unistd.h 是 C 和 C++ 程序设计语言中提供对 POSIX 操作系统 API 的访问功能的头文件的名称。该头文件由 POSIX.1 标准（单一UNIX规范的基础）提出，故所有遵循该标准的操作系统和编译器均应提供该头文件（如 Unix 的所有官方版本，包括 Mac OS X、Linux 等）。

对于类 Unix 系统，unistd.h 中所定义的接口通常都是大量针对系统调用的封装（英语：wrapper functions），如 fork、pipe 以及各种 I/O 原语（read、write、close 等等）。

类似于 Cygwin 和 MinGW 的 Unix 兼容层也提供相应版本的 unistd.h。

unistd.h在linux内核中的源码：

/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
/*
 * IA-64 Linux syscall numbers and inline-functions.
 *
 * Copyright (C) 1998-2005 Hewlett-Packard Co
 *	David Mosberger-Tang <davidm@hpl.hp.com>
 */
#ifndef _UAPI_ASM_IA64_UNISTD_H
#define _UAPI_ASM_IA64_UNISTD_H


#include <asm/break.h>

#define __BREAK_SYSCALL			__IA64_BREAK_SYSCALL

#define __NR_ni_syscall			1024
#define __NR_exit			1025
#define __NR_read			1026
#define __NR_write			1027
#define __NR_open			1028
#define __NR_close			1029
#define __NR_creat			1030
#define __NR_link			1031
#define __NR_unlink			1032
#define __NR_execve			1033
#define __NR_chdir			1034
#define __NR_fchdir			1035
#define __NR_utimes			1036
#define __NR_mknod			1037
#define __NR_chmod			1038
#define __NR_chown			1039
#define __NR_lseek			1040
#define __NR_getpid			1041
#define __NR_getppid			1042
#define __NR_mount			1043
#define __NR_umount			1044
#define __NR_setuid			1045
#define __NR_getuid			1046
#define __NR_geteuid			1047
#define __NR_ptrace			1048
#define __NR_access			1049
#define __NR_sync			1050
#define __NR_fsync			1051
#define __NR_fdatasync			1052
#define __NR_kill			1053
#define __NR_rename			1054
#define __NR_mkdir			1055
#define __NR_rmdir			1056
#define __NR_dup			1057
#define __NR_pipe			1058
#define __NR_times			1059
#define __NR_brk			1060
#define __NR_setgid			1061
#define __NR_getgid			1062
#define __NR_getegid			1063
#define __NR_acct			1064
#define __NR_ioctl			1065
#define __NR_fcntl			1066
#define __NR_umask			1067
#define __NR_chroot			1068
#define __NR_ustat			1069
#define __NR_dup2			1070
#define __NR_setreuid			1071
#define __NR_setregid			1072
#define __NR_getresuid			1073
#define __NR_setresuid			1074
#define __NR_getresgid			1075
#define __NR_setresgid			1076
#define __NR_getgroups			1077
#define __NR_setgroups			1078
#define __NR_getpgid			1079
#define __NR_setpgid			1080
#define __NR_setsid			1081
#define __NR_getsid			1082
#define __NR_sethostname		1083
#define __NR_setrlimit			1084
#define __NR_getrlimit			1085
#define __NR_getrusage			1086
#define __NR_gettimeofday		1087
#define __NR_settimeofday		1088
#define __NR_select			1089
#define __NR_poll			1090
#define __NR_symlink			1091
#define __NR_readlink			1092
#define __NR_uselib			1093
#define __NR_swapon			1094
#define __NR_swapoff			1095
#define __NR_reboot			1096
#define __NR_truncate			1097
#define __NR_ftruncate			1098
#define __NR_fchmod			1099
#define __NR_fchown			1100
#define __NR_getpriority		1101
#define __NR_setpriority		1102
#define __NR_statfs			1103
#define __NR_fstatfs			1104
#define __NR_gettid			1105
#define __NR_semget			1106
#define __NR_semop			1107
#define __NR_semctl			1108
#define __NR_msgget			1109
#define __NR_msgsnd			1110
#define __NR_msgrcv			1111
#define __NR_msgctl			1112
#define __NR_shmget			1113
#define __NR_shmat			1114
#define __NR_shmdt			1115
#define __NR_shmctl			1116
/* also known as klogctl() in GNU libc: */
#define __NR_syslog			1117
#define __NR_setitimer			1118
#define __NR_getitimer			1119
/* 1120 was __NR_old_stat */
/* 1121 was __NR_old_lstat */
/* 1122 was __NR_old_fstat */
#define __NR_vhangup			1123
#define __NR_lchown			1124
#define __NR_remap_file_pages		1125
#define __NR_wait4			1126
#define __NR_sysinfo			1127
#define __NR_clone			1128
#define __NR_setdomainname		1129
#define __NR_uname			1130
#define __NR_adjtimex			1131
/* 1132 was __NR_create_module */
#define __NR_init_module		1133
#define __NR_delete_module		1134
/* 1135 was __NR_get_kernel_syms */
/* 1136 was __NR_query_module */
#define __NR_quotactl			1137
#define __NR_bdflush			1138
#define __NR_sysfs			1139
#define __NR_personality		1140
#define __NR_afs_syscall		1141
#define __NR_setfsuid			1142
#define __NR_setfsgid			1143
#define __NR_getdents			1144
#define __NR_flock			1145
#define __NR_readv			1146
#define __NR_writev			1147
#define __NR_pread64			1148
#define __NR_pwrite64			1149
#define __NR__sysctl			1150
#define __NR_mmap			1151
#define __NR_munmap			1152
#define __NR_mlock			1153
#define __NR_mlockall			1154
#define __NR_mprotect			1155
#define __NR_mremap			1156
#define __NR_msync			1157
#define __NR_munlock			1158
#define __NR_munlockall			1159
#define __NR_sched_getparam		1160
#define __NR_sched_setparam		1161
#define __NR_sched_getscheduler		1162
#define __NR_sched_setscheduler		1163
#define __NR_sched_yield		1164
#define __NR_sched_get_priority_max	1165
#define __NR_sched_get_priority_min	1166
#define __NR_sched_rr_get_interval	1167
#define __NR_nanosleep			1168
#define __NR_nfsservctl			1169
#define __NR_prctl			1170
/* 1171 is reserved for backwards compatibility with old __NR_getpagesize */
#define __NR_mmap2			1172
#define __NR_pciconfig_read		1173
#define __NR_pciconfig_write		1174
#define __NR_perfmonctl			1175
#define __NR_sigaltstack		1176
#define __NR_rt_sigaction		1177
#define __NR_rt_sigpending		1178
