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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.
For this reason exec is sometimes described as a collection of functions. Standard names of such functions in C are execl, execle, execlp, execv, execve, and execvp (see below), but not "exec" itself. The Linux kernel has one corresponding system call named "execve", whereas all aforementioned functions are user-space wrappers around it.
In the Linux kernel, various subsystems, such as the Direct Rendering Manager (DRM), define their own system calls, all of which are part of the system call interface. Various issues with the organization of the Linux kernel system calls are being publicly discussed. Issues have been pointed out by Andy Lutomirski, Michael Kerrisk and others.
These functions may be implemented as library routines in terms of fork, as is done in Linux, [12] or in terms of vfork for better performance, as is done in Solaris, [12] [13] but the POSIX specification notes that they were "designed as kernel operations", especially for operating systems running on constrained hardware and real-time systems ...
A kernel that provides several hundred system calls may provide several thousand ioctl calls. Though the interface to ioctl calls appears somewhat different from conventional system calls, there is in practice little difference between an ioctl call and a system call; an ioctl call is simply a system call with a different dispatching mechanism.
stat command line. 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:
In modern POSIX compliant operating systems, a program that needs to access data from a file stored in a file system uses the read system call.The file is identified by a file descriptor that is normally obtained from a previous call to open.