Lecture 9 Processes¶

9.1 Introduction¶

A process is a program in execution
A process is created every time you run an external command and is removed after the command finishes its execution

9.2 Running Multiple Processes Simultaneously¶

Processor Scheduler
- The operating system code that implements the CPU scheduling algorithm （进程调度算法，给进程分配时间片）
Dispatcher
- The OS code that takes the CPU away from the current process and hands it over to the newly scheduled process
Process’s Priority value is computed by Nice value and CPU usage
- 如果一个进程使用的CPU时间越多，优先级越低
Nice value is a integer between -20 and 19 （用户控制的静态优先级值，动态值为系统自动计算）
- nice –n nice_value command

9.2.1 `ps` 查看终端的进程¶

s193157@GOJ:~$ ps
  PID TTY          TIME CMD
 7449 pts/16   00:00:00 bash
14618 pts/16   00:00:00 ps

PID 进程ID
TTY 进程和哪个终端相关联
TIME 进程使用的CPU时间(真正给进程分配的CPU时间,如为0则不到一秒钟)
CMD 进程名

# 列出进程更为详细的信息
s193157@GOJ:~$ ps -l
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1963  7449  7448  0  80   0 -  6991 wait   pts/16   00:00:00 bash
0 R  1963 14821  7449  0  80   0 -  8119 -      pts/16   00:00:00 ps

第一列:0是普通用户的进程, 1是管理员和系统进程
第二列:当前进程的状态 R(运行) S(阻塞)
UID :创建者ID
PPID:父进程ID
C:使用CPU时间
PRI:优先级值 越低,优先级越高 
NI:初始优先级值
ADDR:地址
SZ:占用内存的大小
WCHAN:进程状态

# 给进程降低优先级
s193157@GOJ:~$ nice -n 10 ps -l
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1963  7449  7448  0  80   0 -  6991 wait   pts/16   00:00:00 bash
0 R  1963 14838  7449  0  90  10 -  8119 -      pts/16   00:00:00 ps
# 普通用户只能给进程降低优先级,不能提高优先级,保证系统的关键进程得到资源
s193157@GOJ:~$ nice -n -10 ps -l
nice: 无法设置优先级: 权限不够
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1963  7449  7448  0  80   0 -  6991 wait   pts/16   00:00:00 bash
0 R  1963 14878  7449  0  80   0 -  8119 -      pts/16   00:00:00 ps
s193157@GOJ:~$ ps -e
# 显示当前系统中所有的进程

9.2.2 `top` 动态查看系统中的进程¶

9.2.3 `pstree` 查看进程树¶

9.3 Unix Process States¶

A UNIX process can be in one of many states , as it moves from one state to another , eventually finishing its execution(normally or abnormally) and getting out of the system

Swapped：存储到硬盘中
Zombie：进程结束后，无法自己释放 PCB ，当子进程退出的时候，由父进程释放子进程的资源（给父进程发出信号）

9.4 Execution of shell Commands¶

A shell command can be external or internal

An internal (built-in) command（内部命令） is one whose code is part of the shell process
- bg, cd,continue, echo, exec
An external command（外部命令） is one whose code is in a file; contents of the file can be binary code or shell script
- grep,more ,cat, mkdir, rmdir, ls
type ：查看命令类型

s193157@GOJ:~$ type echo
echo 是 shell 内建
s193157@GOJ:~$ type rmdir
rmdir 是 /bin/rmdir

A UNIX process can create another process by using the fork system call, which creates an exact main memory map of the original process

The forking process is known as the parent process
The created (forked) process is called the child process

当执行 ps 命令后，bash 是 ps 的父进程（因为 ps 的 PPID 等于 bash 的 PID）

s193157@GOJ:~$ ps -l
F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
0 S  1963  7449  7448  0  80   0 -  6991 wait   pts/16   00:00:00 bash
0 R  1963 15337  7449  0  80   0 -  8119 -      pts/16   00:00:00 ps
s193157@GOJ:~$ ps
  PID TTY          TIME CMD
16131 pts/29   00:00:00 bash
17462 pts/29   00:00:00 ps

执行二进制文件

执行脚本文件：需要一个子进程

9.5 Process switch¶

Foreground and Background Process
Run a process in the background
- Append an ampersand(&) to the command line
suspended Foreground process：CTRL+Z
kill Foreground process：CTRL+C
Display all jobs status：jobs
- Background \(\to\) Foreground
  - fg [%jobnum]
- suspended \(\to\) Background
  - bg [%jobnum]

s193157@GOJ:~$ jobs
[1]+  已停止               /tmp/count > /dev/null
[2]-  运行中               /tmp/count > /dev/null &
# 有加号的是刚刚停止的
# 直接用 fg 切换刚刚停止的任务到前台
# fg %2 切换2号到前台

9.6 UNIX Daemons¶

提供系统服务，精灵进程（守护进程）
进程名称以 d 结尾

9.7 Sequential and Parallel Execution of Commands¶

cmd1;cmd2;…;cmdN
- Purpose: Execute the ‘cmd1’, ‘cmd2’, ‘cmd3’,…,’cmdN’ commands sequentially
cmd1& cmd2&…cmdN&
- Purpose: Execute commands ‘cmd1’,cmd2’,…’cmdN’ in parallel as separate processes
UNIX allows you to group commands and execute them as one process by separating commands using semicolons and enclosing them in parenthesis. This is called command grouping.
- (cmd1;cmd2;…cmdN)
- Purpose: Execute commands ‘cmd1’,’cmd2’…,’cmdN’ sequentially but as one process

