Basic commands

 Basic commands

A virtual console is a command line where you can log into and control Linux. As RHEL is a multi terminal operating system, you can log into Linux, even with the same user ID, several times.

There are 7 terminals for Linux. 6 terminals are non - GUI and 1 terminal for GUI access. You can login to each terminal using Alt + Ctrl + F1 , F2, .. F7. Each terminals will request your username and password for login. If you want to use the shell in the graphical interface (GUI), press Alt + F2 and type "konsole". As a user you will have permission to access only your /home/user directory and other directories in it.

pwd command:
     pwd - Print Working Directory. pwd command prints the full filename of the current working directory.

Syntax
  The Syntax is  pwd [options]
Options

-P	The pathname printed will not contain symbolic links.
-L	The pathname printed may contain symbolic links.

Example:

Displays the current working directory.

root@raju~]#pwd

If you are working in home directory then, pwd command displays the current working directory as /home.

who command
      who command can list the names of users currently logged in, their terminal, the time they have been logged in, and the name of the host from which they have logged in.

Syntax
  The Syntax is
     who [options] [file]
Options     

am i	Print the username of the invoking user, The 'am' and 'i' must be space separated.
-b	Prints time of last system boot.
-d	print dead processes.
-H	Print column headings above the output.
-i	Include idle time as HOURS:MINUTES. An idle time of . indicates activity within the last minute.
-m	Same as who am i.
-q	Prints only the usernames and the user count/total no of users logged in.
-T,-w	Include user's message status in the output.

cal command:
     cal command is used to display the calendar.
Syntax
  The Syntax is
     cal [options] [month] [year]
Options

-1	Displays single month as output.
-3	Displays prev/current/next month output.
-s	Displays sunday as the first day of the week.
-m	Displays Monday as the first day of the week.
-j	Displays Julian dates (days one-based, numbered from January 1).
-y	Displays a calendar for the current year.

date command
     date command prints the date and time
Syntax  The Syntax is
     date  [options] [+format] [date]
Options     

-a	Slowly adjust the time by sss.fff seconds (fff represents fractions of a second). This adjustment can be positive or negative.Only system admin/ super user can adjust the time.
-s date-string	Sets the time and date to the value specfied in the datestring. The datestr may contain the month names, timezones, 'am', 'pm', etc.
-u	Display (or set) the date in Greenwich Mean Time (GMT-universal time).

Format:

%a	Abbreviated weekday(Tue).
%A	Full weekday(Tuesday).
%b	Abbreviated month name(Jan).
%B	Full month name(January).
%c	Country-specific date and time format..
%D	Date in the format %m/%d/%y.
%j	Julian day of year (001-366).
%n	Insert a new line.
%p	String to indicate a.m. or p.m.
%T	Time in the format %H:%M:%S.
%t	Tab space.
%V	Week number in year (01-52); start week on Monday.

Example:

1.     date command 

date

The above command will print wed Nov 28 10:52:34 IST 2012

2.     To use tab space:

date +"Date is %D %t Time is %T"

The above command will remove space and print as
Date is 11/28/12 Time is 10:52:34

3.     To set the date,

date -s "11/28/2012 11:37:23"

The above command will print wed Nov 28 11:37:23IST 2012

clear command     This command clears the terminal screen.
Syntax  

The Syntax isclear
Options     

There is no options for clearscreen command.
Example

1.     clear

clear command clearscreen like cls command.

2.     You can also have alias for this command.

alias c='clear'

c is the alias name for clear command.

hostname command

     hostname specifies the name of the host.
Syntax  The Syntax is
     hostname [-a | -d | -f | -h | -i | -s]
Options  

-a	Displays the alias name of the host, if used.
-d	Displays DNS domain name
-f	Displays fully qualified domain name.
-h	Displays help message.
-i	Displays IP address of the host.
-s	Trim domain name from display.

Example

1.     hostname command

hostname

The above command will print as raju.com

2.     hostname -a

The above command will remove space and print as raju

3.     To display DNS domain name

 hostname -d

The above command will print as .com