System Calls

Process Control:

• fork() - Creates a new child process by duplicating the calling process.
• execve() - Replaces the current process image with a new program.
• exit() - Terminates the calling process.
• wait(), waitpid() - Waits for state changes in a child process.
• getpid(), getppid() - Returns the process ID of the calling or parent process.
• getuid(), geteuid() - Gets the real and effective user ID of the calling process.
• getgid(), getegid() - Gets the real and effective group ID.
• setuid(), seteuid() - Sets the user ID of the calling process.
• setgid(), setegid() - Sets the group ID.
• kill() - Sends a signal to a process or group of processes.
• nice() - Changes the scheduling priority of the process.
• ptrace() - Provides processes with the ability to observe and control other processes.

File Operations

• open(), openat() - Opens a file descriptor for a file.
• close() - Closes an open file descriptor.
• read() - Reads data from a file descriptor.
• write() - Writes data to a file descriptor.
• lseek() - Repositions the read/write file offset.
• pread(), pwrite() - Reads or writes data at a given offset without changing the file offset.
• stat(), fstat(), lstat() - Retrieves information about a file.
• chmod(), fchmod() - Changes the permissions of a file.
• chown(), fchown() - Changes the ownership of a file.
• unlink(), unlinkat() - Deletes a name from the filesystem.
• rename(), renameat() - Renames a file or directory.
• mkdir(), mkdirat() - Creates a new directory.
• rmdir() - Removes a directory.
• link(), symlink(), readlink() - Creates or reads symbolic and hard links.
• fsync(), fdatasync() - Synchronizes a file’s in-memory state with storage device.
• dup(), dup2(), dup3() - Duplicates a file descriptor.
• fcntl() - Performs operations on file descriptors.
• ioctl() - Device-specific input/output control operations.

Directory Operations

• opendir(), fdopendir() - Opens a directory stream.
• readdir() - Reads a directory entry.
• closedir() - Closes a directory stream.
• rewinddir() - Resets the position of the directory stream.
• scandir() - Scans a directory for matching entries.
• chdir() - Changes the current working directory.
• getcwd() - Retrieves the current working directory path.

Memory Management

• brk(), sbrk() - Changes the end of the data segment (allocates/deallocates memory).
• mmap(), munmap() - Maps or unmaps files or devices into memory.
• mprotect() - Changes protection on a region of memory.
• mlock(), munlock() - Locks or unlocks memory in RAM.
• shmat(), shmdt() - Attaches or detaches shared memory segments.

Inter-Process Communication (IPC)

Pipes and FIFOs

• pipe(), pipe2() - Creates a unidirectional data channel (pipe).
• mkfifo(), mkfifoat() - Creates a named pipe (FIFO).

Message Queues

• msgget() - Creates or accesses a message queue.
• msgsnd() - Sends a message to a queue.
• msgrcv() - Receives a message from a queue.
• msgctl() - Performs control operations on a message queue.

Semaphores

• semget() - Creates or accesses a semaphore set.
• semop() - Performs operations on semaphores.
• semctl() - Performs control operations on a semaphore set.

Shared Memory

• shmget() - Allocates shared memory.
• shmat(), shmdt() - Attaches/detaches shared memory.
• shmctl() - Controls shared memory operations.

Sockets

• socket() - Creates an endpoint for communication.
• bind() - Binds a name to a socket.
• listen() - Listens for socket connections.
• accept(), accept4() - Accepts a socket connection.
• connect() - Initiates a connection on a socket.
• send(), recv() - Sends/receives messages on a socket.
• sendto(), recvfrom() - Sends/receives messages to/from a socket.
• socketpair() - Creates a pair of connected sockets.

Signals

• signal(), sigaction() - Installs a signal handler.
• raise() - Sends a signal to the calling process.
• kill() - Sends a signal to a process.
• sigprocmask() - Examines or changes blocked signals.
• sigpending() - Checks for pending signals.
• sigsuspend() - Waits for a signal.
• sigwait() - Waits for signals in a set.

Timers and Clocks

• time() - Returns the current time.
• gettimeofday(), settimeofday() - Gets/sets the system time.
• clock_gettime(), clock_settime() - Accesses high-resolution clocks.
• nanosleep() - Suspends execution for a specified time.
• alarm() - Schedules a SIGALRM signal.
• setitimer(), getitimer() - Sets or gets the value of an interval timer.
• timer_create(), timer_delete(), timer_settime(), timer_gettime() - Manages POSIX timers.

Resource Management

• getrlimit(), setrlimit() - Gets or sets resource limits.
• getrusage() - Returns resource usage measures.

