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Right answer is (d) read, write, close

The BEST I can explain: A FILE descriptor is an integer which is allocated when a file is opened. It is used by all system calls that PERFORM some operations on file -LIKE read, write, close, lseek.

The correct choice is (b) False

Easy EXPLANATION: System calls are built into the kernel, but LIBRARY FUNCTIONS are built on top of them. When a system call is invoked, the pre-processor SWITCHES to kernel mode and returns to the user mode when the call COMPLETES.

Correct option is (b) utime

Easiest explanation: utime SYSTEM call is used to CHANGE a file’s modification and ACCESS TIMES.

Right answer is (a) True

To explain I would say: chmod and fchmod calls are USED for CHANGING the file PERMISSIONS. Chmod uses pathname for IDENTIFYING a file while fchmod uses the file descriptor.

Right choice is (d) R_OK, W_OK, X_OK

To explain: By using the ACCESS system call, we can CHECK the FILE’s access RIGHTS. We’ve to specify one of the FOLLOWING four values to define the permission which is needed to be tested.

Right option is (B) S_ISDIR

Explanation: The S_ISDIR MACRO RETURNS TRUE if the file type is a directory. The S_ISREG returns true if the file type is REGULAR.

Correct choice is (a) True

The BEST EXPLANATION: All UNIX systems provide a SET of macros beginning with S_IF (often called S_IFxxx macros) that provide us with a function of checking the file type. But modern UNIX system PERFORMS this task in a more simplified manner using S_ISxxx macros.

Correct CHOICE is (b) rename

The best I can explain: The rename call is USED for renaming any TYPE of FILE. It can rename a file, a directory or a SYMBOLIC link.

Right choice is (c) unlink

Explanation: The unlink system call removes the directory entry for the FILE (the ARGUMENT) and decrements the LINK count in its INODE by ONE.

Correct option is (B) link, symlink

To explain: UNLIKE the ln command which CREATES both hard and symbolic LINKS, the system call library has two separate functions, link and symlink for these tasks.

Right CHOICE is (a) MKNOD

The EXPLANATION is: A superuser can use the mknod system call to create a directory but a NON privileged USER has to use the mkdir call.

The correct OPTION is (a) True

The EXPLANATION: Directories are also files, and they can also be written, read and opened in the same way as regular files. We can USE open, close and read SYSTEM calls for PERFORMING these tasks.

Correct answer is (d) mkdir and rmdir

The explanation: A NON privileged user uses mkdir and rmdir calls for creating and REMOVING DIRECTORIES respectively.

Right option is (d) chdir and fchdir

Explanation: There are two SYSTEM CALLS that PERFORM the action of cd COMMAND. They are chdir and fchdir which uses pathname and a file descriptor RESPECTIVELY as an argument.

The correct choice is (a) INODE table

The explanation is: The file table contains a POINTER to the vnode table, which is the third table in the scheme. It is also CALLED as inode table. This table contains all the information present in the inode except that this structure is MAINTAINED in MEMORY.

Correct answer is (d) mode of opening, STATUS flags, offset printer and REFERENCE count

Easy EXPLANATION: Every entry in the FILE descriptor table points to a file table. This table contains all the data which is RELEVANT to an opened file.

Correct choice is (a) True

To EXPLAIN I would SAY: The file DESCRIPTOR table contains all allocated file descriptors for a process. Each ENTRY POINTS to the file table. The file descriptor is stored along with a flag in this table.

Right OPTION is (c) EIOR

The best I can explain: EPERM displays not a super user (errno 1), ENDENT displays no such FILE or directory (errno 2), EEXIST displays file exist (errno 17).

Correct choice is (b) ENDENT

To EXPLAIN: The symbolic constant for errno 2 is ENDENT. It DISPLAYS the message “no such file and DIRECTORY”.

The correct answer is (B) no such FILE and directory

For explanation: The ERRNO 13 DISPLAYS the message “permission denied”. The SYMBOLIC constant for this errno is EACCES.

The CORRECT option is (a) strerror

Explanation: The library FUNCTION strerror, USES the error NUMBER as argument and returns a pointer to the STRING representing the error.

Correct option is (a) pathname, file descriptor

Explanation: The truncate and ftruncate CALLS can truncate a file to any LENGTH. truncate NEEDS the pathname of the file as an argument but ftruncate WORKS with the file descriptor.

Right choice is (d) truncate and ftruncate

The BEST I can explain: The truncate and ftruncate calls can truncate a FILE to any LENGTH. These calls are often used in COMBINATION with lseek to overwrite a certain segment of a file.

Correct CHOICE is (b) SEEK_END

The best I can explain: The offset SIGNIFIES the position of the offset pointer which can TAKE one of these three VALUES:

Right answer is (d) lseek

The explanation is: The lseek system call MOVES the file OFFSET POINTER to a specified point. It doesn’t do any physical I/O rather it determines the position in the file where the next I/O OPERATION will TAKE place.

The CORRECT choice is (d) if disk fills up while WRITE is in progress and if the file size EXCEEDS

To explain I would say: write system call RETURNS the number of characters WRITTEN. However, it will return -1 if if disk fills up while write is in progress or if the file size exceeds the system’s limit.

Correct option is (B) write

The explanation is: write system call is required for WRITING to a FILE which has previously been opened with the open system call. write system call RETURNS the number of characters written.

Correct option is (c) CLOSE

To explain I would say: A PROGRAM automatically closes all open files before TERMINATION, but it’s a GOOD practice to close them explicitly. The close system CALL is used for closing a file.

int close (int fd)

The correct answer is (c) char

Explanation: OPEN returns the FILE descriptor as an INT. This is the lowest number available for allocation and is used as an ARGUMENT by the other four calls (read, WRITE, close, lseek).

The correct ANSWER is (C) open

Best explanation: To read or write to a FILE, we first need to open it. For this purpose, open SYSTEM call is USED. Open has two forms ; the first forms assumes that the file already exists and the second form creates the file if it doesn’t.

Right option is (b) 3

For EXPLANATION: There are THREE modes of opening a FILE, out of which only one MODE is required to be specified while opening the file. The three modes are, O_RDONLY, O_WRONLY, O_RDWR.

Correct answer is (c) read

The best explanation: The STANDARD C library offers a set of separate FUNCTIONS to read a block of data. For example, to read a block of data fread is used, for reading a line FGETS is used and for reading a character fgetc is used. All these functions invoke the SYSTEM CALL -read, which is available for reading input.

Correct option is (a) CHMOD

Explanation: Many commands and system CALLS SHARE the same NAMES. For example, the chmod command invokes the chmod system call.

Correct answer is (a) SET of system CALLS

For explanation: As we know that, all UNIX and LINUX SYSTEMS have one THING in common; they use the same set of system calls.

Correct answer is (a) user

For explanation I would SAY: When we execute a C PROGRAM, the CPU runs in user mode. It remains it this particular mode until a system CALL is invoked.