#define __NR_rt_sigprocmask		1179
#define __NR_rt_sigqueueinfo		1180
#define __NR_rt_sigreturn		1181
#define __NR_rt_sigsuspend		1182
#define __NR_rt_sigtimedwait		1183
#define __NR_getcwd			1184
#define __NR_capget			1185
#define __NR_capset			1186
#define __NR_sendfile			1187
#define __NR_getpmsg			1188
#define __NR_putpmsg			1189
#define __NR_socket			1190
#define __NR_bind			1191
#define __NR_connect			1192
#define __NR_listen			1193
#define __NR_accept			1194
#define __NR_getsockname		1195
#define __NR_getpeername		1196
#define __NR_socketpair			1197
#define __NR_send			1198
#define __NR_sendto			1199
#define __NR_recv			1200
#define __NR_recvfrom			1201
#define __NR_shutdown			1202
#define __NR_setsockopt			1203
#define __NR_getsockopt			1204
#define __NR_sendmsg			1205
#define __NR_recvmsg			1206
#define __NR_pivot_root			1207
#define __NR_mincore			1208
#define __NR_madvise			1209
#define __NR_stat			1210
#define __NR_lstat			1211
#define __NR_fstat			1212
#define __NR_clone2			1213
#define __NR_getdents64			1214
#define __NR_getunwind			1215
#define __NR_readahead			1216
#define __NR_setxattr			1217
#define __NR_lsetxattr			1218
#define __NR_fsetxattr			1219
#define __NR_getxattr			1220
#define __NR_lgetxattr			1221
#define __NR_fgetxattr			1222
#define __NR_listxattr			1223
#define __NR_llistxattr			1224
#define __NR_flistxattr			1225
#define __NR_removexattr		1226
#define __NR_lremovexattr		1227
#define __NR_fremovexattr		1228
#define __NR_tkill			1229
#define __NR_futex			1230
#define __NR_sched_setaffinity		1231
#define __NR_sched_getaffinity		1232
#define __NR_set_tid_address		1233
#define __NR_fadvise64			1234
#define __NR_tgkill			1235
#define __NR_exit_group			1236
#define __NR_lookup_dcookie		1237
#define __NR_io_setup			1238
#define __NR_io_destroy			1239
#define __NR_io_getevents		1240
#define __NR_io_submit			1241
#define __NR_io_cancel			1242
#define __NR_epoll_create		1243
#define __NR_epoll_ctl			1244
#define __NR_epoll_wait			1245
#define __NR_restart_syscall		1246
#define __NR_semtimedop			1247
#define __NR_timer_create		1248
#define __NR_timer_settime		1249
#define __NR_timer_gettime		1250
#define __NR_timer_getoverrun		1251
#define __NR_timer_delete		1252
#define __NR_clock_settime		1253
#define __NR_clock_gettime		1254
#define __NR_clock_getres		1255
#define __NR_clock_nanosleep		1256
#define __NR_fstatfs64			1257
#define __NR_statfs64			1258
#define __NR_mbind			1259
#define __NR_get_mempolicy		1260
#define __NR_set_mempolicy		1261
#define __NR_mq_open			1262
#define __NR_mq_unlink			1263
#define __NR_mq_timedsend		1264
#define __NR_mq_timedreceive		1265
#define __NR_mq_notify			1266
#define __NR_mq_getsetattr		1267
#define __NR_kexec_load			1268
#define __NR_vserver			1269
#define __NR_waitid			1270
#define __NR_add_key			1271
#define __NR_request_key		1272
#define __NR_keyctl			1273
#define __NR_ioprio_set			1274
#define __NR_ioprio_get			1275
#define __NR_move_pages			1276
#define __NR_inotify_init		1277
#define __NR_inotify_add_watch		1278
#define __NR_inotify_rm_watch		1279
#define __NR_migrate_pages		1280
#define __NR_openat			1281
#define __NR_mkdirat			1282
#define __NR_mknodat			1283
#define __NR_fchownat			1284
#define __NR_futimesat			1285
#define __NR_newfstatat			1286
#define __NR_unlinkat			1287
#define __NR_renameat			1288
#define __NR_linkat			1289
#define __NR_symlinkat			1290
#define __NR_readlinkat			1291
#define __NR_fchmodat			1292
#define __NR_faccessat			1293
#define __NR_pselect6			1294
#define __NR_ppoll			1295
#define __NR_unshare			1296
#define __NR_splice			1297
#define __NR_set_robust_list		1298
#define __NR_get_robust_list		1299
#define __NR_sync_file_range		1300
#define __NR_tee			1301
#define __NR_vmsplice			1302
#define __NR_fallocate			1303
#define __NR_getcpu			1304
#define __NR_epoll_pwait		1305
#define __NR_utimensat			1306
#define __NR_signalfd			1307
#define __NR_timerfd			1308
#define __NR_eventfd			1309
#define __NR_timerfd_create		1310
#define __NR_timerfd_settime		1311
#define __NR_timerfd_gettime		1312
#define __NR_signalfd4			1313
#define __NR_eventfd2			1314
#define __NR_epoll_create1		1315
#define __NR_dup3			1316
#define __NR_pipe2			1317
#define __NR_inotify_init1		1318
#define __NR_preadv			1319
#define __NR_pwritev			1320
#define __NR_rt_tgsigqueueinfo		1321
#define __NR_recvmmsg			1322
#define __NR_fanotify_init		1323
#define __NR_fanotify_mark		1324
#define __NR_prlimit64			1325
#define __NR_name_to_handle_at		1326
#define __NR_open_by_handle_at  	1327
#define __NR_clock_adjtime		1328
#define __NR_syncfs			1329
#define __NR_setns			1330
#define __NR_sendmmsg			1331
#define __NR_process_vm_readv		1332
#define __NR_process_vm_writev		1333
#define __NR_accept4			1334
#define __NR_finit_module		1335
#define __NR_sched_setattr		1336
#define __NR_sched_getattr		1337
#define __NR_renameat2			1338
#define __NR_getrandom			1339
#define __NR_memfd_create		1340
#define __NR_bpf			1341
#define __NR_execveat			1342
#define __NR_userfaultfd		1343
#define __NR_membarrier			1344
#define __NR_kcmp			1345
#define __NR_mlock2			1346
#define __NR_copy_file_range		1347
#define __NR_preadv2			1348
#define __NR_pwritev2			1349

