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  • Writer's pictureblkrishnarao

A Brush up on Unix Fundamentals Part - 02 | Linux Commands | Unix 101

Updated: Apr 16

The following opinions expressed in this post are my own and in no way connected to my employer. 


                                      Commands in a Glimpse (a basic few)


A glimpse on the few widely used unix or linux commands (few are out of date and few need root access)


Use man command to view details on any command

man                  manual; acts as a manual to view info on all commands

cal

calender; to display calender

passwd

password; to change password of current user

ls

list all files and directories

whoami

list account name associated with current login

users

list all users logged in at same time

who

list all users logged in at same time

w

list all users logged in at same time with additional info

logout

system will cleanup everything and break the connection

halt

Brings the system down immediately

init 0

Powers off the system using predefined scripts to synchronize and clean up the system prior to shutdown

init 6

Reboots the system by shutting it down completely and then bringing it completely back up

poweroff

shuts down the system by powering off

reboot

reboots the system

shutdown

shuts down the system

cp

copy

mv

move or rename

rm

remove

wc

word count

cd

change directory

mkdir

make directory

rmdir

remove directory

chmod

to change permissions on files and directories

chown

change owner of a file or directory

chgrp

change group of a file or directory

echo

to print a text/variable

grep

to find a text/string/charecter pattern

lp,lpr

to print a file on paper opposed to screen

lpstat

to view info on printer queue

mail,mailx

to send mail

|

to concatenate multiple unix commands ( cat file|wc -l)

ps

gives detail on processes running

scp

server copy; to copy from 1 server to other

ping

to check response from a host server

ftp

to transfer files (upload/download) from 1 computer to other

telnet

to connect to a server on another site and work, also used to test connectivity

finger

displays info of a user on a particular host



Commonly used commands and their use:


ls -ltr                                 

lists the files in reverse time order i.e, latest files listed last

ls -la                                  

 lists the files including the hidden files

ls -lh                                  

lists the files with size in human readable format

ls -ld                                  

lists the directory details

lp filename                             

prints the output of file on paper via default printer

lp -d printername filename              

prints to specified printer

lpr -p printername filename             

prints to specified printer

lpstat -o                               

displays all jobs in printer queue

lpq                                     

displays printer job information in a different format

mailx -s "subject" emailid              

sends mail to email id with subject specified in -s

uuencode file|mailx emailid             

sends file as an attachment to email id specified

ls -l|grep Aug|sort +4n                

 list files after filtering Aug containing lines and sorts 4th column ignoring the tabs and blanks



PING - sends an echo request to remote host on the network

ping hostname   

It is useful when:

Tracking and isolating hardware/software problems

Testing/managing the network/remote host



FTP Utility (file transfer protocol) - connects to remote host and enables to upload/download  files from/to remote host

ftp hostname 

FTP has its own set of commands:

  1. connect and login to remote host

  2. navigate directories

  3. list directory contents

  4. put and get files

  5. transfer files as ASCII/binary/ebcdic



put filename

upload file from local to remote machine

get filename

download file from remote to local machine

mput filelist

upload more than 1 file from local to remote machine

mget filelist

download more than 1 file from remote to local machine

prompt on    

turns prompt on

dir          

 lists all files in current directory

cd dirname   

change directory in remote machine

lcd dirname  

change directory in local machine

quit         

logout from current login

Eg:

ftp hostname
name: username
password:
(logged in)
dir
              drwxrwxrwx       user1 group1       abc
cd abc
dir
              -rwxrwxrwx        user1 group1    file1.txt
get file1.txt
bye (quit)

TELNET Utility - Provides utility to connect to a computer at another site and work.

telnet hostname
login : user1
password:
$ logout

Also helps in determining if ports are open between source and destination using below as

Eg:

telnet hostname 1521

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