CPUs installed in your system us – User CPU time. The time the CPU has spent running users’ processes with default priorities sy – System CPU time. The time the CPU has spent running the kernel and its processes ni – Nice CPU time. The time the CPU has spent running users’ proccess that have been prioritized up using nice command id – Idle CPU time wa – I/O wait. Amount of time the CPU has been waiting for I/O operations to complete hi – Hardware IRQ. The amount of time the CPU has been servicing hardware interrupts si – Software Interrupts. The amount of time the CPU has been servicing software interrupts st – Steal Time. The amount of CPU ’stolen’ from this virtual machine by the hypervisor for other tasks (such as running another virtual machine)

• List of the tasks (processes) running on your system

  PID  USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  7629 greys     20   0  749m 291m  28m S    1  7.4  16:51.40 firefox
  

  PID – process ID USER – username for the owner of each process PR – process priority (RT means a Real Time priority class – used for system processes) NI – priority set by nice utility VIRT – the amount of virtual memory used by a process: code, data and shared libraries plus pages that have been swapped out RES – the resident part of a process – how much of it resides in the physical memory (non-swapped memory) SHR – shows you the size of potentially shared memory segments for a process S – the current state of each process %CPU – percentage of the time shares CPU spends running a particular process %MEM – percentage of the physical memory of your system which is used by each process %TIME+ – total time CPUs spent running each process COMMAND – a command used to initiate each process.

# Disk Usage

df

df -hT           # Show info on file system -h human readable and -T type of file system

du

du -Sh /home | sort -rh | head -5       # Display the largest folders/files including the sub-directories
# Perl hack: To display large files with stars
du -k | sort -rn | head -10 | perl -ne 'if ( /^(\d+)\s+(.*$)/){$l=log($1+.1);$m=int($l/log(1024)); printf  ("%6.1f\t%s\t%25s  %s\n",($1/(2**(10*$m))),(("K","M","G","T","P")[$m]),"*"x (1.5*$l),$2);}'

find Find file over certain size

find /home -type f -size +10000k -exec ls -lh {} \; | awk '{ print $5 ": " $9 }' | sort -nr | head -10

# Memory

free Show available memory. Modern Linux use cache and buffering to improve performance. Linux counts cached RAM, Buffered RAM to used RAM. Buffers represent how much portion of RAM is dedicated to cache disk blocks. Cached is similar like Buffers, only this time it caches pages from file reading.

Buffers are associated with a specific block device, and cover caching of filesystem metadata as well as tracking in-flight pages. The cache only contains parked file data. That is, the buffers remember what's in directories, what file permissions are, and keep track of what memory is being written from or read to for a particular block device. The cache only contains the contents of the files themselves.

free -wh
              total        used        free      shared     buffers       cache   available
Mem:            15G        7.7G        4.8G        154M        484M        2.6G        7.3G
Swap:          7.9G          0B        7.9G

# Network

netstat -tulpn                      # Find services listening
netstat -tulpn | grep :80           # Find services listening on a port 80
fuser 7000/tcp                      # Find out the processes PID that opened tcp port 7000

# Stress Testing

# CPU

Fork md5sum 4 times (to use up 4 cores) for 5 seconds

# Mostly userland cpu load
seq 4 | xargs -P0 -n1 timeout 5 md5sum /dev/zero
# High kernel (sys) load from the many write() system calls
seq 4 | xargs -P0 -n1 timeout 5 yes > /dev/null