#endif /* _UAPI_ASM_IA64_UNISTD_H */

unistd.h在glibc中的源码：

/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <http://www.gnu.org/licenses/>.  */

/*
 *	POSIX Standard: 2.10 Symbolic Constants		<unistd.h>
 */

#ifndef	_UNISTD_H
#define	_UNISTD_H	1

#include <features.h>

__BEGIN_DECLS

/* These may be used to determine what facilities are present at compile time.
   Their values can be obtained at run time from `sysconf'.  */

#ifdef __USE_XOPEN2K8
/* POSIX Standard approved as ISO/IEC 9945-1 as of September 2008.  */
# define _POSIX_VERSION	200809L
#elif defined __USE_XOPEN2K
/* POSIX Standard approved as ISO/IEC 9945-1 as of December 2001.  */
# define _POSIX_VERSION	200112L
#elif defined __USE_POSIX199506
/* POSIX Standard approved as ISO/IEC 9945-1 as of June 1995.  */
# define _POSIX_VERSION	199506L
#elif defined __USE_POSIX199309
/* POSIX Standard approved as ISO/IEC 9945-1 as of September 1993.  */
# define _POSIX_VERSION	199309L
#else
/* POSIX Standard approved as ISO/IEC 9945-1 as of September 1990.  */
# define _POSIX_VERSION	199009L
#endif

/* These are not #ifdef __USE_POSIX2 because they are
   in the theoretically application-owned namespace.  */

#ifdef __USE_XOPEN2K8
# define __POSIX2_THIS_VERSION	200809L
/* The utilities on GNU systems also correspond to this version.  */
#elif defined __USE_XOPEN2K
/* The utilities on GNU systems also correspond to this version.  */
# define __POSIX2_THIS_VERSION	200112L
#elif defined __USE_POSIX199506
/* The utilities on GNU systems also correspond to this version.  */
# define __POSIX2_THIS_VERSION	199506L
#else
/* The utilities on GNU systems also correspond to this version.  */
# define __POSIX2_THIS_VERSION	199209L
#endif

/* The utilities on GNU systems also correspond to this version.  */
#define _POSIX2_VERSION	__POSIX2_THIS_VERSION

/* This symbol was required until the 2001 edition of POSIX.  */
#define	_POSIX2_C_VERSION	__POSIX2_THIS_VERSION

/* If defined, the implementation supports the
   C Language Bindings Option.  */
#define	_POSIX2_C_BIND	__POSIX2_THIS_VERSION

