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This command will prompt you to remove Joe's tmp files that are 3 days older. When the -ok option is used with the find command it causes find to execute the rm command once for each /tmp file that is 3 days older. {} can be used as a filename placeholder.

The -ok option with the find command is used to execute a command once for each file that matches the given criteria. This is commonly used in situations such as removing files or renaming files to have a certain extension. The -ok option causes find to ask for each file before removing it.

What is the find command?

The find command is a versatile method for locating files on a file system. The syntax for this command is as follows:

find -

Some of the important criteria are described in the table below:

What are some numeric criteria that the find command uses?

The find command can search your system for files that comply with certain numeric criteria. For

example, -ctime, -atime, -

cmin, -amin, etc. The -ctime and -atime are measured in days and the -cmin and -amin are measures in minutes.

For example:

find /tmp -ctime +10

This command searches for files that are more than 10 days older.

find /tmp -cmin +10

This command searches for files that are more than 10 minutes older.

What is the purpose of using \; at the end of the find command?

The purpose of using \; at the end of the find command is that when find is used with -exec and –ok the find command uses ; as the delimiting character. Unfortunately ; is also a delimiting character for the bash shell so we must prevent bash from interpreting it. When a character is preceded with a backslash (\), bash instructs it literally, so typing \; at the bash command prompt will send ; to find command after bash has done its interpretation.

Answer option A is incorrect. This command will prompt you to remove Joe's tmp files that are 3 minutes older.

Answer options D and B are incorrect. These are the incorrect command syntaxes.

When a user types alias c= 'clear' on the command prompt and presses Enter this will create an alias for the clear command. After creating the alias whenever a user wants to clear the screen, he just needs to type c and then press Enter.

This action will clear the screen. This alias will be lost if a user logs out and logs in again.

What is the alias command?

The alias command is a shortcut name for longer commands. If a command is run often, but it takes a considerable amount of time in typing that command, the time can be reduced by using the alias command.

For example: # alias list= 'ls-la'

This will create an alias called list, which will use the ls command to print a long-style listing of all files in the current directory (the -l gives a long-style list, and the -a shows all files -including hidden files).

Answer options B, C, and A are incorrect. These are incorrect commands and will show error messages on the command prompt.

xinit is a program that allows a user to manually start an X server. The startx script is a front-end for xinit. By default, xinit and

startx start an X server on display :0 and then start an xterm on it. When the xterm terminates, xinit and startx kill the X server. In general,

xinit and startx can start an arbitrary server and run an arbitrary script. Typically, this script runs a number of programs and a window manager. Arguments immediately following the startx command are used to start a client in the same manner as xinit. For example the startx -

- -dpi 100 command starts the xsession with 100 dpi.

The lastb command is used to view failed login attempts on a user account.

What is the lastb command?

The lastb command is used to view bad login attempts. The command searches in reverse order through the database file named /var/adm/btmp in order to display the required information.

Answer option C is incorrect. The lastlog command reports the most recent logins of all users or of a given user.

Answer options A and D are incorrect. There are no such commands as lastw and lastf in Linux.

In order to accomplish the task, you will use the at command. The at command is used to set a specific command or batch file to execute at a certain time.

Syntax:

at [option] schedule time

Several options are used with the at command. Following is a list of some important options:

The atd daemon monitors the queue of the at commands and executes them at a specified time.

Example:

The following command will create a list of jobs to be executed at 8:00 AM on 22nd August 2004.

at 08:00 22.08.2004

at> ls

at> pwd

+

The + key combination is used to end the list of commands.

The jobs can be removed from an at queue by using the atrm command.

Note: The at command cannot schedule recurring jobs.

Answer option C is incorrect. You will not run the crontab command, since it runs a program repeatedly. The crontab command is used to view and edit the crontab files, which are used to organize the cron facility. Each user has access to the

cron facility through a crontab file. Some of the frequently used crontab command options are as follows:

Answer option A is incorrect. In computing, rsync is a software application for Unix systems. It synchronizes files and directories from one location to another while minimizing data transfer using delta encoding. It can copy or display directory contents and copy files, optionally using compression and recursion.

In daemon mode, rsync listens to the default TCP port of 873, serving files in the native rsync protocol or via a remote shell such as RSH or

SSH. In the latter case, the rsync client executable must be installed on both the local and remote hosts.

Answer option D is incorrect. The sync command is used to flush filesystem buffers. It ensures that all disk writes have been completed before the processor is halted or rebooted. Generally, it is preferable to use reboot or halt to shut down a system, as they may perform additional actions such as resynchronizing the hardware clock and flushing internal caches before performing a final sync.