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CentOS Cheat Sheet Cheat Sheet by

Cheat sheet to help with commands
linux

Help Commands

whatis
Search whatis database for complete words; used to find short descri­ptions of system commands
which
Shows the full path to shell commands
wher­eis
Locate binary, source and man pages for a command
apro­pos
Search through a database of short descri­ption to find help and man pages containing certain terms and commands
man
Manual pages for commands

Bash Variables

env
List current enviro­nment variables
echo $NAME
Output value of $NAME variable
export NAME=­value
set $NAME to value in enviroment
set
Change value of shell atrributes and positional parameters or display list of shell variables and functions
$PATH
Exectuable search path
$HOME
Home directory
$SHELL
Current shell

Partitions and Disk Management

df
Report file system disk space usage
mount
Show whats mounted or mount a file system
unmo­unt
Unmount a file system
fuser
Identifies processes using files or sockets
isof
list open files on the system
 

Directory Operations

clear
clears your screen
pwd
Shows current directory
cd
Change direct­ories
ls
List directory contents
mkdir
Create a new directory
rmdir
Delete an empty directory

File Operations

cat
Print a file on the screen, concat­enate files
touch
Create an empty file, change file timestamps
cp
Copy direct­ories or files
mv
Moves direct­ories or files
rm
Removes direct­ories or files (This is how you remove recurs­ively)
ln
Creates a symbolic or hard link for a file
less
View a file on page at a time, allows for going backwards
head
Print the first 10 lines of a file
tail
Print the last 10 lines of a file
wc
Count the number of words or characters in a file
stat
Display file of file system status
cut
Remove sections from lines of input
paste
Merge lines of files

Searching Files

grep
Search text files for lines containing a matching pattern
locate
Find files by matching the whole path name
find
search for files in a directory hierarchy

Commands to know

uname
Prints inform­ation about a machine and operating system it is run on
who
Print who is currently logged in
uptime
Prints system uptime and load
sudo
Execute a command as another user, usually with higher permis­sions
shut­down
Bring the system down in a safe way
 

ls Options

-a
Show all (including hidden)
-R
Recursive list
-r
Reverse order
-t
Sort by last modified
-S
Sort by file size
-l
Long listing format
-1
One file per line
-m
Comma-­sep­arated output
-Q
Quoted output

grep Options

-i
Case insens­itive search
-r
Recursive search
-v
Inverted search
-o
Show matched part of file only

Process Management

ps
Report on current processes
pstree
Display a tree of processes
top
Show real time processes
kill
Terminate a process by PID
kill­all
Kill a process by name
pkill
Look up or signal processes based on same and other attributes
pgrep
Grep for process inform­ation
ctrl+z
Stop the job but don't end process
&
Place this after a command to put the process in the background
jobs
Display all jobs

File Permis­sions

chmod 775 file
Change file permis­sions to 775
chmod -R 600 folder
Recurs­ively chmod folder to 600
chown user.g­roup file
Change file owner to user and group to group

File Permission Numbers

First number is the owner permis­sion, second is group and third is ever­yone
Calculate permission digits by adding number below:
suid=4
421
421
421
sgid=2
rwx
rwx
rwx
flag=1
owner
group
world
example: cmod 777 /etc/­fil­e.txt
 

Networking Direct­ories

/etc­/sy­sco­nfi­g/n­etw­ork­-sc­ripts
This folder contains the config­uration files for each interface on the system; usually named ifcfg-eth0 or ifcfg-­eth1.
/etc­/re­sol­v.c­onf
This file contains the permanent Domain Name Server (DNS) settings

Networking

ifco­nfig
Configure network interface
route
Show/M­ani­pulate the IP routing table
ip
Show/M­ani­pulate routing, devices, policy and tunnels; replaces ifconfig, arp, and route
ifup
Bring network interface up
ifdown
Bring network interface down
ping
Send ICMP ECHO_R­EQUEST to network hosts

Accounts and Security Admini­str­ation

grou­padd
Create a new group
grou­pdel
Delete a group
grou­pmod
Modify definition of a specified group
user­add
Create a new user
user­del
Delete a user
user­mod
Modify a user account
passwd
Update a user's password
vipw
Edit password, group, shadow­-pa­ssword (Updates etc/sh­adow)
vigr
Edit password, group, shadow­-group (Updates etc/gs­hadow)
chage
Change password policy

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