Section 2: system calls
add_key – add a key to the kernel’s key management facility Synopsis#include <sys/types.h> #include <keyutils.h> key_serial_t add_key(const char *type, const char *description, const void *payload, size_t plen, key_serial_t keyring);No glibc wrapper is provided for this system call; see NOTES. Descriptionadd_key() creates or updates a key of the given type and description, instantiates it with the…
acct – switch process accounting on or off Synopsis#include <unistd.h> int acct(const char *filename);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): acct(): Since glibc 2.21: _DEFAULT_SOURCE In glibc 2.19 and 2.20: _DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500) Up to and including glibc 2.19: _BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)DescriptionThe acct() system call enables or disables process accounting….
access, faccessat, faccessat2 – check user’s permissions for a file Synopsis#include <unistd.h> int access(const char *pathname, int mode); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> int faccessat(int dirfd, const char *pathname, int mode, int flags); /* But see C library/kernel differences, below */ int faccessat2(int dirfd, const char *pathname, int mode, int…
accept, accept4 – accept a connection on a socket Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); #define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/socket.h> int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);DescriptionThe accept() system call is used with connection-based socket types (SOCK_STREAM, SOCK_SEQPACKET). It…
accept, accept4 – accept a connection on a socket Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); #define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/socket.h> int accept4(int sockfd, struct sockaddr *addr, socklen_t *addrlen, int flags);DescriptionThe accept() system call is used with connection-based socket types (SOCK_STREAM, SOCK_SEQPACKET). It…
listen – listen for connections on a socket Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int listen(int sockfd, int backlog);Descriptionlisten() marks the socket referred to by sockfd as a passive socket, that is, as a socket that will be used to accept incoming connection requests using accept(2). The sockfd argument is a file descriptor…
bind – bind a name to a socket Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int bind(int sockfd, const struct sockaddr *addr, socklen_t addrlen);DescriptionWhen a socket is created with socket(2), it exists in a name space (address family) but has no address assigned to it. bind() assigns the address specified by addr to the…
connect – initiate a connection on a socket Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int connect(int sockfd, const struct sockaddr *addr, socklen_t addrlen);DescriptionThe connect() system call connects the socket referred to by the file descriptor sockfd to the address specified by addr. The addrlen argument specifies the size of addr. The format of…
socket – create an endpoint for communication Synopsis#include <sys/types.h> /* See NOTES */ #include <sys/socket.h> int socket(int domain, int type, int protocol); Descriptionsocket() creates an endpoint for communication and returns a file descriptor that refers to that endpoint. The file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open…
select, pselect, FD_CLR, FD_ISSET, FD_SET, FD_ZERO – synchronous I/O multiplexing Synopsis#include <sys/select.h> int select(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout); void FD_CLR(int fd, fd_set *set); int FD_ISSET(int fd, fd_set *set); void FD_SET(int fd, fd_set *set); void FD_ZERO(fd_set *set); int pselect(int nfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, const struct timespec *timeout,…
getpid, getppid – get process identification Synopsis#include <sys/types.h> #include <unistd.h> pid_t getpid(void); pid_t getppid(void); Descriptiongetpid() returns the process ID (PID) of the calling process. (This is often used by routines that generate unique temporary filenames.) getppid() returns the process ID of the parent of the calling process. This will be either the ID of the…
chdir, fchdir – change working directory Synopsis#include <unistd.h> int chdir(const char *path); int fchdir(int fd); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fchdir(): _XOPEN_SOURCE >= 500 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L || /* Glibc up to and including 2.19: */ _BSD_SOURCEDescriptionchdir() changes the current working directory of the calling process to the directory specified in path. fchdir() is identical to chdir(); the…
execve – execute program Synopsis#include <unistd.h> int execve(const char *pathname, char *const argv[], char *const envp[]); Descriptionexecve() executes the program referred to by pathname. This causes the program that is currently being run by the calling process to be replaced with a new program, with newly initialized stack, heap, and (initialized and uninitialized) data segments….
pipe, pipe2 – create pipe Synopsis#include <unistd.h> /* On Alpha, IA-64, MIPS, SuperH, and SPARC/SPARC64; see NOTES */ struct fd_pair { long fd[2]; }; struct fd_pair pipe(); /* On all other architectures */ int pipe(int pipefd[2]); #define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> /* Obtain O_* constant definitions */ #include <unistd.h> int pipe2(int pipefd[2],…
mmap, munmap – map or unmap files or devices into memory Synopsis#include <sys/mman.h> void *mmap(void *addr, size_t length, int prot, int flags, int fd, off_t offset); int munmap(void *addr, size_t length);See NOTES for information on feature test macro requirements. Descriptionmmap() creates a new mapping in the virtual address space of the calling process. The starting…
fork – create a child process Synopsis#include <sys/types.h> #include <unistd.h> pid_t fork(void); Descriptionfork() creates a new process by duplicating the calling process. The new process is referred to as the child process. The calling process is referred to as the parent process. The child process and the parent process run in separate memory spaces. At…
dup, dup2, dup3 – duplicate a file descriptor Synopsis#include <unistd.h> int dup(int oldfd); int dup2(int oldfd, int newfd); #define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> /* Obtain O_* constant definitions */ #include <unistd.h> int dup3(int oldfd, int newfd, int flags);DescriptionThe dup() system call creates a copy of the file descriptor oldfd, using the lowest-numbered…
close – close a file descriptor Synopsis#include <unistd.h> int close(int fd);Descriptionclose() closes a file descriptor, so that it no longer refers to any file and may be reused. Any record locks (see fcntl(2)) held on the file it was associated with, and owned by the process, are removed (regardless of the file descriptor that was…
write – write to a file descriptor Synopsis#include <unistd.h> ssize_t write(int fd, const void *buf, size_t count); Descriptionwrite() writes up to count bytes from the buffer starting at buf to the file referred to by the file descriptor fd. The number of bytes written may be less than count if, for example, there is insufficient…
read – read from a file descriptor Synopsis#include <unistd.h> ssize_t read(int fd, void *buf, size_t count);Descriptionread() attempts to read up to count bytes from file descriptor fd into the buffer starting at buf. On files that support seeking, the read operation commences at the file offset, and the file offset is incremented by the number…