User and Group Management

• getpwnam(), getpwuid() - Retrieves password file entries.
• getgrnam(), getgrgid() - Retrieves group database entries.

Process Scheduling

• sched_getscheduler(), sched_setscheduler() - Gets or sets the scheduling policy.
• sched_getparam(), sched_setparam() - Gets or sets scheduling parameters.
• sched_yield() - Yields the processor.
• sched_get_priority_max(), sched_get_priority_min() - Gets priority limits.

Miscellaneous

• uname() - Gets system information.
• sysinfo() - Retrieves system statistics.
• ptrace() - Traces processes (used for debugging).
• sysctl() - Reads or writes system parameters.
• umask() - Sets file mode creation mask.

Standard Library Functions (glibc)

String Manipulation

• strlen(), strnlen() - Calculates the length of a string.
• strcpy(), strncpy() - Copies strings.
• strcat(), strncat() - Concatenates strings.
• strcmp(), strncmp() - Compares strings.
• strchr(), strrchr() - Locates characters in a string.
• strstr(), strcasestr() - Finds a substring.
• sprintf(), snprintf() - Writes formatted output to a string.
• sscanf() - Reads formatted input from a string.

Memory Functions

• malloc(), calloc(), realloc(), free() - Allocates and manages dynamic memory.
• memcpy(), memmove() - Copies memory areas.
• memset() - Fills memory with a constant byte.
• memcmp() - Compares memory areas.

Input/Output

• printf(), fprintf() - Prints formatted output.
• scanf(), fscanf() - Reads formatted input.
• getc(), fgetc(), getchar() - Reads a character from a file or stdin.
• putc(), fputc(), putchar() - Writes a character to a file or stdout.
• fgets() - Reads a string from a file.
• fputs(), puts() - Writes a string to a file or stdout.
• fopen(), freopen(), fdopen() - Opens a file stream.
• fclose() - Closes a file stream.
• fread(), fwrite() - Reads or writes data to/from a file.
• fseek(), ftell() - Repositions or obtains the position of the file pointer.
• fflush() - Flushes a file stream.

Mathematical Functions

• abs(), labs(), llabs() - Computes absolute value.
• ceil(), floor() - Rounds a number up or down.
• sqrt(), cbrt() - Calculates square or cube roots.
• pow(), exp(), log(), log10() - Exponential and logarithmic functions.
• sin(), cos(), tan() - Trigonometric functions.
• asin(), acos(), atan(), atan2() - Inverse trigonometric functions.

System Utilities

• system() - Executes a shell command.
• getenv(), putenv(), setenv(), unsetenv() - Gets or sets environment variables.
• getopt(), getopt_long() - Parses command-line options.
• exit(), _exit(), atexit() - Exits a program and registers functions to be called at exit.
• qsort(), bsearch() - Sorts and searches arrays.

Date and Time

• time() - Gets the current time.
• ctime(), asctime() - Converts time to a string representation.
• localtime(), gmtime() - Converts time to broken-down time.
• mktime() - Converts broken-down time to time since the Epoch.
• strftime(), strptime() - Formats and parses date and time.

POSIX Threads (pthread)

Thread Management

• pthread_create() - Creates a new thread.
• pthread_exit() - Terminates the calling thread.
• pthread_join() - Waits for thread termination.
• pthread_detach() - Marks a thread for detachment.
• pthread_self() - Returns the calling thread’s ID.
• pthread_equal() - Compares thread IDs.
• pthread_cancel() - Sends a cancellation request to a thread.
• pthread_setcancelstate(), pthread_setcanceltype() - Sets thread cancellation state and type.

Thread Attributes

• pthread_attr_init(), pthread_attr_destroy() - Initializes/destroys thread attributes object.
• pthread_attr_setdetachstate(), pthread_attr_getdetachstate() - Sets/gets detach state.
• pthread_attr_setschedpolicy(), pthread_attr_getschedpolicy() - Sets/gets scheduling policy.
• pthread_attr_setschedparam(), pthread_attr_getschedparam() - Sets/gets scheduling parameters.

Mutexes

• pthread_mutex_init(), pthread_mutex_destroy() - Initializes/destroys a mutex.
• pthread_mutex_lock(), pthread_mutex_trylock(), pthread_mutex_unlock() - Locks/unlocks a mutex.
• pthread_mutexattr_init(), pthread_mutexattr_destroy() - Initializes/destroys mutex attribute object.
• pthread_mutexattr_settype(), pthread_mutexattr_gettype() - Sets/gets the mutex type.

