Linux commands

env # to get all env variables


*********to work as root*************
su -
**************ifconfig synonyms------------
ip address show or ip a s or ip a s eth0
************formatted file name************
cp a.txt a_$(date +%F).txt



#to decompress .gz file
gunzip *gz

#check services running
service --status-all (redhat)
#for one service
service <service-name> status/start/restart

sudo chmod -R ugo+rw /DATA/SHARE

change rwx permission types to ug[oa]
eg:
chmod a-w TEST_DEMO.java
chmod a+rwx TEST_DEMO.java

permissions given in binary:
4 Read, 2 Write, 1 Execute
eg:
 chmod 751 TEST_DEMO.java
 chmod 000 TEST_DEMO.java
 
 Get users / cut example
  cut -d: -f1 /etc/passwd
  
  sed 's/:.*//' /etc/passwd
  
  special permission:
  s setuid/setgid permissions - appears in the read portion of user/group
  eg: g+s
  
 [ The sticky bit can be very useful in shared environment because when it has been assigned to the permissions on a directory it sets it so only file owner can rename or delete the said file.]
 
 t - sticky bit - appears in the executable portion of the all users. - only file owner can rename or delete the file
 eg: chmod +t <dir>
 
 
# to execute a last command: !<command>, !ls or !!	
# to view last ls file: vi !$file

vi case insensitive search
/\c searchString
case sensitive search
/\C case sensitive search
 
# to search for a previously executed command:
# ctrl r and type a few letters of the command

# to get from history
  history | grep <command >
  
# grep with regular expression
  egrep "sqoop|hive" *  
find/grep in file recursively, ignoring case, with filename, including/excluding some files 
 grep -riH --exclude "*.java" p_shipment_serial_number 
# while using vi and get out and come back
 ctrl z to get out, and come back to editor fg 1 or fg 2

groups

chmod -R a+X  => capital X means only the directory

df

disc usage rolled up to one level below directories
 du --max-depth=1

tail -20 <filename> 
head -20 <filename> 

To find in sub dir as well:
find . -name "*sh"

to find inside file:
 grep <xxx> <filename>
to find files ignoring case:
find . -iname <filename> 
 to see running processes:
 
 ps
 ps -ef
 kill <processId from above>
 grep top - high usage processes
 
 to see logged in users:
 w
 
 to get information from web:
 
 wget
 
 Calender:
 cal
 
 
 
to see the processs:
ps
  
  
to decompress and extract files:
gunzip test.sh.gz
tar -xvzf snr_split.tar.gz'

to compress and zip files:
tar -cvzf snr_split.tar.gz ~/snr_split


vi search replace
:s/old_string/new_string
replaceAll:
:%s/old_string/new_string

ssh from one machine to another(from namenode to datanode)
ssh <servername>172.16.1.181

https://youtu.be/l0QGLMwR-lY

to know which version we use:
uname

get ipconfig:
old: ifconfig
new: ip addr show

check services status, restart....
old:	service <name> status
new:	systemctl | grep mysql

disc usage:
 du -sh folder
 
 see ports/listening tcp/udp
 sudo netstat -tulpn
 
 cpu usage of processes:
 ps aux | grep <processname>
 top
 htop
 
 checking mounted things:
 mount
 
 system admin commands:
 lsof | head
 lsof /var/log/nginx/access.log
 lsof <processid> | grep log
 lsof <filename> gives which processes are using the file
 lsof -u <username>
 lsof -i :80(port)
 lsof -i tcp
 
 ---------to see class files of a jar--------
jar tvf <jarfile>
-------------------root access -------------
su -

ip address show or ip a s/ 
ip r s -- ip root show

to get date formate = $(date + %F)

--------------to see ports ---------------------
 /etc/services 
 ----------create multiple folders at once---------
 mkdir -p hdp{1,2,3}.test.com
 
 --------------run command while ssh -------------------
 ssh name@domain_name "df -h" to get free space