UNIX System Call

aid: unix
name: UNIX System Call
description: >-
  Core UNIX/POSIX system calls providing low-level operating system interfaces for
  process management, file operations, interprocess communication, and system control.
image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
url: >-
  https://raw.githubusercontent.com/api-evangelist/unix/refs/heads/main/apis.yml
type: Index
created: '2024-01-15'
modified: '2026-04-18'
specificationVersion: '0.18'
tags:
  - C-Api
  - Ieee-1003
  - Kernel
  - Open-Group
  - Operating-System
  - Posix
  - System-Calls
  - Unix
common:
  - type: Documentation
    url: https://pubs.opengroup.org/onlinepubs/9799919799/
  - type: Documentation
    url: https://pubs.opengroup.org/onlinepubs/9699919799/
  - type: Documentation
    url: https://man7.org/linux/man-pages/dir_section_2.html
  - type: GettingStarted
    url: https://sourceware.org/glibc/manual/
  - type: Resources
    url: https://en.wikipedia.org/wiki/POSIX
  - type: APIReference
    url: https://unix.org/apis.html
  - type: Documentation
    url: https://standards.ieee.org/ieee/1003.1/7700/
  - type: Features
    data:
      - File system operations and file descriptor management
      - Process creation, execution, and control
      - Interprocess communication via pipes, signals, and sockets
      - Memory mapping and virtual memory management
      - POSIX threads for concurrent programming
      - I/O multiplexing with select and poll
      - Named and unnamed semaphores
      - Message queues for async process communication
      - Terminal and device I/O control
      - Advisory file locking
  - type: UseCases
    data:
      - Operating system development
      - Systems programming and embedded systems
      - Network server and daemon development
      - High-performance I/O applications
      - Concurrent and multi-threaded programming
      - Device driver and hardware interface development
  - type: Integrations
    data:
      - Linux kernel
      - macOS / Darwin
      - FreeBSD
      - GNU C Library (glibc)
      - musl libc
      - POSIX-compliant operating systems
apis:
  - name: File System Operations API
    description: >-
      System calls for file and directory manipulation, including open, read, write,
      and file descriptor management.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/dir_section_2.html
    baseURL: system://unix/fs
    tags:
      - Directories
      - Files
      - Filesystem
      - Io
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/contents.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man2/
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9799919799/functions/open.html
    contact:
      - FN: POSIX Standards Committee
        email: [email protected]
    operations:
      - name: open
        description: Open file and return file descriptor
        parameters:
          - pathname
          - flags
          - mode
        returns: file descriptor (int)
      - name: read
        description: Read bytes from a file descriptor
        parameters:
          - fd
          - buf
          - count
        returns: number of bytes read
      - name: write
        description: Write bytes to a file descriptor
        parameters:
          - fd
          - buf
          - count
        returns: number of bytes written
      - name: close
        description: Close a file descriptor
        parameters:
          - fd
        returns: 0 on success, -1 on error
      - name: lseek
        description: Reposition file offset
        parameters:
          - fd
          - offset
          - whence
        returns: resulting offset
      - name: stat
        description: Get file status
        parameters:
          - pathname
          - statbuf
        returns: 0 on success, -1 on error
      - name: fstat
        description: Get file status by file descriptor
        parameters:
          - fd
          - statbuf
        returns: 0 on success, -1 on error
      - name: lstat
        description: Get file status without following symbolic links
        parameters:
          - pathname
          - statbuf
        returns: 0 on success, -1 on error
      - name: chmod
        description: Change file permissions
        parameters:
          - pathname
          - mode
        returns: 0 on success, -1 on error
      - name: fchmod
        description: Change file permissions by file descriptor
        parameters:
