Explore topic-wise InterviewSolutions in .

The correct answer is (B) time

For explanation: When there are multiple versions of a program and we want to FIND out how efficiently they’ve used the SYSTEM resources we can USE the time command. The time command accepts the entire command line to be timed as its argument. It executes the command and also displays the time usage on the terminal. For example,

The correct option is (a) True

The explanation is: The cron-tab or cron table is a list of commands that are scheduled to be RUN at REGULAR intervals. The crontab command opens the crontab for scheduling, EDITING, REMOVING, modify scheduled TASKS.

Right answer is (d) crontab -r

To ELABORATE: We can see the CONTENTS of our crontab file using crontab -l COMMAND and can REMOVE them with crontab -r. We can also enter cron COMMANDS using crontab -e command.

Right choice is (c) a daemon

For explanation I would say: CRON is a daemon which runs on UNIX systems. It executes programs at regular INTERVALS. It lets us to SCHEDULE jobs so that they can be scheduled repeatedly. It executes cron jobs created by the crontab. For example, a cron job can be scheduled for PROCESSING logs EVERY evening.

Right option is (d) process which runs automatically WITHOUT any user INTERACTION

The explanation: DAEMONS are processes which RUN automatically without requiring any user interaction. These are designed to help the user by performing tasks which are COMMONLY done. For example, checking for an e-mail.

Right CHOICE is (a) True

Explanation: The batch command ALSO allows us to schedule jobs for later execution but unlike at command, it executes the jobs as soon as the system load permits. Any job scheduled USING batch goes to a special at queue.

The correct option is (a) True

For explanation I WOULD say: Unfortunately, the major drawback in at command is that we cannot find out the name of the program SCHEDULED to be executed. This may create a problem when we are unable to RECALL whether a specific job has actually been scheduled for LATER execution.

The correct option is (a) -r

To explain I would say: Jobs can be listed using -L option with at command and can be removed using -r option. All we have to do is to provide the job NUMBER (of the job which we WANT to remove from the queue) as an argument to at command along with -r option. For example,

The CORRECT CHOICE is (d) at morning

To elaborate: at command offer keywords like now, NOON, midnight, TODAY, tomorrow to schedule jobs according to our CONVENIENCE. For example,

Correct answer is (d) evening

The explanation is: at command offer keywords like now, noon, MIDNIGHT, today, TOMORROW to schedule jobs according to our CONVENIENCE. We can ALSO use the + operator with at command.The words that can be used with + operator include hours, days, month, years, WEEKS.

Right option is (B) at

Easiest explanation: UNIX provides sophisticated FACILITIES to schedule a JOB to run at a specified time of day using at command. at command TAKES as its arguments the time the job is to be executed and displays the > prompt. The input then has to be supplied from STANDARD input. For example,

Right choice is (a) >

To elaborate: The standard output and standard error of the program scheduled using at command are mailed to the user who can use any mail READING program to view it. Alternatively, we can use the > SYMBOL to REDIRECT our output to a SPECIFIED file for viewing it later. For example,

Right CHOICE is (C) jobs

To ELABORATE: We can use the jobs command to list the STATUS of the jobs. This command tells the state of the job along with job NUMBER. For example,

The correct answer is (b) False

For explanation I would say: If we are using the C, KORN or Bash SHELL then we can use their job CONTROL facilities to manipulate jobs LIKE killing a job, pushing to background or foreground, suspending a foreground job. We cannot use these job control COMMANDS in any other shell except the above mentioned.

The correct option is (d) CREATE a NEW job

Easy explanation: If we are using the C, Korn or Bash shell then we can use their job control FACILITIES to manipulate JOBS. Job control in these shells means that we can :

•Relate a job to the background (BG)

•bring it back to the foreground (fg)

•kill a job (kill)

•list the active jobs (jobs)

•suspend a foreground job (ctrl-Z)

Right option is (a) True

Easiest explanation: bg command can also be used with the job number, job name or a string as ARGUMENTS prefixed with the % symbol. For example, if we’ve suspended two jobs but now we WANTTO send the second job to the background, USE the FOLLOWING command:

The correct choice is (b) fg

For explanation I would SAY: We can USE the fg command to BRING any of the BACKGROUND jobs to the foreground. To bring the most RECENT background job to the foreground we can use the following command:

Right choice is (a) BG

Best explanation: If we’d suspended a job using ctrl-Z then after that we can use the bg COMMAND to push the CURRENT foreground job to the background. For EXAMPLE,

Correct ANSWER is (a) ctrl-Z

To EXPLAIN I would say: Suppose we invoke a command and the prompt hasn’t RETURNED even after a LONG time then we can suspend that job by pressing Ctrl-Z. The point needed to be focused here is, the job hasn’t terminated yet; it’s only suspended or STOPPED.

Correct answer is (a) True

Explanation: To view the list of all SIGNAL names and numbers that are AVAILABLE on our machine, we have to USE the -L option with kill command or view the file /usr/include/sys/signal.h

The correct answer is (b) -s

The best explanation: Sometimes it may happen that some programs ignore the SIGTERM signal (15) and continue their execution normally. In such a case, the process can be killed by using SIGKILL signal (9). This signal can’t be generated at the press of a KEY, so we have to use KILLwith the signal name preceded with -s OPTION. For example, to kill a job with PID 184 use the following command:

The correct answer is (c) SIGKILL(9)

The explanation: By default, the SIGTERM signal (15) is USED by the KILL command to terminate processes. But sometimes it may happen that some PROGRAMS ignore it and CONTINUE their execution normally. In such a case, the process can be killed by using SIGKILL signal (9). For example, to kill a job with PID 134 use the following command:

Correct choice is (a) True

The explanation: UNIX often requires to COMMUNICATE the occurrence of events to process. This is done by sending a signal. The SIGTERM signal (15) is the default signal USED by the KILL COMMAND to TERMINATE processes.

