Kernel is used in UNIX like systems and is considered to be the heart of the operating system. It is responsible for communication between hardware and software components. It is primarily used for managing the systems resources as well.
Kernel Activities:
- The Kernel task manager allows tasks to run concurrently.
- Managing the computer resources: Kernel allows the other programs to run and use the resources
- Resources include i/o devices, CPU, memory.
- Kernel is responsible for Process management. It allows multiple processes to run simultaneously allowing user to multitask.
- Kernel has an access to the systems memory and allows the processes to access the memory when required.
- Processes may also need to access the devices attached to the system. Kernel assists the processes in doing so.
- For the processes to access and make use of these services, system calls are used.
Linux shell is a user interface used for executing the commands. Shell is a program the user uses for executing the commands. In UNIX, any program can be the users shell. Shell categories in Linux are:
Bourne shell compatible, C shell compatible, nontraditional, and historical.
A shell script, as the name suggests, is a script written
for the shell. Script here means a programming language used to control
the application. The shell script allows different commands entered in
the shell to be executed. Shell script is easy to
debug, quicker as compared to writing big programs. However
the execution speed is slow because it launches a new process for every
shell command executed. Examples of commands are cp, cn, cd.
What are Pipes? Explain uses of pipes.
A pipe is a chain of processes so that output of one process (stdout) is fed an input (stdin) to another. UNIX shell has a special syntax for creation of pipelines. The commands are written in sequence separated by |. Different filters are used for Pipes like AWK, GREP.
e.g. sort file | lpr ( sort the file and send it to printer)
Uses of Pipe
Several powerful functions can be in a single statement
Streams of processes can be redirected to user specified
locations using >
Explain trap command; shift Command, getopts command of linux.
Trap command: controls the action to be taken by the shell when a signal is received.
Trap [OPTIONS] [ [arg] signspec..]
Arg is the action to be taken or executed on receiving
a signal specified in signspec.
e.g. trap “rm $FILE; exit” // exit (signal) and remove
file (action)
Shift Command: Using shift command, command line arguments can be accessed.
The command causes the positional parameters shift to the left. Shift [n] where n defaults to 1. It is useful when several parameters need to be tested.
Getopts command: this command is used to parse arguments passed. It examines the next command line argument and determines whether it is a valid option
Getopts {optstring} {variable1}. Here, optsring contains
letters to be recognized if a letter is followed by a colon, an argument
should be specified. E.g (whether the argument begins with a minus sign
and is followed by any single letter contained
inside options ) If not, diagnostic messages are shown.
It is usually executed inside a loop.
What Stateless Linux server? What feature it offers?
A stateless Linux server is a centralized server in which no state exists on the single workstations. There may be scenarios when a state of a partilcuar system is meaningful (A snap shot is taken then) and the user wants all the other machines to be in that state. This is where the stateless Linux server comes into picture.
Features:
- It stores the prototypes of every machine
- It stores snapshots taken for those systems
- It stores home directories for those systems
- Uses LDAP containing information of all systems to assist in finding out which snapshot (of state) should be running on which system.