Condition Variables

• pthread_cond_init(), pthread_cond_destroy() - Initializes/destroys a condition variable.
• pthread_cond_wait(), pthread_cond_timedwait() - Waits on a condition variable.
• pthread_cond_signal(), pthread_cond_broadcast() - Signals a condition variable.

Read-Write Locks

• pthread_rwlock_init(), pthread_rwlock_destroy() - Initializes/destroys a read-write lock.
• pthread_rwlock_rdlock(), pthread_rwlock_wrlock(), pthread_rwlock_unlock() - Locks/unlocks a read-write lock.

Thread-Specific Data (TSD)

• pthread_key_create(), pthread_key_delete() - Creates/deletes a thread-specific data key.
• pthread_setspecific(), pthread_getspecific() - Sets/gets thread-specific data.

Barriers

• pthread_barrier_init(), pthread_barrier_destroy() - Initializes/destroys a barrier.
• pthread_barrier_wait() - Synchronizes threads at a barrier.

Networking (Sockets API)

Socket Creation and Configuration

• socket() - Creates a socket.
• socketpair() - Creates a pair of connected sockets.
• bind() - Binds a socket to an address.
• listen() - Listens for connections on a socket.
• accept(), accept4() - Accepts a connection on a socket.
• connect() - Initiates a connection on a socket.
• getsockname(), getpeername() - Gets the local or remote address of a socket.
• getsockopt(), setsockopt() - Gets/sets options on sockets.

Data Transmission

• send(), recv() - Sends/receives data on a socket.
• sendto(), recvfrom() - Sends/receives messages with addresses.
• sendmsg(), recvmsg() - Sends/receives messages with ancillary data.
• shutdown() - Disables sends or receives on a socket.

Address and Name Resolution

• gethostbyname(), gethostbyaddr() - Gets host entry by name/address.
• getaddrinfo(), freeaddrinfo() - Translates hostnames and service names to socket addresses.
• inet_aton(), inet_addr(), inet_ntoa(), inet_ntop(), inet_pton() - Converts IP addresses between binary and text.

Network Byte Order Conversion

• htons(), htonl() - Converts values from host to network byte order.
• ntohs(), ntohl() - Converts values from network to host byte order.

Inter-Process Communication (Advanced IPC)

Event Mechanisms

• select(), pselect() - Monitors multiple file descriptors.
• poll(), ppoll() - Waits for events on file descriptors.
• epoll_create(), epoll_ctl(), epoll_wait(), epoll_pwait() - Scalable I/O event notification mechanisms.

Inotify (Filesystem Event Monitoring)

• inotify_init(), inotify_init1() - Initializes inotify instance.
• inotify_add_watch(), inotify_rm_watch() - Adds/removes watches to monitor filesystem events.

Signalfd

• signalfd() - Creates a file descriptor for accepting signals.

Timerfd

• timerfd_create(), timerfd_settime(), timerfd_gettime() - Creates and manages timers that notify via file descriptors.

Eventfd

• eventfd(), eventfd_read(), eventfd_write() - Provides event notification mechanisms via file descriptors.

Filesystem Interface

Extended Attributes

• setxattr(), getxattr() - Sets/gets extended attributes of files.
• listxattr(), removexattr() - Lists/removes extended attributes.

Filesystem Operations

• mount(), umount(), umount2() - Mounts/unmounts filesystems.
• sync(), syncfs() - Synchronizes filesystem data on disk with memory.
• statvfs(), fstatvfs() - Retrieves filesystem statistics.

File Locking

• flock() - Applies or removes an advisory lock on an open file.
• fcntl() with locking commands (F_GETLK, F_SETLK, F_SETLKW) - Performs record locking operations.

Device and Terminal Control

Terminal I/O (termios)

• tcgetattr(), tcsetattr() - Gets/sets terminal parameters.
• cfgetispeed(), cfsetispeed() - Gets/sets input baud rate.
• cfgetospeed(), cfsetospeed() - Gets/sets output baud rate.
• tcsendbreak() - Transmits a break.
• tcdrain() - Waits until all output is transmitted.
• tcflush() - Discards data written or received.
• tcflow() - Suspends/resumes data transmission or reception.
• tcgetsid() - Gets the session ID.

ioctl Commands

• Various ioctl() commands - Device-specific operations (e.g., controlling hardware devices).

Dynamic Linking and Loading

• dlopen() - Opens a shared library.
• dlsym() - Looks up the address of a symbol.
• dlclose() - Closes a dynamic library.
• dlerror() - Returns error messages from dynamic linking.

