Unix OS Interview Questions and Answers - DoAnswers.com

An operating system co-created by AT&T researchers Dennis Ritchie and Ken Thompson. Unix is well known for its relative hardware independence and portable application interfaces. Lots of big companies are using Unix servers for its reliability and scalability. Some of the popular Unix flavours are: Linux, Solaris, HP-UX, AIX, etc. The Open Group holds the definition of what a UNIX system is and its associated trademark in trust for the industry. The UNIX* operating system was designed to let a number of programmers access the computer at the same time and share its resources. The operating system coordinates the use of the computer's resources, allowing one person, for example, to run a spell check program while another creates a document, lets another edit a document while another creates graphics, and lets another user format a document -- all at the same time, with each user oblivious to the activities of the others. The operating system controls all of the commands from all of the keyboards and all of the data being generated, and permits each user to believe he or she is the only person working on the computer. This real-time sharing of resources make UNIX one of the most powerful operating systems ever.

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11. Display the last newly appending lines of a file during appendingdata to the same file by some processes ?

tail .f Debug.logHere tail shows the newly appended data into Debug.log by some processes/user.

ipc mechanisms are mianly 5 types 1.pipes:it is related data only send from one pipe output is giving to another pipe input to share resouses pipe are used drawback:itis only related process only communicated 2.message queues:message queues are un related process are also communicate with message queues drawback:user dont know which process curently works share memory:memory shared in distributed systems some memory wants to share some files that time it is use full semaphores semaphore is integer type and in semaphore resourses give coding like negetive value means process are wants to use perticular resource waiting only and 0 means no process is waiting and 1 means one resource is free and sockets:sockets also ipc it is comunicate clients and server with socket system calls connection oriented and connection less also PIPE: Only two related (eg: parent & child) processess can be communicated. Data reading would be first in first out manner. Named PIPE or FIFO : Only two processes (can be related or unrelated) can communicate. Data read from FIFO is first in first out manner. Message Queues: Any number of processes can read/write from/to the queue. Data can be read selectively. (need not be in FIFO manner) Shared Memory: Part of process's memory is shared to other processes. other processes can read or write into this shared memory area based on the permissions. Accessing Shared memory is faster than any other IPC mechanism as this does not involve any kernel level switching(Shared memory resides on user memory area). Semaphore: Semaphores are used for process synchronisation. This can't be used for bulk data transfer between processes.