          - fd
          - mode
        returns: 0 on success, -1 on error
      - name: chown
        description: Change file owner and group
        parameters:
          - pathname
          - owner
          - group
        returns: 0 on success, -1 on error
      - name: mkdir
        description: Create a directory
        parameters:
          - pathname
          - mode
        returns: 0 on success, -1 on error
      - name: rmdir
        description: Remove a directory
        parameters:
          - pathname
        returns: 0 on success, -1 on error
      - name: link
        description: Create a hard link to a file
        parameters:
          - oldpath
          - newpath
        returns: 0 on success, -1 on error
      - name: unlink
        description: Delete a name and possibly the file it refers to
        parameters:
          - pathname
        returns: 0 on success, -1 on error
      - name: symlink
        description: Create a symbolic link
        parameters:
          - target
          - linkpath
        returns: 0 on success, -1 on error
      - name: readlink
        description: Read value of a symbolic link
        parameters:
          - pathname
          - buf
          - bufsiz
        returns: number of bytes placed in buf
      - name: rename
        description: Change the name or location of a file
        parameters:
          - oldpath
          - newpath
        returns: 0 on success, -1 on error
      - name: dup
        description: Duplicate a file descriptor
        parameters:
          - oldfd
        returns: new file descriptor
      - name: dup2
        description: Duplicate a file descriptor to a specified descriptor number
        parameters:
          - oldfd
          - newfd
        returns: new file descriptor
      - name: fcntl
        description: Manipulate file descriptor properties and flags
        parameters:
          - fd
          - cmd
          - arg
        returns: depends on cmd, -1 on error
      - name: access
        description: Check user permissions for a file
        parameters:
          - pathname
          - mode
        returns: 0 on success, -1 on error
      - name: umask
        description: Set file mode creation mask
        parameters:
          - mask
        returns: previous value of the mask
      - name: opendir
        description: Open a directory stream
        parameters:
          - name
        returns: pointer to directory stream
      - name: readdir
        description: Read a directory entry
        parameters:
          - dirp
        returns: pointer to dirent structure
      - name: closedir
        description: Close a directory stream
        parameters:
          - dirp
        returns: 0 on success, -1 on error
      - name: chdir
        description: Change working directory
        parameters:
          - path
        returns: 0 on success, -1 on error
      - name: getcwd
        description: Get current working directory
        parameters:
          - buf
          - size
        returns: pointer to buf
      - name: truncate
        description: Truncate a file to a specified length
        parameters:
          - path
          - length
        returns: 0 on success, -1 on error
      - name: ftruncate
        description: Truncate an open file to a specified length
        parameters:
          - fd
          - length
        returns: 0 on success, -1 on error
      - name: fsync
        description: Synchronize file state with storage device
        parameters:
          - fd
        returns: 0 on success, -1 on error
  - name: Process Management API
    description: >-
      System calls for process creation, execution, termination, and control.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man2/fork.2.html
    baseURL: system://unix/process
    tags:
      - Execution
      - Processes
      - Scheduling
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/fork.html
      - type: GettingStarted
        url: https://sourceware.org/glibc/manual/
      - type: APIReference
        url: https://man7.org/linux/man-pages/man2/fork.2.html
    operations:
      - name: fork
        description: Create a new process by duplicating the calling process
        parameters: []
        returns: PID of child (in parent), 0 (in child), -1 on error
      - name: exec
        description: Execute a program (family of functions - execl, execv, execve, etc.)
