4.0

first thing you always do

• whoami

• hostname

• pwd

find directory, file size, who owns it, what group it belongs to

ls -l

delete a file

rm -f <file>

delete a directory

rm -r <dir>

create a directory

mkdir <name>

check options of a command

man <command>

3 types of file permissions

read, write, execute

each file permission can be controlled at 3 levels

user, group, other

command to change file permissions

chmod ugo+rwx

in file permissions first 3 bits, 2nd 3 bits, 3rd 3 bits

user, group, other

read a file

cat <file>

there are 2 owners of a file

user or group

change ownership of a file

chown <new-owner> <file>

change group ownership of a file

chgrp <new-group> <file>

log out of root

exit

what is an acl?

Access control list - flexible permision instead of u (every user) you can create an ACL for that specific user

show acl's

getfacl

use ACL to add permission for user

setfacl -m u:user:rwx /path/to/file

Add file permissions for a specific group

setfacl -m g:group:rwx /path/to/file

allow all files in an ACL to be cascading

setfacl -rm <u,g:name:rwx:> /path/to/dir

remove a specific acl entry

setfacl -x u:user:rwx

remove all acl entries from everyone

setfacl -b /path/to/file

3 types of help commands

• whatis <command>

• <command> --help

  • man <command>

use a help command

whatis <command>

man <command>

list all files that start with j

ls j<tab-key>

auto-complete commands

tab key

get all commands that start with

hit tab key TWICE

3 simple ways to add texts to files

• vi

• redirects » or <

• echo

What is the difference between Chmod and setfacl

• chmod only allows broad

• Acl’s let you set specific file permissions

why do you do » instead of >

because if you only use > it’ll overwrite what you wrote

3 types of redirects in linux

• standard input

• standard output

  • error

file descriptor # stdin

0

file descriptor # stdout

1

stderr file descriptor #

2

the output of a command can be routed to a file using

>

route the output of ls -l to a file

ls -l > file

view hidden files

ls -la

when a command is executed on the keyboard

stdin - 0

when a command is displayed on the screen

stdout - 1

if a command showed an error message

stder - 2

Tee command is used to

store and output at the same time (it’s like saving a redirect »)

why do you do | tee -a

-a = append → same thing as » vs >

tee command syntax

ls -l | tee -a

find how many characters you have in a file

wc -c <file>

use a pipe command

ls -l | more

view the end of a command output

ls -l | tail

view output one page at a time

ll | more

execute multiple commands

ls ; cd ; pwd

copy a file

cp <source> <new-name>

copy a file but move it to a different location

cp <file> /path/to/dir

remove a file

rm <file>

rename a file

mv <source> <new-name>

move a files location

mv <source> /path/to

create a directory

mkdir <name

delete a directory

rmdir <name>

remove a directory without using rmdir

rm -Rf <name>

change group owner of a file

chgrp <newowner> <file>

change the file owner

chown <new-owner> <file>

change owner/group of a file in one command line

chown <owner>:<group> file

read one page at a time

more <file>

get prompt back when using more command

q

read a file one line at a time

less <file>

What is the difference between the more command and less command

• more = one page at a time

• less = one line at a time

view the end of a file

tail -2 <file>

view the top of a file

head -2 <file>

get the first character of each line in a file

cut -c1 <file>

get a range of characters out of a file

cut -c1-3 <file>

get multiple ranges of characters out of a file

cut -c1-3, 6-8 <file>

what is a delimiter

what seperates lines like → :

where is the delimiter in cut -d: -f # <file>

What does -f stand for?

• delimiter → :

  • -f stands for field

get characters out of a file by specifying the delimiter

• cut -d: -f # <file>