/* If defined, the implementation supports the
   C Language Development Utilities Option.  */
#define	_POSIX2_C_DEV	__POSIX2_THIS_VERSION

/* If defined, the implementation supports the
   Software Development Utilities Option.  */
#define	_POSIX2_SW_DEV	__POSIX2_THIS_VERSION

/* If defined, the implementation supports the
   creation of locales with the localedef utility.  */
#define _POSIX2_LOCALEDEF       __POSIX2_THIS_VERSION

/* X/Open version number to which the library conforms.  It is selectable.  */
#ifdef __USE_XOPEN2K8
# define _XOPEN_VERSION	700
#elif defined __USE_XOPEN2K
# define _XOPEN_VERSION	600
#elif defined __USE_UNIX98
# define _XOPEN_VERSION	500
#else
# define _XOPEN_VERSION	4
#endif

/* Commands and utilities from XPG4 are available.  */
#define _XOPEN_XCU_VERSION	4

/* We are compatible with the old published standards as well.  */
#define _XOPEN_XPG2	1
#define _XOPEN_XPG3	1
#define _XOPEN_XPG4	1

/* The X/Open Unix extensions are available.  */
#define _XOPEN_UNIX	1

/* The enhanced internationalization capabilities according to XPG4.2
   are present.  */
#define	_XOPEN_ENH_I18N	1

/* The legacy interfaces are also available.  */
#define _XOPEN_LEGACY	1


/* Get values of POSIX options:

   If these symbols are defined, the corresponding features are
   always available.  If not, they may be available sometimes.
   The current values can be obtained with `sysconf'.

   _POSIX_JOB_CONTROL		Job control is supported.
   _POSIX_SAVED_IDS		Processes have a saved set-user-ID
				and a saved set-group-ID.
   _POSIX_REALTIME_SIGNALS	Real-time, queued signals are supported.
   _POSIX_PRIORITY_SCHEDULING	Priority scheduling is supported.
   _POSIX_TIMERS		POSIX.4 clocks and timers are supported.
   _POSIX_ASYNCHRONOUS_IO	Asynchronous I/O is supported.
   _POSIX_PRIORITIZED_IO	Prioritized asynchronous I/O is supported.
   _POSIX_SYNCHRONIZED_IO	Synchronizing file data is supported.
   _POSIX_FSYNC			The fsync function is present.
   _POSIX_MAPPED_FILES		Mapping of files to memory is supported.
   _POSIX_MEMLOCK		Locking of all memory is supported.
   _POSIX_MEMLOCK_RANGE		Locking of ranges of memory is supported.
   _POSIX_MEMORY_PROTECTION	Setting of memory protections is supported.
   _POSIX_MESSAGE_PASSING	POSIX.4 message queues are supported.
   _POSIX_SEMAPHORES		POSIX.4 counting semaphores are supported.
   _POSIX_SHARED_MEMORY_OBJECTS	POSIX.4 shared memory objects are supported.
   _POSIX_THREADS		POSIX.1c pthreads are supported.
   _POSIX_THREAD_ATTR_STACKADDR	Thread stack address attribute option supported.
   _POSIX_THREAD_ATTR_STACKSIZE	Thread stack size attribute option supported.
   _POSIX_THREAD_SAFE_FUNCTIONS	Thread-safe functions are supported.
   _POSIX_THREAD_PRIORITY_SCHEDULING
				POSIX.1c thread execution scheduling supported.
   _POSIX_THREAD_PRIO_INHERIT	Thread priority inheritance option supported.
   _POSIX_THREAD_PRIO_PROTECT	Thread priority protection option supported.
   _POSIX_THREAD_PROCESS_SHARED	Process-shared synchronization supported.
   _POSIX_PII			Protocol-independent interfaces are supported.
   _POSIX_PII_XTI		XTI protocol-indep. interfaces are supported.
   _POSIX_PII_SOCKET		Socket protocol-indep. interfaces are supported.
   _POSIX_PII_INTERNET		Internet family of protocols supported.
   _POSIX_PII_INTERNET_STREAM	Connection-mode Internet protocol supported.
   _POSIX_PII_INTERNET_DGRAM	Connectionless Internet protocol supported.
   _POSIX_PII_OSI		ISO/OSI family of protocols supported.
   _POSIX_PII_OSI_COTS		Connection-mode ISO/OSI service supported.
   _POSIX_PII_OSI_CLTS		Connectionless ISO/OSI service supported.
   _POSIX_POLL			Implementation supports `poll' function.
   _POSIX_SELECT		Implementation supports `select' and `pselect'.

   _XOPEN_REALTIME		X/Open realtime support is available.
   _XOPEN_REALTIME_THREADS	X/Open realtime thread support is available.
   _XOPEN_SHM			Shared memory interface according to XPG4.2.

   _XBS5_ILP32_OFF32		Implementation provides environment with 32-bit
				int, long, pointer, and off_t types.
   _XBS5_ILP32_OFFBIG		Implementation provides environment with 32-bit
				int, long, and pointer and off_t with at least
				64 bits.
   _XBS5_LP64_OFF64		Implementation provides environment with 32-bit
				int, and 64-bit long, pointer, and off_t types.
   _XBS5_LPBIG_OFFBIG		Implementation provides environment with at
				least 32 bits int and long, pointer, and off_t
				with at least 64 bits.

