What are links and symbolic links in UNIX file system?

Unix Interview Questions

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6. What are links and symbolic links in UNIX file system?

A link is a second name (not a file) for a file. Links can be used to assign more than one name to a file, but cannot be used to assign a directory more than one name or link filenames on different computers.
Symbolic link 'is' a file that only contains the name of another file.Operation on the symbolic link is directed to the file pointed by the it.Both the limitations of links are eliminated in symbolic links.
Commands for linking files are:
Link ln filename1 filename2
Symbolic link ln -s filename1 filename2

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Other Interview Questions

• How are devices represented in UNIX?
• What is 'inode'?
• Brief about the directory representation in UNIX
• What are the Unix system calls for I/O?
• How do you change File Access Permissions?
• What are links and symbolic links in UNIX file system?
• What is a FIFO?
• How do you create special files like named pipes and device files?
• Discuss the mount and unmount system calls
• How does the inode map to data block of a file?
• What is a shell?
• Brief about the initial process sequence while the system boots up.
• What are various IDs associated with a process?
• Explain fork() system call.
• Predict the output of the following program code
• Predict the output of the following program code
• List the system calls used for process management:
• How can you get/set an environment variable from a program?:
• How can a parent and child process communicate?
• What is a zombie?
• What are the process states in Unix?
• What Happens when you execute a program?
• What Happens when you execute a command?
• What is a Daemon?
• What is 'ps' command for?
• How would you kill a process?
• What is an advantage of executing a process in background?
• How do you execute one program from within another?
• What is IPC? What are the various schemes available?
• What is the difference between Swapping and Paging?
• What is major difference between the Historic Unix and the new BSD release of Unix System V in terms of Memory Management?
• What is the main goal of the Memory Management?
• What is a Map?
• What scheme does the Kernel in Unix System V follow while choosing a swap device among the multiple swap devices?
• What is a Region?
• What are the events done by the Kernel after a process is being swapped out from the main memory?
• Is the Process before and after the swap are the same? Give reason.
• What do you mean by u-area (user area) or u-block?
• What are the entities that are swapped out of the main memory while swapping the process out of the main memory?
• What is Fork swap?
• What is Expansion swap?
• How the Swapper works?
• What are the processes that are not bothered by the swapper? Give Reason.
• What are the requirements for a swapper to work?
• What are the criteria for choosing a process for swapping into memory from the swap device?
• What are the criteria for choosing a process for swapping out of the memory to the swap device?
• What do you mean by nice value?
• What are conditions on which deadlock can occur while swapping the processes?
• What are conditions for a machine to support Demand Paging?
• What is ‘the principle of locality’?
• What is the working set of a process?
• What is the window of the working set of a process?
• What is called a page fault?
• What are data structures that are used for Demand Paging?
• What are the bits that support the demand paging?
• How the Kernel handles the fork() system call in traditional Unix and in the System V Unix, while swapping?
• Difference between the fork() and vfork() system call?
• What is BSS(Block Started by Symbol)?
• What is Page-Stealer process?
• Name two paging states for a page in memory?
• What are the phases of swapping a page from the memory?
• What is page fault? Its types?
• In what way the Fault Handlers and the Interrupt handlers are different?
• What is validity fault?
• What does the swapping system do if it identifies the illegal page for swapping?
• What are states that the page can be in, after causing a page fault?
• In what way the validity fault handler concludes?
• At what mode the fault handler executes?
• What do you mean by the protection fault?
• How the Kernel handles the copy on write bit of a page, when the bit is set?
• For which kind of fault the page is checked first?
• In what way the protection fault handler concludes?
• How the Kernel handles both the page stealer and the fault handler?
• Explain different types of Unix systems.
• 73. Explain kernal and shell.
• 74. What is ex and vi ?
• Which are typical system directories below the root directory?
• Construct pipes to execute the following jobs.
• Explain the following commands.
• What is the significance of the “tee” command?
• What does the command “ $who | sort –logfile > newfile” do?
• What does the command “$ls | wc –l > file1” do?
• Which of the following commands is not a filter man , (b) cat , (c) pg , (d) head
• How is the command “$cat file2 “ different from “$cat >file2 and >> redirection operators ?
• Explain the steps that a shell follows while processing a command.
• What difference between cmp and diff commands?
• What is the use of ‘grep’ command?
• What is the difference between cat and more command?
• Write a command to kill the last background job?
• Which command is used to delete all files in the current directory and all its sub-directories?
• Write a command to display a file’s contents in various formats?
• What will the following command do?
• Is it possible to create new a file system in UNIX?
• Is it possible to restrict incoming message?
• What is the use of the command "ls -x chapter[1-5]"
• Is ‘du’ a command? If so, what is its use?
• Is it possible to count number char, line in a file; if so, How?
• Name the data structure used to maintain file identification?
• How many prompts are available in a UNIX system?
• How does the kernel differentiate device files and ordinary files?
• How to switch to a super user status to gain privileges?
• What are shell variables?
• What is redirection?
• How to terminate a process which is running and the specialty on command kill 0?
• What is a pipe and give an example?
• Explain kill() and its possible return values.