The Commands about the Processes

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Here will introduce some commands about the Processes:
● ps – Report a snapshot of current processes
● top – Display tasks
● jobs – List active jobs
● bg – Place a job in the background
● fg – Place a job in the foreground
● kill – Send a signal to a process
● killall – Kill processes by name
● shutdown – Shutdown or reboot the system

How a process work

When a system starts up,the kernel initiates a few of its own activities as processes and launches a program init(/etc/init),and the init will start all system services, and many of them are implemented as daemon process(sit in background and just do their own things without having any user interface).
A program can launch other programs is expressed in the process scheme as a parent process producing a child process.
Each process has a PID,the init always getting PID 1.

ps

ps
ps x ##will show all of our processes  no matter which terminal
ps aux ##will give us more information about the CPU/MEM usage,virtual memory size and so on.

top

top will give us dynamic view of the machine’s activities.

top

Controlling processes

jobs will list the jobs that have been launched from our terminal and every job has a number.
if you want to change a process from background to foreground,using fg,like:

fg %num     ##num is the number that the command of jobs shows

bg is similar

kill

kill is used to send signals to programs,the common pattern is like:

kill [-signal] PID

the signal introduces:
- 1:HUP,Hangup
- 2:INT,Interrupt,just like ctrl+c
- 9:KILL
- 15:TERM,Terminate
- 18:CONT，Continue
- 19:STOP

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