   If any of these symbols is defined as -1, the corresponding option is not
   true for any file.  If any is defined as other than -1, the corresponding
   option is true for all files.  If a symbol is not defined at all, the value
   for a specific file can be obtained from `pathconf' and `fpathconf'.

   _POSIX_CHOWN_RESTRICTED	Only the super user can use `chown' to change
				the owner of a file.  `chown' can only be used
				to change the group ID of a file to a group of
				which the calling process is a member.
   _POSIX_NO_TRUNC		Pathname components longer than
				NAME_MAX generate an error.
   _POSIX_VDISABLE		If defined, if the value of an element of the
				`c_cc' member of `struct termios' is
				_POSIX_VDISABLE, no character will have the
				effect associated with that element.
   _POSIX_SYNC_IO		Synchronous I/O may be performed.
   _POSIX_ASYNC_IO		Asynchronous I/O may be performed.
   _POSIX_PRIO_IO		Prioritized Asynchronous I/O may be performed.

   Support for the Large File Support interface is not generally available.
   If it is available the following constants are defined to one.
   _LFS64_LARGEFILE		Low-level I/O supports large files.
   _LFS64_STDIO			Standard I/O supports large files.
   */

#include <bits/posix_opt.h>

/* Get the environment definitions from Unix98.  */
#if defined __USE_UNIX98 || defined __USE_XOPEN2K
# include <bits/environments.h>
#endif

/* Standard file descriptors.  */
#define	STDIN_FILENO	0	/* Standard input.  */
#define	STDOUT_FILENO	1	/* Standard output.  */
#define	STDERR_FILENO	2	/* Standard error output.  */


/* All functions that are not declared anywhere else.  */

#include <bits/types.h>

#ifndef	__ssize_t_defined
typedef __ssize_t ssize_t;
# define __ssize_t_defined
#endif

#define	__need_size_t
#define __need_NULL
#include <stddef.h>

#if defined __USE_XOPEN || defined __USE_XOPEN2K
/* The Single Unix specification says that some more types are
   available here.  */
# ifndef __gid_t_defined
typedef __gid_t gid_t;
#  define __gid_t_defined
# endif

# ifndef __uid_t_defined
typedef __uid_t uid_t;
#  define __uid_t_defined
# endif

# ifndef __off_t_defined
#  ifndef __USE_FILE_OFFSET64
typedef __off_t off_t;
#  else
typedef __off64_t off_t;
#  endif
#  define __off_t_defined
# endif
# if defined __USE_LARGEFILE64 && !defined __off64_t_defined
typedef __off64_t off64_t;
#  define __off64_t_defined
# endif

# ifndef __useconds_t_defined
typedef __useconds_t useconds_t;
#  define __useconds_t_defined
# endif

# ifndef __pid_t_defined
typedef __pid_t pid_t;
#  define __pid_t_defined
# endif
#endif	/* X/Open */

#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
# ifndef __intptr_t_defined
typedef __intptr_t intptr_t;
#  define __intptr_t_defined
# endif
#endif

#if defined __USE_MISC || defined __USE_XOPEN
# ifndef __socklen_t_defined
typedef __socklen_t socklen_t;
#  define __socklen_t_defined
# endif
#endif

/* Values for the second argument to access.
   These may be OR'd together.  */
#define	R_OK	4		/* Test for read permission.  */
#define	W_OK	2		/* Test for write permission.  */
#define	X_OK	1		/* Test for execute permission.  */
#define	F_OK	0		/* Test for existence.  */

/* Test for access to NAME using the real UID and real GID.  */
extern int access (const char *__name, int __type) __THROW __nonnull ((1));

#ifdef __USE_GNU
/* Test for access to NAME using the effective UID and GID
   (as normal file operations use).  */
extern int euidaccess (const char *__name, int __type)
     __THROW __nonnull ((1));

/* An alias for `euidaccess', used by some other systems.  */
extern int eaccess (const char *__name, int __type)
     __THROW __nonnull ((1));
#endif

#ifdef __USE_ATFILE
/* Test for access to FILE relative to the directory FD is open on.
   If AT_EACCESS is set in FLAG, then use effective IDs like `eaccess',
   otherwise use real IDs like `access'.  */
extern int faccessat (int __fd, const char *__file, int __type, int __flag)
     __THROW __nonnull ((2)) __wur;
#endif /* Use GNU.  */


/* Values for the WHENCE argument to lseek.  */
#ifndef	_STDIO_H		/* <stdio.h> has the same definitions.  */
# define SEEK_SET	0	/* Seek from beginning of file.  */
# define SEEK_CUR	1	/* Seek from current position.  */
# define SEEK_END	2	/* Seek from end of file.  */
# ifdef __USE_GNU
#  define SEEK_DATA	3	/* Seek to next data.  */
#  define SEEK_HOLE	4	/* Seek to next hole.  */
# endif
#endif

