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.

A glimpse on the few widely used unix or linux commands (few are out of date and few need root access)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

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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