Section 2: system calls
NAME recv, recvfrom, recvmsg – receive a message from a socket SYNOPSIS #include <sys/socket.h> #include <sys/types.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); DESCRIPTION The recv(), recvfrom(), and recvmsg() calls are…
NAME 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); DESCRIPTION The recvmmsg() system call is an extension of recvmsg(2) that allows the caller to receive multiple messages from a socket using a…
NAME recv, recvfrom, recvmsg – receive a message from a socket SYNOPSIS #include <sys/socket.h> #include <sys/types.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); DESCRIPTION The recv(), recvfrom(), and recvmsg() calls are…
NAME recv, recvfrom, recvmsg – receive a message from a socket SYNOPSIS #include <sys/socket.h> #include <sys/types.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); DESCRIPTION The recv(), recvfrom(), and recvmsg() calls are…
NAME 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…
NAME 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…
NAME 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…
NAME 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…
NAME readdir – read directory entry SYNOPSIS int readdir(unsigned int fd, struct old_linux_dirent *dirp, unsigned int count); Note: There is no glibc wrapper for this system call; see NOTES. DESCRIPTION This 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…
NAME 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); DESCRIPTION readahead() 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…
NAME 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); DESCRIPTION The 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,…
NAME 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. DESCRIPTION Note: This system call is present only in kernels before Linux 2.6. query_module()…
NAME 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…
NAME 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…
NAME 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: */…
NAME 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: */…
NAME 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 SYNOPSIS Unimplemented system calls. DESCRIPTION These system calls are not implemented in the Linux kernel. RETURN VALUE These system calls always return -1 and set errno to ENOSYS. NOTES…
NAME 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 SYNOPSIS Unimplemented system calls. DESCRIPTION These system calls are not implemented in the Linux kernel. RETURN VALUE These system calls always return -1 and set errno to ENOSYS. NOTES…
NAME ptrace – process trace SYNOPSIS #include <sys/ptrace.h> long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data); DESCRIPTION The 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…
NAME 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…