#if defined __USE_MISC && !defined L_SET
/* Old BSD names for the same constants; just for compatibility.  */
# define L_SET		SEEK_SET
# define L_INCR		SEEK_CUR
# define L_XTND		SEEK_END
#endif


/* Move FD's file position to OFFSET bytes from the
   beginning of the file (if WHENCE is SEEK_SET),
   the current position (if WHENCE is SEEK_CUR),
   or the end of the file (if WHENCE is SEEK_END).
   Return the new file position.  */
#ifndef __USE_FILE_OFFSET64
extern __off_t lseek (int __fd, __off_t __offset, int __whence) __THROW;
#else
# ifdef __REDIRECT_NTH
extern __off64_t __REDIRECT_NTH (lseek,
				 (int __fd, __off64_t __offset, int __whence),
				 lseek64);
# else
#  define lseek lseek64
# endif
#endif
#ifdef __USE_LARGEFILE64
extern __off64_t lseek64 (int __fd, __off64_t __offset, int __whence)
     __THROW;
#endif

/* Close the file descriptor FD.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern int close (int __fd);

/* Read NBYTES into BUF from FD.  Return the
   number read, -1 for errors or 0 for EOF.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t read (int __fd, void *__buf, size_t __nbytes) __wur;

/* Write N bytes of BUF to FD.  Return the number written, or -1.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t write (int __fd, const void *__buf, size_t __n) __wur;

#if defined __USE_UNIX98 || defined __USE_XOPEN2K8
# ifndef __USE_FILE_OFFSET64
/* Read NBYTES into BUF from FD at the given position OFFSET without
   changing the file pointer.  Return the number read, -1 for errors
   or 0 for EOF.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t pread (int __fd, void *__buf, size_t __nbytes,
		      __off_t __offset) __wur;

/* Write N bytes of BUF to FD at the given position OFFSET without
   changing the file pointer.  Return the number written, or -1.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern ssize_t pwrite (int __fd, const void *__buf, size_t __n,
		       __off_t __offset) __wur;
# else
#  ifdef __REDIRECT
extern ssize_t __REDIRECT (pread, (int __fd, void *__buf, size_t __nbytes,
				   __off64_t __offset),
			   pread64) __wur;
extern ssize_t __REDIRECT (pwrite, (int __fd, const void *__buf,
				    size_t __nbytes, __off64_t __offset),
			   pwrite64) __wur;
#  else
#   define pread pread64
#   define pwrite pwrite64
#  endif
# endif

# ifdef __USE_LARGEFILE64
/* Read NBYTES into BUF from FD at the given position OFFSET without
   changing the file pointer.  Return the number read, -1 for errors
   or 0 for EOF.  */
extern ssize_t pread64 (int __fd, void *__buf, size_t __nbytes,
			__off64_t __offset) __wur;
/* Write N bytes of BUF to FD at the given position OFFSET without
   changing the file pointer.  Return the number written, or -1.  */
extern ssize_t pwrite64 (int __fd, const void *__buf, size_t __n,
			 __off64_t __offset) __wur;
# endif
#endif

/* Create a one-way communication channel (pipe).
   If successful, two file descriptors are stored in PIPEDES;
   bytes written on PIPEDES[1] can be read from PIPEDES[0].
   Returns 0 if successful, -1 if not.  */
extern int pipe (int __pipedes[2]) __THROW __wur;

#ifdef __USE_GNU
/* Same as pipe but apply flags passed in FLAGS to the new file
   descriptors.  */
extern int pipe2 (int __pipedes[2], int __flags) __THROW __wur;
#endif

/* Schedule an alarm.  In SECONDS seconds, the process will get a SIGALRM.
   If SECONDS is zero, any currently scheduled alarm will be cancelled.
   The function returns the number of seconds remaining until the last
   alarm scheduled would have signaled, or zero if there wasn't one.
   There is no return value to indicate an error, but you can set `errno'
   to 0 and check its value after calling `alarm', and this might tell you.
   The signal may come late due to processor scheduling.  */
extern unsigned int alarm (unsigned int __seconds) __THROW;

/* Make the process sleep for SECONDS seconds, or until a signal arrives
   and is not ignored.  The function returns the number of seconds less
   than SECONDS which it actually slept (thus zero if it slept the full time).
   If a signal handler does a `longjmp' or modifies the handling of the
   SIGALRM signal while inside `sleep' call, the handling of the SIGALRM
   signal afterwards is undefined.  There is no return value to indicate
   error, but if `sleep' returns SECONDS, it probably didn't work.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern unsigned int sleep (unsigned int __seconds);

#if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
    || defined __USE_MISC
/* Set an alarm to go off (generating a SIGALRM signal) in VALUE
   microseconds.  If INTERVAL is nonzero, when the alarm goes off, the
   timer is reset to go off every INTERVAL microseconds thereafter.
   Returns the number of microseconds remaining before the alarm.  */
extern __useconds_t ualarm (__useconds_t __value, __useconds_t __interval)
     __THROW;

/* Sleep USECONDS microseconds, or until a signal arrives that is not blocked
   or ignored.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern int usleep (__useconds_t __useconds);
#endif


/* Suspend the process until a signal arrives.
   This always returns -1 and sets `errno' to EINTR.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern int pause (void);