        parameters:
          - pathname
          - argv
          - envp
        returns: does not return on success, -1 on error
      - name: wait
        description: Wait for process to change state
        parameters:
          - status
        returns: PID of terminated child
      - name: waitpid
        description: Wait for specific process to change state
        parameters:
          - pid
          - status
          - options
        returns: PID of child
      - name: exit
        description: Terminate the calling process
        parameters:
          - status
        returns: does not return
      - name: _exit
        description: Terminate the calling process immediately without cleanup
        parameters:
          - status
        returns: does not return
      - name: getpid
        description: Get process ID
        parameters: []
        returns: process ID
      - name: getppid
        description: Get parent process ID
        parameters: []
        returns: parent process ID
      - name: kill
        description: Send signal to a process
        parameters:
          - pid
          - sig
        returns: 0 on success, -1 on error
      - name: nice
        description: Change process priority
        parameters:
          - inc
        returns: new nice value
      - name: setpgid
        description: Set process group ID
        parameters:
          - pid
          - pgid
        returns: 0 on success, -1 on error
      - name: getpgid
        description: Get process group ID
        parameters:
          - pid
        returns: process group ID
      - name: setsid
        description: Create a new session and set process group ID
        parameters: []
        returns: session ID of new session
      - name: getrlimit
        description: Get resource limits for the process
        parameters:
          - resource
          - rlim
        returns: 0 on success, -1 on error
      - name: setrlimit
        description: Set resource limits for the process
        parameters:
          - resource
          - rlim
        returns: 0 on success, -1 on error
      - name: alarm
        description: Set an alarm clock for delivery of a signal
        parameters:
          - seconds
        returns: remaining seconds of previous alarm
      - name: pause
        description: Wait for a signal
        parameters: []
        returns: -1 with errno set to EINTR
      - name: posix_spawn
        description: Spawn a new process without fork (POSIX.1-2001)
        parameters:
          - pid
          - path
          - file_actions
          - attrp
          - argv
          - envp
        returns: 0 on success, error number on failure
  - name: Interprocess Communication API
    description: >-
      System calls for communication between processes including pipes, signals, and
      shared memory.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man7/pipe.7.html
    baseURL: system://unix/ipc
    tags:
      - Ipc
      - Pipes
      - Shared-Memory
      - Signals
      - Sockets
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/V2_chap02.html
      - type: CodeExamples
        url: https://beej.us/guide/bgipc/
      - type: GettingStarted
        url: https://beej.us/guide/bgnet/html/
      - type: APIReference
        url: https://man7.org/linux/man-pages/man7/pipe.7.html
    operations:
      - name: pipe
        description: Create a pipe for interprocess communication
        parameters:
          - pipefd[2]
        returns: 0 on success, -1 on error
      - name: mkfifo
        description: Create a named pipe (FIFO special file)
        parameters:
          - pathname
          - mode
        returns: 0 on success, -1 on error
      - name: signal
        description: Install signal handler
        parameters:
          - signum
          - handler
        returns: previous signal handler
      - name: sigaction
        description: Examine and change signal action
        parameters:
          - signum
          - act
          - oldact
        returns: 0 on success, -1 on error
      - name: sigprocmask
        description: Examine and change blocked signals
        parameters:
          - how
          - set
          - oldset
        returns: 0 on success, -1 on error
      - name: sigpending
        description: Examine pending signals
        parameters:
          - set
        returns: 0 on success, -1 on error
      - name: sigsuspend
        description: Wait for a signal replacing the signal mask
        parameters:
          - mask
        returns: -1 with errno set to EINTR
      - name: socket
        description: Create an endpoint for communication
        parameters:
          - domain
          - type
          - protocol
        returns: file descriptor
      - name: bind
        description: Bind a name to a socket
        parameters:
          - sockfd
          - addr
          - addrlen
        returns: 0 on success, -1 on error
      - name: listen
        description: Listen for connections on a socket
        parameters:
          - sockfd
          - backlog
        returns: 0 on success, -1 on error
      - name: accept
        description: Accept a connection on a socket
        parameters:
          - sockfd
          - addr
          - addrlen
        returns: file descriptor
      - name: connect
        description: Initiate a connection on a socket
        parameters:
          - sockfd
          - addr
          - addrlen
        returns: 0 on success, -1 on error
      - name: send
        description: Send a message on a socket
        parameters:
          - sockfd
          - buf
          - len
          - flags
