Linux Users Configuration 使用者設定

Create a new user called 'jenkins' (create account)

sudo adduser jenkins

Delete a user called 'jenkins' (delete account)

sudo deluser jenkins

Add 'jenkins' to sudoer group (join to group)

sudo usermod -aG sudo jenkins

Remove 'jenkins' from sudoer group (delete from group)

sudo gpasswd -d jenkins sudo

Check any groups joined by this user (check joined group)

id jenkins

Check 'jenkins' user id (check userid)

id -u jenkins

Check group file

sudo vi /etc/group

Add 'jenkins' to the sudoers without requiring password all the time

sudo vi /etc/sudoers

jenkins   ALL=(ALL) NOPASSWD: ALL      #add this line

:wq                                    #save and exit 

Linux Networking 網絡功能

> ifconfig

Bring network up

ifconfig <interface> up

Bring network up with specific IP

ifconfig eth0 172.16.25.125

Bring network up with all parameters

ifconfig eth0 172.16.25.125 netmask 255.255.255.224 broadcast 172.16.25.63

Bring network down

ifconfig <interface> down

Simulate network outrage for 500 ms

ifconfig eth0 down; usleep 500; ifconfig eth0 up 

> DNS

Check currently-using DNS server

cat /etc/resolv.conf

Make simple DNS request

host yahoo.com

dig yahoo.com

nslookup yahoo.com 

> IGMP Group + AWK

Complicated Log Simplification with AWK

cat /proc/net/igmp

awk -F' ' 'NF==5 {print "INT " $2} NF==4 {print "GP " $1}' /proc/net/igmp

#explanation: if row num of field = 5, show INT and the second variable

#explanation: if row num of field = 4, show GP and the first variable

 

Vim Notes 筆記

Up / Down / Left / Right

h - move left (←) (not high!)

l - move right (→) (not low!)

j - move up (↑)

k - move down (↓)

H - move to the top of the screen (High)

L - move to the end of the screen (Low)

Move between windows

Ctrl+W then ↑ or ↓ or ← or → - move cursor to next window

Ctrl+W then H or L           - move vertical left right

Ctrl+W then J or K           - move horizontally up down

Move to last line / first line

:$     - move to last line

:0     - move to the first line

:<num> - move to <number> line

Move in the line

HOME or 0 - move to the beginning of the line

$ or END  - move to the end of the line

Switch between tabs

gt - go to next tab

gT - go to previous tab

Ctrl+PgUp - go to previous tab (will conflict with GUI)

Ctrl+PgDown - go to next tab (will conflict with GUI)

Search ignore case

/\ckeyword

Search with case

/\CkEyWord

Search Next

/ or n

Search Previous

? or N

Search keyword under cursor and Jump

*

Jump to variable declaration (a.k.a. go declaration)

gd     #goto declaration

Jump back to previous cursor

g;

Undo / Redo

u / Ctrl+U

Insert new line

o

Replace

Insert or R or r

Reload without saving

:edit! or :e!

Forgot to sudo - gain sudo vim access when you are readonly

:w !sudo tee %

To delete all lines matching a certain regular expression pattern, use

:g/pattern/d

To do the opposite, i.e. only keep those lines matching the pattern, use

:v/pattern/d

And to only temporarily print matching lines, use

:g/pattern

Set mouse enable in .vimrc

set mouse=a #enable

set mouse=c #disable

Set display line number

set number

Get current file path

:echo @%

:echo expand('%:p')

Set Syntax Highlights on bash scripts without shebang

:set syn=sh

During typing, you want autocomplete

ctrl-N in insert mode

Copy even if you're using set mouse=a

This is actually simple: by accessing register "+" or "*" in Linux 

1. select text using any mode
2. yank the text to register +

"+y

Paste even if you're using set mouse=a

This is actually simple: by accessing register "+" or "*" in Linux

1. go to insert mode
2. paste the text from register + (during insert mode)

Ctrl-R and then +

or you can do this (during command mode)

"+p

Find and Replace (Substitute)

Full command

:substitute

Find all occurrence of 'foo' and replace it with 'bar'.

:%s/foo/bar/g

Find each occurrence of 'foo' (in the current line only), and replace it with 'bar'.

:s/foo/bar/g