/* Change the owner and group of FILE.  */
extern int chown (const char *__file, __uid_t __owner, __gid_t __group)
     __THROW __nonnull ((1)) __wur;

#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
/* Change the owner and group of the file that FD is open on.  */
extern int fchown (int __fd, __uid_t __owner, __gid_t __group) __THROW __wur;


/* Change owner and group of FILE, if it is a symbolic
   link the ownership of the symbolic link is changed.  */
extern int lchown (const char *__file, __uid_t __owner, __gid_t __group)
     __THROW __nonnull ((1)) __wur;

#endif /* Use X/Open Unix.  */

#ifdef __USE_ATFILE
/* Change the owner and group of FILE relative to the directory FD is open
   on.  */
extern int fchownat (int __fd, const char *__file, __uid_t __owner,
		     __gid_t __group, int __flag)
     __THROW __nonnull ((2)) __wur;
#endif /* Use GNU.  */

/* Change the process's working directory to PATH.  */
extern int chdir (const char *__path) __THROW __nonnull ((1)) __wur;

#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
/* Change the process's working directory to the one FD is open on.  */
extern int fchdir (int __fd) __THROW __wur;
#endif

/* Get the pathname of the current working directory,
   and put it in SIZE bytes of BUF.  Returns NULL if the
   directory couldn't be determined or SIZE was too small.
   If successful, returns BUF.  In GNU, if BUF is NULL,
   an array is allocated with `malloc'; the array is SIZE
   bytes long, unless SIZE == 0, in which case it is as
   big as necessary.  */
extern char *getcwd (char *__buf, size_t __size) __THROW __wur;

#ifdef	__USE_GNU
/* Return a malloc'd string containing the current directory name.
   If the environment variable `PWD' is set, and its value is correct,
   that value is used.  */
extern char *get_current_dir_name (void) __THROW;
#endif

#if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
    || defined __USE_MISC
/* Put the absolute pathname of the current working directory in BUF.
   If successful, return BUF.  If not, put an error message in
   BUF and return NULL.  BUF should be at least PATH_MAX bytes long.  */
extern char *getwd (char *__buf)
     __THROW __nonnull ((1)) __attribute_deprecated__ __wur;
#endif


/* Duplicate FD, returning a new file descriptor on the same file.  */
extern int dup (int __fd) __THROW __wur;

/* Duplicate FD to FD2, closing FD2 and making it open on the same file.  */
extern int dup2 (int __fd, int __fd2) __THROW;

#ifdef __USE_GNU
/* Duplicate FD to FD2, closing FD2 and making it open on the same
   file while setting flags according to FLAGS.  */
extern int dup3 (int __fd, int __fd2, int __flags) __THROW;
#endif

/* NULL-terminated array of "NAME=VALUE" environment variables.  */
extern char **__environ;
#ifdef __USE_GNU
extern char **environ;
#endif


/* Replace the current process, executing PATH with arguments ARGV and
   environment ENVP.  ARGV and ENVP are terminated by NULL pointers.  */
extern int execve (const char *__path, char *const __argv[],
		   char *const __envp[]) __THROW __nonnull ((1, 2));

#ifdef __USE_XOPEN2K8
/* Execute the file FD refers to, overlaying the running program image.
   ARGV and ENVP are passed to the new program, as for `execve'.  */
extern int fexecve (int __fd, char *const __argv[], char *const __envp[])
     __THROW __nonnull ((2));
#endif


/* Execute PATH with arguments ARGV and environment from `environ'.  */
extern int execv (const char *__path, char *const __argv[])
     __THROW __nonnull ((1, 2));

/* Execute PATH with all arguments after PATH until a NULL pointer,
   and the argument after that for environment.  */
extern int execle (const char *__path, const char *__arg, ...)
     __THROW __nonnull ((1, 2));

/* Execute PATH with all arguments after PATH until
   a NULL pointer and environment from `environ'.  */
extern int execl (const char *__path, const char *__arg, ...)
     __THROW __nonnull ((1, 2));

/* Execute FILE, searching in the `PATH' environment variable if it contains
   no slashes, with arguments ARGV and environment from `environ'.  */
extern int execvp (const char *__file, char *const __argv[])
     __THROW __nonnull ((1, 2));

/* Execute FILE, searching in the `PATH' environment variable if
   it contains no slashes, with all arguments after FILE until a
   NULL pointer and environment from `environ'.  */
extern int execlp (const char *__file, const char *__arg, ...)
     __THROW __nonnull ((1, 2));

#ifdef __USE_GNU
/* Execute FILE, searching in the `PATH' environment variable if it contains
   no slashes, with arguments ARGV and environment from `environ'.  */
extern int execvpe (const char *__file, char *const __argv[],
		    char *const __envp[])
     __THROW __nonnull ((1, 2));
#endif


#if defined __USE_MISC || defined __USE_XOPEN
/* Add INC to priority of the current process.  */
extern int nice (int __inc) __THROW __wur;
#endif


/* Terminate program execution with the low-order 8 bits of STATUS.  */
extern void _exit (int __status) __attribute__ ((__noreturn__));


