Marco Education class 20-2 first week study notes 5

System users
PS1 defines the format of the prompt for example:

Ps1=xxx the current user name will be temporarily modified
echo $PS 1
[\[email protected]\h \w]\$//u represents the user, H host name W current folder

# admin
$ normal User

When we enter a command, it will pass the shell to Kernel,kernel to determine the type of the command.

Command type:

Built-in command: The kernel comes with kernel itself

External command: File installed with GUN files

Check out the kernel

cd/boot/
ll Vmlinuz-3.10.0-327.el7.x86_64-h//h says it's easy to see the size of the data, which is only 5 m, in a way that humans view. All the built-in commands are included here.

[Email protected] ~]# type cat
Cat Is/usr/bin/cat//external commands
[[Email protected] ~]# type type
Type is a shell builtin//built-in command
[[Email protected] ~]# type cd
CD is a shell builtin//built-in command



[Email protected] ~]# type who
Who is/usr/bin/who//external commands
[[email protected] ~]# WHO//Run this command
root:0 2016-07-21 17:06 (: 0)
Root pts/0 2016-07-21 18:55 (: 0)
Root PTS/1 2016-07-21 19:03 (172.18.16.73)
Root PTS/2 2016-07-21 21:32 (172.18.16.73)
[Email protected] ~]# type who
Who is hashed (/usr/bin/who)//hashed: hash, when an external command is run, it is hashed into the cache and can be read quickly the next time it runs.


Type chmod

chmod 000/root/111

Type chmod which chmod can see the path of the command, but which can only find external commands, cannot find built-in commands, such as which type failed

[email protected] ~]# which cat
/usr/bin/cat
[Email protected] ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin
[[Email protected] ~]# type cat
Cat Is/usr/bin/cat
[Email protected] ~]# CP/USR/BIN/CA
Cairo-sphinx Calibrate_ppa Cancel Caribou-preferences Catman
Cal Canberra-boot Cancel.cups Cat
Ca-legacy Canberra-gtk-play Captoinfo CATCHSEGV
[Email protected] ~]# Cp/usr/bin/cat/usr/local/sbin/cat
[[email protected] ~]# Cat 111
[[Email protected] ~]# type cat
Cat is hashed (/USR/LOCAL/SBIN/CAT)

[Email protected] ~]# Rm/usr/local/sbin/cat
Rm:remove regular file '/usr/local/sbin/cat '? Y
[[email protected] ~]# Cat 111
-bash:/usr/local/sbin/cat:no such file or directory//has been looked up according to the path of memory.
[email protected] ~]# which cat
/usr/bin/cat
[[Email protected] ~]# type cat
Cat is hashed (/USR/LOCAL/SBIN/CAT)
[[email protected] ~]#/usr/bin/cat 111//Add a path to it
For a complete solution, you need to resolve it from cache to memory
[email protected] ~]# hash
Hits command
14/usr/bin/screen
1/usr/bin/rm
4/usr/bin/chmod
5/usr/local/sbin/cat
1/usr/bin/touch
3/usr/bin/who
1/usr/bin/cp
2/usr/bin/vi
2/usr/bin/w
2/usr/bin/ls
1/usr/bin/clear
[[email protected] ~]# hash-d cat//hash-r all clear


[[email protected] ~]# hash
Hits command
0/usr/bin/cat//So you can search by default path from the new
Cat 111//OK





[Email protected] ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin//external command the order in which the path to search is placed the first priority is higher, if I want to make APP1 in/usr/local/ Bin as a priority you can
/usr/local/bin/app1 to execute, otherwise do not write the path can not find


chmod $PATH

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/root/bin

Built-in command high priority
Then according to the hash $PATH
To determine the priority level of


Enable-n CD//disable built-in command method
Enable CD/Enabled


[Email protected] tmp]# enable-n CD
[[Email protected] tmp]# type cd
CD is hashed (/USR/BIN/CD)//Because the internal command is not outside the command is still there, CENTOS6 does not support this


Whereis chmod//Search only in Path variable

[email protected] tmp]# ls \
> L \
> Yum.log//For longer commands can be displayed on a branch

[[email protected] tmp]# ls;pwd;ifconfig//For short commands can be executed together and take effect separately


Date:
Show date and time
Date-u//Show GMT

Clock:
Show Hardware Time

Synchronization Time Method:

CLOCK-S//Hardware-based quasi-sync time

CLOCK-W//With system time quasi-synchronization time


Date month day hour minute year second

Date 091811302012.20

For example:

[Email protected] ~]# Date-u
Fri Jul 02:12:11 UTC 2016
[[Email protected] ~]# Date 091011202012.20//manually set a time
Mon Sep 11:20:20 CST 2012
[Email protected] ~]# clock
Fri 10:19:24 AM CST-0.492925 seconds
[[email protected] ~]# clock-s//Check back the correct time by hardware
[[Email protected] ~]# Date
Fri Jul 10:19:33 CST 2016


Cal
command to display the date

[[email protected] ~]# cal 09 1752
September 1752
Su Mo Tu We Th Fr Sa
1 2 14) 15 16
17 18 19 20 21 22 23
24 25 26 27 28 29 30//cause of religious reasons



Cat/etc/issue

[Email protected] ~]# vi/etc/issue
\s
Kernel \ r on an \m
STOP!!! This is MY MY///Added to character interface line entry will appear.