        returns: number of bytes sent
      - name: recv
        description: Receive a message from a socket
        parameters:
          - sockfd
          - buf
          - len
          - flags
        returns: number of bytes received
      - name: sendto
        description: Send a message on a socket to a specified address
        parameters:
          - sockfd
          - buf
          - len
          - flags
          - dest_addr
          - addrlen
        returns: number of bytes sent
      - name: recvfrom
        description: Receive a message from a socket with sender address
        parameters:
          - sockfd
          - buf
          - len
          - flags
          - src_addr
          - addrlen
        returns: number of bytes received
      - name: shutdown
        description: Shut down part of a full-duplex connection
        parameters:
          - sockfd
          - how
        returns: 0 on success, -1 on error
      - name: setsockopt
        description: Set options on a socket
        parameters:
          - sockfd
          - level
          - optname
          - optval
          - optlen
        returns: 0 on success, -1 on error
      - name: getsockopt
        description: Get options on a socket
        parameters:
          - sockfd
          - level
          - optname
          - optval
          - optlen
        returns: 0 on success, -1 on error
      - name: socketpair
        description: Create a pair of connected sockets
        parameters:
          - domain
          - type
          - protocol
          - sv[2]
        returns: 0 on success, -1 on error
      - name: shmget
        description: Allocate shared memory segment
        parameters:
          - key
          - size
          - shmflg
        returns: shared memory identifier
      - name: shmat
        description: Attach shared memory segment
        parameters:
          - shmid
          - shmaddr
          - shmflg
        returns: pointer to shared memory
      - name: shmdt
        description: Detach shared memory segment
        parameters:
          - shmaddr
        returns: 0 on success, -1 on error
      - name: shmctl
        description: Shared memory control operations
        parameters:
          - shmid
          - cmd
          - buf
        returns: depends on cmd, -1 on error
      - name: msgget
        description: Get a System V message queue identifier
        parameters:
          - key
          - msgflg
        returns: message queue identifier
      - name: msgsnd
        description: Send a message to a System V message queue
        parameters:
          - msqid
          - msgp
          - msgsz
          - msgflg
        returns: 0 on success, -1 on error
      - name: msgrcv
        description: Receive a message from a System V message queue
        parameters:
          - msqid
          - msgp
          - msgsz
          - msgtyp
          - msgflg
        returns: number of bytes copied into msgp
      - name: msgctl
        description: System V message queue control operations
        parameters:
          - msqid
          - cmd
          - buf
        returns: depends on cmd, -1 on error
  - name: Memory Management API
    description: >-
      System calls for memory allocation, mapping, and protection.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man2/mmap.2.html
    baseURL: system://unix/memory
    tags:
      - Allocation
      - Memory
      - Mmap
      - Virtual-Memory
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/mmap.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man2/mmap.2.html
    operations:
      - name: brk
        description: Change data segment size
        parameters:
          - addr
        returns: 0 on success, -1 on error
      - name: sbrk
        description: Change data segment size
        parameters:
          - increment
        returns: previous program break
      - name: mmap
        description: Map files or devices into memory
        parameters:
          - addr
          - length
          - prot
          - flags
          - fd
          - offset
        returns: pointer to mapped area
      - name: munmap
        description: Unmap files or devices from memory
        parameters:
          - addr
          - length
        returns: 0 on success, -1 on error
      - name: mprotect
        description: Set protection on a region of memory
        parameters:
          - addr
          - len
          - prot
        returns: 0 on success, -1 on error
      - name: mlock
        description: Lock memory into RAM
        parameters:
          - addr
          - len
        returns: 0 on success, -1 on error
      - name: munlock
        description: Unlock memory from RAM
        parameters:
          - addr
          - len
        returns: 0 on success, -1 on error
      - name: msync
        description: Synchronize a memory-mapped file with its underlying storage
        parameters:
          - addr
          - length
          - flags
        returns: 0 on success, -1 on error
      - name: madvise
        description: Give advice about use of memory to the kernel
        parameters:
          - addr
          - length
          - advice
        returns: 0 on success, -1 on error
      - name: posix_memalign
        description: Allocate aligned memory
        parameters:
          - memptr
          - alignment
          - size
        returns: 0 on success, error number on failure
      - name: shm_open
        description: Create or open a POSIX shared memory object
        parameters:
          - name
          - oflag
          - mode
        returns: file descriptor
      - name: shm_unlink
