Technical difference between daemon, service and process

Daemons :-  They are the processes which run in the background and are not interactive. They have no controlling terminal. 

                 They perform certain actions at predefined times or in response to certain events. In *nix, the names of daemons end in d.

 

Services - In Windows, daemons are called services.

                   If you're wondering why *nix has a command named service, it is just used to run init scripts (shorthand for initialization scriptrunlevel).

Process - Process is a running program. At a particular instant of time, it can be either running, sleeping, or zombie (completed process, but waiting for it's parent process to pick up the return value).

Courtesy:- http://askubuntu.com/questions/192058/what-is-technical-difference-between-daemon-service-and-process

 

Basic Unix Commands

1) Command : man

Use : This command is used for getting help about UNIX commands.

Syntax : man <command name>

2) Command : grep

Use : This command is used to search for a particular expression in the given input.

Syntax : grep [OPTION]... PATTERN [FILE]...

e.g. : grep <pattern> <file> ---> It can be used to search from lines matching pattern from file.

grep -v <pattern> <file> --> It can be used to search for lines not matching pattern from file.

3) Command : ps

Use : This command is used to see the processes running on the system.

Syntax : ps [options]

e.g. : ps -ef ---> It can used to see the all processes from all users.

ps -ef | grep <process_name> | grep -v grep ---> It can be used to check whether a particular process is running or not.

ps -fu <user_name> ---> It can be used to see all processes started by a particular user.

4) Command : uptime

Use :This command is used check the server/system run duration and number of users currently logged on.

Syntax : uptime

e.g. : user@machine :~$ uptime

17:16:31 up 7:34, 1 user, load average: 0.83, 0.87, 1.03

5) Command : whatis

Use : This command displays manual page descriptions.

Syntax : whatis <command_name>

e.g. : user@machine :~$ whatis firefox

firefox (1) - a free and open source web browser from Mozilla

6) Command : kill

Use : This command send a signal ( default SIGTERM ) to a process.

Syntax : kill <process_id>

e.g. : kill 123 543 2341 3453 ---> Send the default signal, SIGTERM, to all those processes.

7) Command : ls

Use : This command is used to list directory contents.

Syntax : ls [OPTION]... [FILE]...

e.g. : ls -l ---> It shows a log list of all files in the current directory.

8) Command : rm

Use : This command is used to remove files or directories.

Syntax : rm [OPTION]... [FILE]...

e.g. : rm <file_name> ---> It removes the <file_name> .

rm -r <directory_name> --> It removes <directory_name> and all the files/directory inside it.

9) Command : xargs

Use : This command build and execute command lines from standard input.

Syntax : <some_command> | xargs <another_command >

e.g. : ls <file_name_pattern> | xargs rm ---> It is used to delete all files as shown by  output of ls <file_name_pattern> .