Processes and scheduled tasks Task Management

1, the relationship between the program and the process of
(1) program

In the hard disk, an optical disk medium such as executable code and data
Static code saved

(2) process

Program code running in CPU and memory
Code dynamically executed
Parent and the child: Every process can create one or more processes

2, static view process information

[root@localhost ~]# ps aux
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1 0.1 0.3 56640 6672 ? Ss 00:22 0:01 /usr/lib/systemd/systemd --switched-root --system --deserialize 24
root 2 0.0 0.0 0 0 ? S 00:22 0:00 [kthreadd]
root 3 0.0 0.0 0 0 ? S 00:22 0:00 [ksoftirqd/0]
root 5 0.0 0.0 0 0 ? S< 00:22 0:00 [kworker/0:0H]
root 7 0.0 0.0 0 0 ? S 00:22 0:00 [migration/0].

（1）

USER: name of the user account to start the process.
PID: The process PID number in the system, is unique in the current system.
% CPU: The percentage of CPU usage.
% MEM: The percentage of memory usage.
VSZ: occupancy size of the virtual memory swap space.
RSS: occupy permanent memory size of physical memory.
TTY: indicates that the processes are running on which terminal. "?" Represents the unknown or no terminal.
STAT: it shows the current status of the process: D: non-interrupted sleep, S: interruptible sleep, R: ready or running state, T: a suspended state, the Z: zombie state <: high-priority process, N: Low Priority level process, +: the foreground process group of the process, |: first session of the process: multi-threaded process, s
START: Start time of the process.
TIME: The process of CPU time.
COMMAND: name of the command to start the process.

(2) stat state

S: uninterruptible sleep
R: can interrupt sleep
Z: Ready or running
<: Advanced finite process
N: low-priority process
+: The foreground process group of the process
T: suspend state
Z: dead state

3, dynamic process view

top - 00:51:38 up 28 min, 1 user, load average: 0.00, 0.01, 0.03
Tasks: 399 total, 2 running, 397 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.3 sy, 0.0 ni, 99.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 2035356 total, 1760020 free, 134140 used, 141196 buff/cache
KiB Swap: 2097148 total, 2097148 free, 0 used. 1751724 avail Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
722 root 20 0 0 0 0 S 0.3 0.0 0:00.10 xfsaild/dm-0
1 root 20 0 56640 6672 3888 S 0.0 0.3 0:01.31 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/0

top - 16:58:24 [the current system time]
[1:54 system has been running 1 hour 54 minutes]
2 users currently logged in [2] Users
load average: 0.00,0.00,0.00 [System load average: 1 minute, 5 minutes, 15 minutes]
Tasks: 108 total [tasks: 108 total process]
1 running [1] running processes
107 sleeping the sleep process [107]
0 stoppd process stops [0]
[0 0 zombie zombie process (freezing process)]
Cpu (s): 0.0% us user control of CPU [percentage]
0.0% sy [kernel space occupied by the percentage of CPU]
0.0% ni [priority processes within the user process control changed occupancy percentage of CPU]
CPU idle percentage of 100.0% []
0.0% wa [percentage of CPU time to wait for the input and output]
0.0% hi 【】
0.0% and 【】
Men: 1012352k total amount of physical memory 1012352k []
465816k used [used] 465816k physical memory
546536k free physical memory [of] free 546536k
[61064k 61064k buffe used as the kernel cache]
Swap: 2031608k total amount of swap partition 2031608k []
0k used [not] use the swap partition
2031608k free [total] swap free 2031608k
267580k cache swap buffer [total] 267580k
PID: Process ID
USER: User name of the process owner
PR: Priority
NI: nice value. A negative value indicates a high priority, positive values indicate a low priority
VIRT: total amount of virtual memory used by the process in kb
RES: process used, not swapped out of physical memory size, unit kb
SHR: shared memory size in kb
S: Process Status
% CPU: the last update to the current occupancy percentage of CPU time
% MEM: The percentage of physical memory used by the process
TIME +: Total CPU time used by the process, units of 1/100 sec
COMMAND: command

4, the process was started

(1) manual start:

Reception Start: user input commands directly execute the program
Start backstage: Add the "&" symbol at the end of the command line

Front and back scheduling (2) process

Ctrl + Z suspends the current process, that is transferred to the background and stop execution
jobs command to view the list of tasks in the background, at the same time add -l displays the PID number
fg command will restore the background process to the foreground, you can specify the number of job program
bg command will pause the background processes running in the background adjusted

Run (4) to terminate the process

Ctrl + C interrupt command being executed
kill、killall 命令
kill PID to terminate the specified number of processes
killall terminates all processes for the specified name
-9 option forcibly terminated

5, scheduled to start

(1) use the at command, set the time schedule

Service script: /etc/init.d/atd
Formatting: at [HH: MM] [yyyy-mm-dd] to set the day's task plan it does not add date
Basic operation:

Ctrl + D to save and exit
atq query the existing time schedule
atrm [task number] Delete the first several tasks

(2) use the crontab command to set periodic scheduled tasks

Script Name: /etc/init.d/crond
The main configuration file:

Global configuration file: / etc / crontab

Cron task management plans
- Edit: crontab -e [-u username]
- View: crontab -l [-u username]
- Delete: crontab -r [-u username]

Special value representing time
- * Indicates any time within this range
- A plurality of discrete time points, the interval represented by
- - indicates a continuous range of time
- / Frequency specified time interval