        description: Remove a POSIX shared memory object
        parameters:
          - name
        returns: 0 on success, -1 on error
  - name: System Information API
    description: >-
      System calls for retrieving system information and configuration.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man2/uname.2.html
    baseURL: system://unix/sysinfo
    tags:
      - Configuration
      - Groups
      - Information
      - System
      - Users
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/uname.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man2/uname.2.html
    operations:
      - name: uname
        description: Get system information
        parameters:
          - buf
        returns: 0 on success, -1 on error
      - name: getuid
        description: Get user identity
        parameters: []
        returns: user ID
      - name: getgid
        description: Get group identity
        parameters: []
        returns: group ID
      - name: geteuid
        description: Get effective user ID
        parameters: []
        returns: effective user ID
      - name: getegid
        description: Get effective group ID
        parameters: []
        returns: effective group ID
      - name: setuid
        description: Set user identity
        parameters:
          - uid
        returns: 0 on success, -1 on error
      - name: setgid
        description: Set group identity
        parameters:
          - gid
        returns: 0 on success, -1 on error
      - name: seteuid
        description: Set effective user ID
        parameters:
          - euid
        returns: 0 on success, -1 on error
      - name: setegid
        description: Set effective group ID
        parameters:
          - egid
        returns: 0 on success, -1 on error
      - name: getgroups
        description: Get supplementary group IDs
        parameters:
          - size
          - list
        returns: number of supplementary group IDs
      - name: getlogin
        description: Get login name
        parameters: []
        returns: pointer to login name string
      - name: time
        description: Get time in seconds since Epoch
        parameters:
          - tloc
        returns: time value
      - name: gettimeofday
        description: Get time with microsecond precision
        parameters:
          - tv
          - tz
        returns: 0 on success, -1 on error
      - name: clock_gettime
        description: Get time from a specified clock with nanosecond precision
        parameters:
          - clockid
          - tp
        returns: 0 on success, -1 on error
      - name: clock_settime
        description: Set time for a specified clock
        parameters:
          - clockid
          - tp
        returns: 0 on success, -1 on error
      - name: sysconf
        description: Get configurable system variables at runtime
        parameters:
          - name
        returns: value of system variable, -1 on error
      - name: pathconf
        description: Get configurable pathname variables
        parameters:
          - path
          - name
        returns: value of variable, -1 on error
      - name: getenv
        description: Get value of an environment variable
        parameters:
          - name
        returns: pointer to value string, NULL if not found
      - name: setenv
        description: Set or change an environment variable
        parameters:
          - name
          - value
          - overwrite
        returns: 0 on success, -1 on error
      - name: gethostname
        description: Get the hostname of the system
        parameters:
          - name
          - len
        returns: 0 on success, -1 on error
  - name: POSIX Threads API
    description: >-
      POSIX threads (pthreads) interface for creating and managing threads, mutexes,
      condition variables, and thread-specific data.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man7/pthreads.7.html
    baseURL: system://unix/pthreads
    tags:
      - Concurrency
      - Mutexes
      - Pthreads
      - Synchronization
      - Threads
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/pthread_create.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man7/pthreads.7.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man0/pthread.h.0p.html
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9799919799/functions/pthread_create.html
    operations:
      - name: pthread_create
        description: Create a new thread
        parameters:
          - thread
          - attr
          - start_routine
          - arg
        returns: 0 on success, error number on failure
      - name: pthread_exit
        description: Terminate the calling thread
        parameters:
          - retval
        returns: does not return
      - name: pthread_join
        description: Wait for a thread to terminate
        parameters:
          - thread
          - retval
        returns: 0 on success, error number on failure
      - name: pthread_detach
        description: Detach a thread so its resources are freed on termination
        parameters:
          - thread
        returns: 0 on success, error number on failure
      - name: pthread_self
        description: Obtain ID of the calling thread
        parameters: []
        returns: thread ID
      - name: pthread_equal
        description: Compare two thread IDs
        parameters:
          - t1
          - t2
        returns: nonzero if equal, 0 if not equal
      - name: pthread_cancel
        description: Send a cancellation request to a thread
        parameters:
          - thread
        returns: 0 on success, error number on failure
      - name: pthread_mutex_init
        description: Initialize a mutex
