Operating System Long Questions and AnswersHere in this section of Operating System Long Questions and Answers,We have listed out some of the important Long Questions with Answers on System administration commands of UNIX which will help students to answer it correctly in their University Written Exam.

Lists of Long Descriptive type Questions that may be asked in Written Exams.

  • (1) Explain the basic system administration commands of unix

Question-1 Explain the basic system administration commands of UNIX

1 date : – Prints or sets the date and time.

Syntax :- date[options] [+format] [date]

Description :-

  • Display the current date with current time, time zone.
  • The command can also be used with suitable format specifies as arguments. Each format is preceded by a + symbol, followed by the % operator, and a single character describing the 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).

%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.


$ date

Fri Feb 19 09:55:15 IST 2018

$ date +%m


$ date +%h


$ date +%y


$ date +”Date is %D %t Time is %T”

date is 19/02/18Time is 10:52:34

To know the week number of the year,

$ date -V


To set the date,

$ date -s “10/08/2018 11:37:23”

The above command will print Wed Oct 08 11:37:23 IST 2018

2 wall :- send a message to everybody’s terminal.

Syntax :- wall [ message ]

  • Wall sends a message to everybody logged in with their mesg(1) permission set to yes. The message can be given as an argument to wall, or it can be sent to wall’s standard input. When using the standard input from a terminal, the message should be terminated with the EOF key (usually Control-D).
  • The length of the message is limited to 20 lines.

Example : –

$sudo wall message.txt

Using the sudo command to run wall as the superuser, sends the contents ofmessage.txt to all users.

ulimit : Setting limits on file size

Syntax: – ulimit [limit]

Description :-

  • The ulimit command imposes a restriction on the maximum size of the file that a user is permitted to create , so that there is less wastage of disk space.

3 passwd:- It is used to change your password.

Syntax:- passwd

Description :-

  • Passwd changes the password or shell associated with the user given by name or the current user if name is omitted.
  • First user has to insert current password. Then new password will be asked followed by confirm new password field.
  • passwd command can also be used to change the home directory where the path stands for the home directory.

4 suid : – set user id.

Description :-

  • suid (Set owner User ID up on execution) is a special type of file permissions given to a file.
  • Normally in Linux/Unix when a program runs, it inherits access permissions from the logged in user.
  • suid is defined as giving temporary permissions to a user to run a program/file with the permissions of the file owner rather that the user who runs it.
  • In simple words users will get file owner’s permissions as well as owner UID and GID when executing a file/program/command.


$ chmod u+s a.out

$ ls –l a.out

-rwsr-xr-rw 1 eradar eradar121 Feb 2810:00 a.out

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