9.8 Abnormal Termination of Commands and Processes¶

Can terminate a foreground process by <Ctrl-C>
Can terminate a background process:
- Use the kill command
- By first bringing the process into foreground by using the fg command and then pressing <Ctrl-C>
A process can take one of three actions upon receiving a signal
- Accept the default action as determined by the UNIX kernel （默认方式处理）
- Ignore the signal
- Intercept the signal and take a user-defined action（使用自己的方式处理）

内部信号和外部信号

A signal caused by an event internal to a process is known as an internal signal or trap.
- 指针异常、除数为 \(0\)
A signal caused by an event external to a process is called an external signal
kill [-signal_number] proc-list
Kill –l Purpose: Send the signal for ‘signal_number’ to processes whose PIDs or jobIDs are specified in the ‘poc-list’; jobIDs must start with %.The command kill –l return a list of all signals and their names (on some systems, numbers are not displayed)
Commonly used signal_numbers:

1           Hangup
2           Interrupt(<Ctrl-C>)
3           Quit(<Ctrl-\>)
9           Sure kill(所有进程都不能忽略这个信号量)
15          Software signal (default signal number)

每个用户只能给自己的进程发送信号量，超级用户可以给所有进程发送信号量
杀死所有进程 killall

s193157@GOJ:~$ killall count
[2]   已终止               /tmp/count > /dev/null
[3]   已终止               /tmp/count > /dev/null
[4]   已终止               /tmp/count > /dev/null
[5]   已终止               /tmp/count > /dev/null
[6]   已终止               /tmp/count > /dev/null
[7]   已终止               /tmp/count > /dev/null
[8]   已终止               /tmp/count > /dev/null
[9]   已终止               /tmp/count > /dev/null
[10]   已终止               /tmp/count > /dev/null
[11]   已终止               /tmp/count > /dev/null
[12]-  已终止               /tmp/count > /dev/null
[13]+  已终止               /tmp/count > /dev/null

s193157@GOJ:~$ /tmp/neverdie &
[1] 23975
s193157@GOJ:~$ /tmp/neverdie &
[2] 23976
s193157@GOJ:~$ /tmp/neverdie &
[3] 23977
s193157@GOJ:~$ killall neverdie
I won't Die!!!
I won't Die!!!
I won't Die!!!
s193157@GOJ:~$ killall -9 neverdie # 使用9选项终止
[1]   已杀死               /tmp/neverdie
[2]-  已杀死               /tmp/neverdie
[3]+  已杀死               /tmp/neverdie

nohup commands [args] 忽略挂起信号量
- Purpose: Run ‘command and ignore the hang-up signal

9.9 Scheduling a Process To Execute Later¶

计划任务：数据备份

Create	at time	crontab -e
List	`at -l`	`crontab -l`
Details	`at -c jobnum`
Remove	`at -d jobnum`	`crontab -r`
Edit		`crontab -e`

One-time jobs use at ：一次性任务

s193157@GOJ:~$ at 23:59 # 在这个时间创建计划任务
warning: commands will be executed using /bin/sh
at> backup
at> /tmp/count
at> <EOT> # Ctrl+D
job 15 at Tue Jun  1 23:59:00 2021

s193157@GOJ:~$ at -l # 查看自己计划任务
15      Tue Jun  1 23:59:00 2021 a s193157

s193157@GOJ:~$ at -c 15 # 查看计划任务具体内容
#!/bin/sh
# atrun uid=1963 gid=1689
# mail s193157 0
.....
backup
/tmp/count

s193157@GOJ:~$ at -d 15 # 删除计划任务

recurring jobs use crontab ：周期执行任务

s193157@GOJ:~$ crontab -e
no crontab for s193157 - using an empty one

Select an editor.  To change later, run 'select-editor'.
  1. /bin/nano        <---- easiest
  2. /usr/bin/vim.basic
  3. /usr/bin/vim.tiny
  4. /bin/ed

Choose 1-4 [1]: 1

# For example, you can run a backup of all your user accounts
# at 5 a.m every week with:
# 0 5 * * 1 tar -zcf /var/backups/home.tgz /home/

9.10 File Package 文件压缩¶

打包文件

s193157@GOJ:/tmp$ tar -zcvf f.tar.gz /tmp/f
tar: 从成员名中删除开头的“/”
/tmp/f/
/tmp/f/f2
/tmp/f/f1

查看压缩文件的文件结构

s193157@GOJ:/tmp$ tar -ztvf f.tar.gz
drwxrwxr-x zq/zq             0 2021-06-08 08:51 tmp/f/
-rw-rw-r-- zq/zq             6 2021-06-08 08:50 tmp/f/f2
-rw-rw-r-- zq/zq             6 2021-06-08 08:50 tmp/f/f1

解压压缩文件

s193157@GOJ:/tmp$ tar -zxvf f.tar.gz

Last update: August 27, 2023
Created: August 27, 2023