        parameters:
          - mutex
          - attr
        returns: 0 on success, error number on failure
      - name: pthread_mutex_destroy
        description: Destroy a mutex
        parameters:
          - mutex
        returns: 0 on success, error number on failure
      - name: pthread_mutex_lock
        description: Lock a mutex
        parameters:
          - mutex
        returns: 0 on success, error number on failure
      - name: pthread_mutex_trylock
        description: Try to lock a mutex without blocking
        parameters:
          - mutex
        returns: 0 on success, error number on failure
      - name: pthread_mutex_unlock
        description: Unlock a mutex
        parameters:
          - mutex
        returns: 0 on success, error number on failure
      - name: pthread_cond_init
        description: Initialize a condition variable
        parameters:
          - cond
          - attr
        returns: 0 on success, error number on failure
      - name: pthread_cond_destroy
        description: Destroy a condition variable
        parameters:
          - cond
        returns: 0 on success, error number on failure
      - name: pthread_cond_wait
        description: Wait on a condition variable
        parameters:
          - cond
          - mutex
        returns: 0 on success, error number on failure
      - name: pthread_cond_signal
        description: Signal a condition variable waking one waiting thread
        parameters:
          - cond
        returns: 0 on success, error number on failure
      - name: pthread_cond_broadcast
        description: Broadcast a condition variable waking all waiting threads
        parameters:
          - cond
        returns: 0 on success, error number on failure
      - name: pthread_rwlock_init
        description: Initialize a read-write lock
        parameters:
          - rwlock
          - attr
        returns: 0 on success, error number on failure
      - name: pthread_rwlock_rdlock
        description: Lock a read-write lock for reading
        parameters:
          - rwlock
        returns: 0 on success, error number on failure
      - name: pthread_rwlock_wrlock
        description: Lock a read-write lock for writing
        parameters:
          - rwlock
        returns: 0 on success, error number on failure
      - name: pthread_rwlock_unlock
        description: Unlock a read-write lock
        parameters:
          - rwlock
        returns: 0 on success, error number on failure
      - name: pthread_key_create
        description: Create a thread-specific data key
        parameters:
          - key
          - destructor
        returns: 0 on success, error number on failure
      - name: pthread_setspecific
        description: Set thread-specific data value
        parameters:
          - key
          - value
        returns: 0 on success, error number on failure
      - name: pthread_getspecific
        description: Get thread-specific data value
        parameters:
          - key
        returns: pointer to thread-specific data, NULL if no value set
      - name: pthread_once
        description: Ensure initialization routine is called exactly once
        parameters:
          - once_control
          - init_routine
        returns: 0 on success, error number on failure
      - name: pthread_attr_init
        description: Initialize thread attributes object
        parameters:
          - attr
        returns: 0 on success, error number on failure
      - name: pthread_attr_destroy
        description: Destroy thread attributes object
        parameters:
          - attr
        returns: 0 on success, error number on failure
  - name: I/O Multiplexing API
    description: >-
      System calls for monitoring multiple file descriptors for readiness, enabling
      event-driven and non-blocking I/O patterns.
    image: https://kinlane-productions.s3.amazonaws.com/apis-json/apis-json-logo.jpg
    humanURL: https://man7.org/linux/man-pages/man2/select.2.html
    baseURL: system://unix/io-multiplex
    tags:
      - Event-Driven
      - Io
      - Multiplexing
      - Non-Blocking
      - Poll
      - Select
    properties:
      - type: Documentation
        url: https://pubs.opengroup.org/onlinepubs/9699919799/functions/select.html
      - type: APIReference
        url: https://man7.org/linux/man-pages/man2/select.2.html
      - type: Tutorials
        url: https://man7.org/linux/man-pages/man2/select_tut.2.html
    operations:
      - name: select
        description: Monitor multiple file descriptors for readiness using fd_set bitmasks
        parameters:
          - nfds
          - readfds
          - writefds
          - exceptfds
          - timeout
        returns: number of ready descriptors, 0 on timeout, -1 on error
      - name: pselect
        description: Synchronous I/O multiplexing with signal mask and timespec timeout
        parameters:
          - nfds
          - readfds
          - writefds
          - exceptfds
          - timeout
          - sigmask
        returns: number of ready descriptors, 0 on timeout, -1 on error
      - name: poll
        description: Monitor multiple file descriptors using pollfd array
        parameters:
          - fds
          - nfds
          - timeout
        returns: number of ready descriptors, 0 on timeout, -1 on error
      - name: ppoll
        description: Poll file descriptors with signal mask and timespec timeout
        parameters:
          - fds
          - nfds
          - tmo_p
          - sigmask
        returns: number of ready descriptors, 0 on timeout, -1 on error
  - name: POSIX Semapho

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