Section 2: system calls
recv, recvfrom, recvmsg – receive a message from a socket Synopsis#include <sys/types.h> #include <sys/socket.h> ssize_t recv(int sockfd, void *buf, size_t len, int flags); ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen); ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);DescriptionThe recv(), recvfrom(), and recvmsg() calls are used to receive messages…
recvmmsg – receive multiple messages on a socket Synopsis#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/socket.h> int recvmmsg(int sockfd, struct mmsghdr *msgvec, unsigned int vlen, int flags, struct timespec *timeout);DescriptionThe recvmmsg() system call is an extension of recvmsg(2) that allows the caller to receive multiple messages from a socket using a single system call. (This…
recv, recvfrom, recvmsg – receive a message from a socket Synopsis#include <sys/types.h> #include <sys/socket.h> ssize_t recv(int sockfd, void *buf, size_t len, int flags); ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen); ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);DescriptionThe recv(), recvfrom(), and recvmsg() calls are used to receive messages…
recv, recvfrom, recvmsg – receive a message from a socket Synopsis#include <sys/types.h> #include <sys/socket.h> ssize_t recv(int sockfd, void *buf, size_t len, int flags); ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags, struct sockaddr *src_addr, socklen_t *addrlen); ssize_t recvmsg(int sockfd, struct msghdr *msg, int flags);DescriptionThe recv(), recvfrom(), and recvmsg() calls are used to receive messages…
reboot – reboot or enable/disable Ctrl-Alt-Del Synopsis/* Since kernel version 2.1.30 there are symbolic names LINUX_REBOOT_* for the constants and a fourth argument to the call: */ #include <unistd.h> #include <linux/reboot.h> int reboot(int magic, int magic2, int cmd, void *arg); /* Under glibc and most alternative libc’s (including uclibc, dietlibc, musl and a few others), some…
readv, writev, preadv, pwritev, preadv2, pwritev2 – read or write data into multiple buffers Synopsis#include <sys/uio.h> ssize_t readv(int fd, const struct iovec *iov, int iovcnt); ssize_t writev(int fd, const struct iovec *iov, int iovcnt); ssize_t preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset); ssize_t pwritev(int fd, const struct iovec *iov, int iovcnt, off_t…
readlink, readlinkat – read value of a symbolic link Synopsis#include <unistd.h> ssize_t readlink(const char *pathname, char *buf, size_t bufsiz); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> ssize_t readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): readlink(): _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L || /* Glibc versions <= 2.19: */ _BSD_SOURCE readlinkat(): Since glibc…
readlink, readlinkat – read value of a symbolic link Synopsis#include <unistd.h> ssize_t readlink(const char *pathname, char *buf, size_t bufsiz); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> ssize_t readlinkat(int dirfd, const char *pathname, char *buf, size_t bufsiz);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): readlink(): _XOPEN_SOURCE >= 500 || _POSIX_C_SOURCE >= 200112L || /* Glibc versions <= 2.19: */ _BSD_SOURCE readlinkat(): Since glibc…
readdir – read directory entry Synopsisint readdir(unsigned int fd, struct old_linux_dirent *dirp, unsigned int count);Note: There is no glibc wrapper for this system call; see NOTES. DescriptionThis is not the function you are interested in. Look at readdir(3) for the POSIX conforming C library interface. This page documents the bare kernel system call interface, which…
readahead – initiate file readahead into page cache Synopsis#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> ssize_t readahead(int fd, off64_t offset, size_t count);Descriptionreadahead() initiates readahead on a file so that subsequent reads from that file will be satisfied from the cache, and not block on disk I/O (assuming the readahead was initiated early enough and…
quotactl – manipulate disk quotas Synopsis#include <sys/quota.h> #include <xfs/xqm.h> /* for XFS quotas */ int quotactl(int cmd, const char *special, int id, caddr_t addr);DescriptionThe quota system can be used to set per-user, per-group, and per-project limits on the amount of disk space used on a filesystem. For each user and/or group, a soft limit and…
query_module – query the kernel for various bits pertaining to modules Synopsis#include <linux/module.h> int query_module(const char *name, int which, void *buf, size_t bufsize, size_t *ret);Note: No declaration of this system call is provided in glibc headers; see NOTES. DescriptionNote: This system call is present only in kernels before Linux 2.6. query_module() requests information from the…
readv, writev, preadv, pwritev, preadv2, pwritev2 – read or write data into multiple buffers Synopsis#include <sys/uio.h> ssize_t readv(int fd, const struct iovec *iov, int iovcnt); ssize_t writev(int fd, const struct iovec *iov, int iovcnt); ssize_t preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset); ssize_t pwritev(int fd, const struct iovec *iov, int iovcnt, off_t…
readv, writev, preadv, pwritev, preadv2, pwritev2 – read or write data into multiple buffers Synopsis#include <sys/uio.h> ssize_t readv(int fd, const struct iovec *iov, int iovcnt); ssize_t writev(int fd, const struct iovec *iov, int iovcnt); ssize_t preadv(int fd, const struct iovec *iov, int iovcnt, off_t offset); ssize_t pwritev(int fd, const struct iovec *iov, int iovcnt, off_t…
pread, pwrite – read from or write to a file descriptor at a given offset Synopsis#include <unistd.h> ssize_t pread(int fd, void *buf, size_t count, off_t offset); ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): pread(), pwrite(): _XOPEN_SOURCE >= 500 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809LDescriptionpread() reads…
pread, pwrite – read from or write to a file descriptor at a given offset Synopsis#include <unistd.h> ssize_t pread(int fd, void *buf, size_t count, off_t offset); ssize_t pwrite(int fd, const void *buf, size_t count, off_t offset); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): pread(), pwrite(): _XOPEN_SOURCE >= 500 || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809LDescriptionpread() reads…
afs_syscall, break, fattach, fdetach, ftime, getmsg, getpmsg, gtty, isastream, lock, madvise1, mpx, prof, profil, putmsg, putpmsg, security, stty, tuxcall, ulimit, vserver – unimplemented system calls SynopsisUnimplemented system calls. DescriptionThese system calls are not implemented in the Linux kernel. Return ValueThese system calls always return -1 and set errno to ENOSYS. NotesNote that ftime(3), profil(3), and…
afs_syscall, break, fattach, fdetach, ftime, getmsg, getpmsg, gtty, isastream, lock, madvise1, mpx, prof, profil, putmsg, putpmsg, security, stty, tuxcall, ulimit, vserver – unimplemented system calls SynopsisUnimplemented system calls. DescriptionThese system calls are not implemented in the Linux kernel. Return ValueThese system calls always return -1 and set errno to ENOSYS. NotesNote that ftime(3), profil(3), and…
ptrace – process trace Synopsis#include <sys/ptrace.h> long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data);DescriptionThe ptrace() system call provides a means by which one process (the "tracer") may observe and control the execution of another process (the "tracee"), and examine and change the tracee’s memory and registers. It is primarily used to implement breakpoint…
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,…