linux与shell 4.检测系统进程 5.理解shell

认识shell

查看已安装的shell

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ cat /etc/shells
# /etc/shells: valid login shells
/bin/sh
/bin/bash
/usr/bin/bash
/bin/rbash
/usr/bin/rbash
/bin/dash
/usr/bin/dash
/usr/bin/sh
/usr/bin/pwsh
/opt/microsoft/powershell/7/pwsh
/bin/zsh
/usr/bin/zsh
/usr/bin/tmux
/usr/bin/screen

查看系统默认shell

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ which sh
/usr/bin/sh
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ls -l /usr/bin/sh
lrwxrwxrwx 1 root root 4 Sep  1 22:11 /usr/bin/sh -> dash

显示当前的shell名称

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ echo $0
bash

输入shell的名称即可切换bash
exit退出bash

shell的父子关系

PID 当前进程的ID
PPID 当前进程的父进程的ID
 
ps --forest 查看继承关系
ps -f 查看进程的常用详细信息
ps -l 详细信息
 
实时查看进程 top 
结束进程 kill PID

例

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
kali     10114 10113  0 Dec26 pts/0    00:00:00 bash
kali     10341 10114  0 14:39 pts/0    00:00:00 ps -f
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ bash
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
kali     10114 10113  0 Dec26 pts/0    00:00:00 bash
kali     10342 10114  1 14:39 pts/0    00:00:00 bash
kali     10345 10342  0 14:39 pts/0    00:00:00 ps -f
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ps --forest
  PID TTY          TIME CMD
10114 pts/0    00:00:00 bash
10342 pts/0    00:00:00  \_ bash
10346 pts/0    00:00:00      \_ ps
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ exit
exit
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ps -f
UID        PID  PPID  C STIME TTY          TIME CMD
kali     10114 10113  0 Dec26 pts/0    00:00:00 bash
kali     10347 10114  0 14:39 pts/0    00:00:00 ps -f

进程列表

命令列表(命令间用分号分隔)

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ pwd;cd /etc;pwd;echo $BASH_SUBSHELL
/mnt/e/Edgedownload
/etc
0

进程列表(将命令列表放入小括号中)

生成一个子shell执行命令。可以嵌套括号生成子子shell
如何查看是否生成子shell？echo $BASH_SUBSHELL,非0为子shell。

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ (pwd;cd /etc;pwd;echo $BASH_SUBSHELL)
/mnt/e/Edgedownload
/etc
1

灵活运用子shell

后台模式(在命令行末尾加上&，将命令置于后台)

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ sleep 1000&
[1] 10350
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ jobs
[1]+  Running                 sleep 1000 &

[1] 后台作业号
10350 PID

jobs 查看所有后台进程

将进程放入后台后，终端不再与子shell的IO绑定

协程(coproc)

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ coproc sleep 10;ps --forest
[1] 10354
  PID TTY          TIME CMD
10114 pts/0    00:00:00 bash
10354 pts/0    00:00:00  \_ sleep
10355 pts/0    00:00:00  \_ ps

coproc与嵌套子进程

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ coproc (sleep 10;sleep 2)
bash: warning: execute_coproc: coproc [10365:COPROC] still exists
[4] 10367
 
[2]   Done                    coproc COPROC ( sleep 10 )
[3]   Done                    coproc COPROC ( sleep 10 )
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ ps --forest
  PID TTY          TIME CMD
10114 pts/0    00:00:00 bash
10367 pts/0    00:00:00  \_ bash
10368 pts/0    00:00:00  |   \_ sleep
10369 pts/0    00:00:00  \_ ps

协程命名

# 默认名称
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ coproc sleep 10;jobs
[1] 10375
[1]+  Running                 coproc COPROC sleep 10 &
 
# 自定义名称 注意格式{空格xxx;空格}
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ coproc MY_COPROC { sleep 10; }
[1] 10372
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ jobs
[1]+  Done                    coproc MY_COPROC { sleep 10; }

外部命令和内建命令

使用type -a 命令名查看是外部命令还是内建命令
使用which 查看当前使用命令的安装位置

外部命令

位于 .../bin 文件夹中
执行时衍生(创建子进程)

内建命令

和shell集成的命令，高效

例

┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ type -a echo
echo is a shell builtin  <--echo是内建命令
echo is /usr/bin/echo
echo is /bin/echo
 
[1]+  Done                    coproc COPROC sleep 10
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ which echo
/usr/bin/echo  <--当前使用的echo是外部命令
 
┌──(kali㉿DESKTOP-FQ0BCLS)-[/mnt/e/Edgedownload]
└─$ type -a ps
ps is /usr/bin/ps  <--ps是外部命令
ps is /bin/ps

两个常用的内建命令

history 查看历史使用的命令行
alias 设置命令行别名