Section 2: system calls
adjtimex, clock_adjtime, ntp_adjtime – tune kernel clock Synopsis#include <sys/timex.h> int adjtimex(struct timex *buf); int clock_adjtime(clockid_t clk_id, struct timex *buf); int ntp_adjtime(struct timex *buf);DescriptionLinux uses David L. Mills’ clock adjustment algorithm (see RFC 5905). The system call adjtimex() reads and optionally sets adjustment parameters for this algorithm. It takes a pointer to a timex structure, updates…
chroot – change root directory Synopsis#include <unistd.h> int chroot(const char *path); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): chroot(): Since glibc 2.2.2: _XOPEN_SOURCE && ! (_POSIX_C_SOURCE >= 200112L) || /* Since glibc 2.20: */ _DEFAULT_SOURCE || /* Glibc versions <= 2.19: */ _BSD_SOURCEBefore glibc 2.2.2: none Descriptionchroot() changes the root directory of the calling process to…
chown, fchown, lchown, fchownat – change ownership of a file Synopsis#include <unistd.h> int chown(const char *pathname, uid_t owner, gid_t group); int fchown(int fd, uid_t owner, gid_t group); int lchown(const char *pathname, uid_t owner, gid_t group); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> int fchownat(int dirfd, const char *pathname, uid_t owner, gid_t group,…
chown, fchown, lchown, fchownat – change ownership of a file Synopsis#include <unistd.h> int chown(const char *pathname, uid_t owner, gid_t group); int fchown(int fd, uid_t owner, gid_t group); int lchown(const char *pathname, uid_t owner, gid_t group); #include <fcntl.h> /* Definition of AT_* constants */ #include <unistd.h> int fchownat(int dirfd, const char *pathname, uid_t owner, gid_t group,…
chmod, fchmod, fchmodat – change permissions of a file Synopsis#include <sys/stat.h> int chmod(const char *pathname, mode_t mode); int fchmod(int fd, mode_t mode); #include <fcntl.h> /* Definition of AT_* constants */ #include <sys/stat.h> int fchmodat(int dirfd, const char *pathname, mode_t mode, int flags);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): fchmod(): Since glibc 2.24: _POSIX_C_SOURCE >= 199309L Glibc…
capget, capset – set/get capabilities of thread(s) Synopsis#include <sys/capability.h> int capget(cap_user_header_t hdrp, cap_user_data_t datap); int capset(cap_user_header_t hdrp, const cap_user_data_t datap); DescriptionThese two system calls are the raw kernel interface for getting and setting thread capabilities. Not only are these system calls specific to Linux, but the kernel API is likely to change and use of…
capget, capset – set/get capabilities of thread(s) Synopsis#include <sys/capability.h> int capget(cap_user_header_t hdrp, cap_user_data_t datap); int capset(cap_user_header_t hdrp, const cap_user_data_t datap); DescriptionThese two system calls are the raw kernel interface for getting and setting thread capabilities. Not only are these system calls specific to Linux, but the kernel API is likely to change and use of…
cacheflush – flush contents of instruction and/or data cache Synopsis#include <asm/cachectl.h> int cacheflush(char *addr, int nbytes, int cache);Note: On some architectures, there is no glibc wrapper for this system call; see NOTES. Descriptioncacheflush() flushes the contents of the indicated cache(s) for the user addresses in the range addr to (addr+nbytes-1). cache may be one of:…
brk, sbrk – change data segment size Synopsis#include <unistd.h> int brk(void *addr); void *sbrk(intptr_t increment); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): brk(), sbrk(): Since glibc 2.19: _DEFAULT_SOURCE || (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200112L)From glibc 2.12 to 2.19: _BSD_SOURCE || _SVID_SOURCE || (_XOPEN_SOURCE >= 500) && ! (_POSIX_C_SOURCE >= 200112L)Before glibc 2.12: _BSD_SOURCE || _SVID_SOURCE || _XOPEN_SOURCE >= 500Descriptionbrk() and sbrk()…
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…
bpf – perform a command on an extended BPF map or program Synopsis#include <linux/bpf.h> int bpf(int cmd, union bpf_attr *attr, unsigned int size);DescriptionThe bpf() system call performs a range of operations related to extended Berkeley Packet Filters. Extended BPF (or eBPF) is similar to the original ("classic") BPF (cBPF) used to filter network packets. For…
bdflush – start, flush, or tune buffer-dirty-flush daemon Synopsis#include <sys/kdaemon.h> int bdflush(int func, long *address); int bdflush(int func, long data);DescriptionNote: Since Linux 2.6, this system call is deprecated and does nothing. It is likely to disappear altogether in a future kernel release. Nowadays, the task performed by bdflush() is handled by the kernel pdflush thread….
sync_file_range – sync a file segment with disk Synopsis#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h> int sync_file_range(int fd, off64_t offset, off64_t nbytes, unsigned int flags);Descriptionsync_file_range() permits fine control when synchronizing the open file referred to by the file descriptor fd with disk. offset is the starting byte of the file range to be synchronized….
posix_fadvise – predeclare an access pattern for file data Synopsis#include <fcntl.h> int posix_fadvise(int fd, off_t offset, off_t len, int advice);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): posix_fadvise(): _POSIX_C_SOURCE >= 200112LDescriptionPrograms can use posix_fadvise() to announce an intention to access file data in a specific pattern in the future, thus allowing the kernel to perform appropriate optimizations….
posix_fadvise – predeclare an access pattern for file data Synopsis#include <fcntl.h> int posix_fadvise(int fd, off_t offset, off_t len, int advice);Feature Test Macro Requirements for glibc (see feature_test_macros(7)): posix_fadvise(): _POSIX_C_SOURCE >= 200112LDescriptionPrograms can use posix_fadvise() to announce an intention to access file data in a specific pattern in the future, thus allowing the kernel to perform appropriate optimizations….
arch_prctl – set architecture-specific thread state Synopsis#include <asm/prctl.h> #include <sys/prctl.h> int arch_prctl(int code, unsigned long addr); int arch_prctl(int code, unsigned long *addr);Descriptionarch_prctl() sets architecture-specific process or thread state. code selects a subfunction and passes argument addr to it; addr is interpreted as either an unsigned long for the "set" operations, or as an unsigned long *,…
alloc_hugepages, free_hugepages – allocate or free huge pages Synopsisvoid *alloc_hugepages(int key, void *addr, size_t len, int prot, int flag); int free_hugepages(void *addr);DescriptionThe system calls alloc_hugepages() and free_hugepages() were introduced in Linux 2.5.36 and removed again in 2.5.54. They existed only on i386 and ia64 (when built with CONFIG_HUGETLB_PAGE). In Linux 2.4.20, the syscall numbers exist,…
alarm – set an alarm clock for delivery of a signal Synopsis#include <unistd.h> unsigned int alarm(unsigned int seconds);Descriptionalarm() arranges for a SIGALRM signal to be delivered to the calling process in seconds seconds. If seconds is zero, any pending alarm is canceled. In any event any previously set alarm() is canceled. Return Valuealarm() returns the…
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…
adjtimex, clock_adjtime, ntp_adjtime – tune kernel clock Synopsis#include <sys/timex.h> int adjtimex(struct timex *buf); int clock_adjtime(clockid_t clk_id, struct timex *buf); int ntp_adjtime(struct timex *buf);DescriptionLinux uses David L. Mills’ clock adjustment algorithm (see RFC 5905). The system call adjtimex() reads and optionally sets adjustment parameters for this algorithm. It takes a pointer to a timex structure, updates…