Real-Time Extensions

Message Queues

• mq_open(), mq_close() - Opens/closes a message queue.
• mq_unlink() - Removes a message queue.
• mq_send(), mq_receive() - Sends/receives messages.
• mq_notify() - Registers for message queue notification.
• mq_getattr(), mq_setattr() - Gets/sets message queue attributes.

Semaphores

• sem_open(), sem_close() - Opens/closes a named semaphore.
• sem_unlink() - Removes a named semaphore.
• sem_post(), sem_wait() - Increments/decrements a semaphore.
• sem_trywait(), sem_timedwait() - Non-blocking or timed semaphore operations.
• sem_getvalue() - Gets the semaphore value.

Real-Time Signals

• sigqueue() - Sends a signal with accompanying data.

Capability Interfaces

• cap_get_proc(), cap_set_proc() - Gets/sets process capabilities.
• cap_init(), cap_free() - Initializes/frees capability data structures.
• cap_get_flag(), cap_set_flag() - Gets/sets capability flags.

Advanced Memory Management

• mlockall(), munlockall() - Locks/unlocks all pages mapped into the address space.
• madvise(), posix_madvise() - Advises kernel about memory usage patterns.
• mremap() - Remaps a virtual memory address.
• remap_file_pages() - Creates a nonlinear file mapping.

Error Handling

Error Variables and Functions

• errno - Global variable indicating the error code.
• perror() - Prints a descriptive error message.
• strerror(), strerror_r() - Returns a string describing an error code.
• err(), warn() - Error handling functions for reporting.

Atomic Operations

Built-in Functions

• __sync_fetch_and_add(), __sync_fetch_and_sub() - Atomic arithmetic operations.
• __sync_lock_test_and_set(), __sync_lock_release() - Atomic test and set operations.

Atomic Types and Functions

• atomic_flag, atomic_bool, atomic_int, etc. - Atomic data types for thread-safe operations.
• atomic_thread_fence(), atomic_signal_fence() - Memory synchronization operations.

Cryptographic Functions

• crypt() - Performs password encryption.
• getentropy() - Obtains random data.
• getrandom() - Retrieves random bytes from the kernel random number generator.

Locale and Internationalization

• setlocale() - Sets the program’s locale.
• localeconv() - Gets locale-specific formatting information.
• nl_langinfo() - Retrieves information about language-specific settings.

Threading Extensions

Thread Cancellation

• pthread_cancel() - Requests cancellation of a thread.
• pthread_setcancelstate(), pthread_setcanceltype() - Sets cancellation state/type.

Spin Locks

• pthread_spin_init(), pthread_spin_destroy() - Initializes/destroys a spin lock.
• pthread_spin_lock(), pthread_spin_trylock(), pthread_spin_unlock() - Controls a spin lock.

Thread Barriers

• pthread_barrier_init(), pthread_barrier_destroy() - Initializes/destroys a barrier.
• pthread_barrier_wait() - Synchronizes threads at a barrier.

Debugging and Profiling

• gprof() - Profiles program execution.
• mtrace(), muntrace() - Traces dynamic memory allocation.
• backtrace(), backtrace_symbols() - Obtains a backtrace (stack trace).

Miscellaneous Functions

Environment and Configuration

• setreuid(), setregid() - Sets real and effective user/group IDs.
• getresuid(), getresgid() - Gets real, effective, and saved user/group IDs.

Process Groups and Sessions

• setsid(), getsid() - Creates/gets a session ID.
• setpgid(), getpgid(), getpgrp() - Sets/gets process group IDs.

Resource Usage and Limits

• prlimit() - Gets/sets resource limits.

Random Number Generation

• rand(), srand() - Generates pseudo-random numbers.
• random(), srandom(), initstate(), setstate() - Advanced random number functions.

File System Information

• statfs(), fstatfs() - Gets file system statistics.

Linux-Specific System Calls

• clone() - Creates a new process with shared parts.
• unshare() - Disassociates parts of the process execution context.
• setns() - Joins an existing namespace.
• eventfd(), eventfd_read(), eventfd_write() - Provides event notification via file descriptors.
• signalfd() - Creates a file descriptor for accepting signals.
• fanotify_init(), fanotify_mark() - Monitors filesystem events.

Namespace and Control Groups (cgroups)

Namespace Operations

• unshare() - Starts a new namespace.
• setns() - Enters a namespace.

Control Groups Interfaces

• Interactions via filesystem API (e.g., reading/writing to /sys/fs/cgroup/) - Controls resource allocation and usage limits for process groups.