Nano/etc/issue

Loginout =ctrl + D



[[email protected] ~]# systemctl Restart network//restart NIC program

CentOS 7 Command Installation

You can choose to see if the screen is installed on your computer.

Type screen

If not installed, there are two ways to install it:
1: Check that the disc has been mounted, locate the screen-4.1.0-0.21.20120314git3c2946.el7.x86_64.rpm file in the packages package and double-click Install;

2;DF//view disc already mounted
[[email protected] ~]# DF
Filesystem 1k-blocks used Available use% mounted on
/dev/sda2 52403200 3348332 49054868 7%/
Devtmpfs 923776 0 923776 0%/dev
Tmpfs 938316 144 938172 1%/DEV/SHM
Tmpfs 938316 9136 929180 1%/run
Tmpfs 938316 0 938316 0%/sys/fs/cgroup
/dev/sda5 20961280 32932 20928348 1%/testdir
/DEV/SDA1 201388 141756 59632 71%/boot
Tmpfs 187664 187644 1%/run/user/0
/dev/sr0 7587292 7587292 0 100%/run/media/root/centos 7 x86_64

Rpm-i/run/media/root/centos7\7\x86_64/packages/screen-4.1.0-0.21.20120314git3c2946.el7.x86_64.rpm

start experiment after installation

Test Purpose: Help users solve System application problems
the prerequisite for the completion of the test: Both sides have to log on to the same server, and use the same account


Help party:
Type screen //See if Screen
 screen
Screen-s zcl1840 // Open a new screen session:zcl1840 for the linked account

Helper:

which screen//view path of screen

Screen-ls//See if there is a Help account login

Screen-x zcl1840 //Join reply: Join the Help account to establish a link

The two can operate on one desktop after the connection.
The link is interrupted if either side exits the exit.


Creates a background program through screen to prevent interruptions. For example, the upgrade program runs in the background.

simulates
  with infinite loop Yes command;
  1:screen
  2:  Yes
  3:  Ctrl + a  & nbsp; //Pause Press D to turn Yes Infinite loop program into the background
  4:screen-ls //view to Background process program number and random user name Pts-0.centos7
       screen-x  User   //After joining the original background run program is displayed on the desktop
  5:screen-r  session// Restore a process: if there is a background process then R does not add the user name, if there are multiple add the corresponding process name, you can restore the process or CTRL + C End Process
  6: If the process after the end of,screen-r  there is no screen To is resumed   exit

Echo:
Display character commands


[[email protected] ~]# echo AAA BBB CCC
AAA BBB CCC
[[email protected] ~]# echo-n AAA BBB CCC
AAA BBB Ccc[[email protected] ~]#


Variable: Represents a collection of some strings

[Email protected] ~]# echo $UID
0
[[email protected] ~]# echo \ $UID//join "\" to turn meaning
$UID
[Email protected] ~]#

[[email protected] ~]# echo ' $UID '//' strong quote
$UID
[[email protected] ~]# echo "$UID"//"" Weak reference
0
For example:
[Email protected] ~]# echo "Echo $UID"
Echo 0
[Email protected] ~]# echo ' echo $UID '
Echo $UID
[[email protected] ~]# echo ' echo $UID '//This command = $ (echo $UID)
0


ECHO-E//Can let the following string display some special functions

For example:
[[email protected] ~]# echo "AAA \c"
AAA \c//No plus E
[[email protected] ~]# echo-e "AAA \c"
Aaa[[email protected] ~]#//Add e after the \c parameter only takes effect


[Email protected] ~]# echo-e "\a"//\a's role is to make a sound
[Email protected] ~]#

echo Command options:

-N does not wrap characters at the end of the line
-E If the following character appears in the string, it is handled in particular, not as a general text output:
\a issued a warning sound;
\b Backspace key
\c finally not add the line break symbol;
\ n Wraps and the cursor moves to the beginning of the line;
\ r The cursor moves to the beginning of the line, but does not wrap;
\ t Insert tab;
\ \ insert \ Character
\0NNN insert ASCII character represented by NNN (octal)
Echo-e "\033[43;31mabcd \033[0m"//43 for the view, 31 for the font color. I don't use it on the CRT.


\XHH Insert the ASCII character represented by the HH (hex)

Marco Education class 20-2 first week study notes 5