The correct choice is (c) kill $!

Explanation: For most SHELLS, the system variable $! Stores the PID of the last BACKGROUND job. So we can kill any PROCESS by USING kill COMMAND. The PID of the job can be seen when & is affixed to a command. For example,

Correct option is (C) kill

The best explanation: The kill command is used for premature termination of a PROCESS. It usually SENDS a signal with the intention of killing one or more processes. kill is an INTERNAL command in most shells. Kill command USES one or more PID’s as its arguments. For example,

Correct option is (b) -N

Best explanation: nice VALUES are system-dependent and TYPICALLY range from 1 to 19. We can also specify the nice value explicitly with the -n option but a non-privileged user cannot increase the priority of a PROCESS. For EXAMPLE, to increase the priority by 8 times use the following command:

Correct choice is (C) built-in

Easiest explanation: NICE is a built-in command in the C shell. nice VALUES are system-dependent and typically range from 1 to 19. A HIGHER nice VALUE implies a lower priority. nice reduces the priority of any process.

Right answer is (a) True

For explanation: UNIX offers the nice command, which is used with the & operator to INCREASE the priority of jobs. More important jobs can have GREATER ACCESS to the system resources. For EXAMPLE,

Correct choice is (d) nice

Explanation: PROCESSES in UNIX system are USUALLY executed with equal PRIORITY but sometimes it is necessary to complete high priority jobs at the earliest. For this purpose, UNIX OFFERS nice command. For example,

Right answer is (B) 1

To explain I would SAY: The shell dies on logging out but it’s child didn’t. The KERNEL handles such situations by reassigning the PPID of the orphan PROCESS to the SYSTEM’s init process (PID 1), which is the parent of all shells.

Right answer is (b) False

The explanation is: Some shells DISPLAY a message when the NOHUP command is used. In these shells, nohup command sends the STANDARD output of the command to the file nohup.out. If you don’t get this message then you have to make sure that you’ve taken care of the output USING REDIRECTION, if necessary.

The correct option is (a) PID

For explanation I would say: When the NOHUP command is USED, the shell returns the PID and some SHELLS also DISPLAY a message. For EXAMPLE,

Right option is (d) C and bash

For explanation I would SAY: Background JOBS are terminated automatically when the user logs out. But in C shell and bash shell jobs are not terminated even after the user logs out. While this is not the case with Bourne and Korn shells. In these shells, jobs are ABORTED as SOON as the user logs out.

Correct option is (a) True

Best explanation: nohup command ALLOWS running JOBS in the background even when the user logs out of the system. But it is necessary to terminate the command line with & when using nohup command.

Correct CHOICE is (c) nohup

To explain I WOULD say: The nohup command when prefixed to a command allows execution of the process even after the user has logged out of the system. Background JOBS cease to run when a user logs out of the system. This happens because the shell is KILLED. To avoid this CONDITION, the nohup command can be used. For example,

Right OPTION is (d) &

The EXPLANATION is: The & is the shell OPERATOR used to run a process in the background. All we have to do is to terminate the COMMAND line with a & symbol, the command will automatically run in the background. For example,

The correct CHOICE is (a) True

The EXPLANATION is: Since UNIX is a multitasking system, it ALLOWS the user to do more than one job at a time. But there can be only one process in the foreground and the rest of jobs have to RUN in the background.

Right answer is (B) exec

Easy explanation: The parent process executes the WAIT() SYSTEM CALL to wait for the child process to complete. It picks up the exit status of the child and then continues with its other functions.

Correct choice is (c) exec

The best I can explain: Forking CREATES a new PROCESS but it is not ENOUGH to RUN a new program. To do so, the forked child needs to overwrite its own images with the code and data of the new program. This mechanism is called exec and the child process is SAID to exec a new program.

Right choice is (b) negative integer

The best explanation: fork() system call is used in UNIX for creating NEW processes. It TAKES no parameters and returns an integer value. The value returned depends on the following cases:

Positive value: returned to the parent process. The value contains PID of child process which is created.

Negative value: returned if the creation of child process is unsuccessful.

Zero: returned to the NEWLY created child process.

The correct answer is (a) True

The best I can EXPLAIN: The process created using fork is PRACTICALLY identical to that of calling process except for a few parameters like PID. When a process is FORKED in this manner, the child process gets a NEW PID.

Right option is (b) fork

Explanation: A process in UNIX is CREATED using fork() system call. It CREATES an exact COPY of the process that invokes it. Now there will be two processes, ONE parent process and one child process. The process which invokes the fork system call is called parent process and the new process created is called child process.

The correct option is (a) True

The best I can explain: A system call often referred to as kernel call, is a request from a COMPUTER PROGRAM for the SERVICES of the operating system. Basically, to ACCESS the resources or to utilize the services of the operating system, system calls are used by computer programs.