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A high-level overview of the Linux kernel's system call interface, which handles communication between its various components and the userspace. In computing, a system call (commonly abbreviated to syscall) is the programmatic way in which a computer program requests a service from the operating system [a] on which it is executed.
The write is one of the most basic routines provided by a Unix-like operating system kernel. It writes data from a buffer declared by the user to a given device, such as a file. This is the primary way to output data from a program by directly using a system call. The destination is identified by a numeric code.
For most file systems, a program initializes access to a file in a file system using the open system call. This allocates resources associated to the file (the file descriptor), and returns a handle that the process will use to refer to that file. In some cases the open is performed by the first access.
For a process to start the execution of a different program, it first forks to create a copy of itself. Then, the copy, called the "child process", calls the exec system call to overlay itself with the other program: it ceases execution of its former program in favor of the other. The fork operation creates a separate address space for the ...
The exec calls named ending with an e alter the environment for the new process image by passing a list of environment settings through the envp argument. This argument is an array of character pointers; each element (except for the final element) points to a null-terminated string defining an environment variable .
stat() is a Unix system call that returns file attributes about an inode. The semantics of stat() vary between operating systems. As an example, Unix command ls uses this system call to retrieve information on files that includes: atime: time of last access (ls -lu) mtime: time of last modification (ls -l) ctime: time of last status change (ls -lc)
The file is identified by a file descriptor that is normally obtained from a previous call to open. This system call reads in data in bytes, the number of which is specified by the caller, from the file and stores then into a buffer supplied by the calling process. The read system call takes three arguments: The file descriptor of the file.
A request to the OS is usually in the form of a system call, (i.e. a call from the running process to a function that is part of the OS code). For example, a process might become BLOCKED if it is requesting a file from disk or a saving a section of code or data from memory to a file on disk.