/* Get the `_PC_*' symbols for the NAME argument to `pathconf' and `fpathconf';
   the `_SC_*' symbols for the NAME argument to `sysconf';
   and the `_CS_*' symbols for the NAME argument to `confstr'.  */
#include <bits/confname.h>

/* Get file-specific configuration information about PATH.  */
extern long int pathconf (const char *__path, int __name)
     __THROW __nonnull ((1));

/* Get file-specific configuration about descriptor FD.  */
extern long int fpathconf (int __fd, int __name) __THROW;

/* Get the value of the system variable NAME.  */
extern long int sysconf (int __name) __THROW;

#ifdef	__USE_POSIX2
/* Get the value of the string-valued system variable NAME.  */
extern size_t confstr (int __name, char *__buf, size_t __len) __THROW;
#endif


/* Get the process ID of the calling process.  */
extern __pid_t getpid (void) __THROW;

/* Get the process ID of the calling process's parent.  */
extern __pid_t getppid (void) __THROW;

/* Get the process group ID of the calling process.  */
extern __pid_t getpgrp (void) __THROW;

/* Get the process group ID of process PID.  */
extern __pid_t __getpgid (__pid_t __pid) __THROW;
#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
extern __pid_t getpgid (__pid_t __pid) __THROW;
#endif


/* Set the process group ID of the process matching PID to PGID.
   If PID is zero, the current process's process group ID is set.
   If PGID is zero, the process ID of the process is used.  */
extern int setpgid (__pid_t __pid, __pid_t __pgid) __THROW;

#if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
/* Both System V and BSD have `setpgrp' functions, but with different
   calling conventions.  The BSD function is the same as POSIX.1 `setpgid'
   (above).  The System V function takes no arguments and puts the calling
   process in its on group like `setpgid (0, 0)'.

   New programs should always use `setpgid' instead.

   GNU provides the POSIX.1 function.  */

/* Set the process group ID of the calling process to its own PID.
   This is exactly the same as `setpgid (0, 0)'.  */
extern int setpgrp (void) __THROW;

#endif	/* Use misc or X/Open.  */

/* Create a new session with the calling process as its leader.
   The process group IDs of the session and the calling process
   are set to the process ID of the calling process, which is returned.  */
extern __pid_t setsid (void) __THROW;

#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8
/* Return the session ID of the given process.  */
extern __pid_t getsid (__pid_t __pid) __THROW;
#endif

/* Get the real user ID of the calling process.  */
extern __uid_t getuid (void) __THROW;

/* Get the effective user ID of the calling process.  */
extern __uid_t geteuid (void) __THROW;

/* Get the real group ID of the calling process.  */
extern __gid_t getgid (void) __THROW;

/* Get the effective group ID of the calling process.  */
extern __gid_t getegid (void) __THROW;

/* If SIZE is zero, return the number of supplementary groups
   the calling process is in.  Otherwise, fill in the group IDs
   of its supplementary groups in LIST and return the number written.  */
extern int getgroups (int __size, __gid_t __list[]) __THROW __wur;

#ifdef	__USE_GNU
/* Return nonzero iff the calling process is in group GID.  */
extern int group_member (__gid_t __gid) __THROW;
#endif

/* Set the user ID of the calling process to UID.
   If the calling process is the super-user, set the real
   and effective user IDs, and the saved set-user-ID to UID;
   if not, the effective user ID is set to UID.  */
extern int setuid (__uid_t __uid) __THROW __wur;

#if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
/* Set the real user ID of the calling process to RUID,
   and the effective user ID of the calling process to EUID.  */
extern int setreuid (__uid_t __ruid, __uid_t __euid) __THROW __wur;
#endif

#ifdef __USE_XOPEN2K
/* Set the effective user ID of the calling process to UID.  */
extern int seteuid (__uid_t __uid) __THROW __wur;
#endif /* Use POSIX.1-2001.  */

/* Set the group ID of the calling process to GID.
   If the calling process is the super-user, set the real
   and effective group IDs, and the saved set-group-ID to GID;
   if not, the effective group ID is set to GID.  */
extern int setgid (__gid_t __gid) __THROW __wur;

#if defined __USE_MISC || defined __USE_XOPEN_EXTENDED
/* Set the real group ID of the calling process to RGID,
   and the effective group ID of the calling process to EGID.  */
extern int setregid (__gid_t __rgid, __gid_t __egid) __THROW __wur;
#endif

#ifdef __USE_XOPEN2K
/* Set the effective group ID of the calling process to GID.  */
extern int setegid (__gid_t __gid) __THROW __wur;
#endif /* Use POSIX.1-2001.  */

#ifdef __USE_GNU
/* Fetch the real user ID, effective user ID, and saved-set user ID,
   of the calling process.  */
extern int getresuid (__uid_t *__ruid, __uid_t *__euid, __uid_t *__suid)
     __THROW;

/* Fetch the real group ID, effective group ID, and saved-set group ID,
   of the calling process.  */
extern int getresgid (__gid_t *__rgid, __gid_t *__egid, __gid_t *__sgid)
     __THROW;

/* Set the real user ID, effective user ID, and saved-set user ID,
   of the calling process to RUID, EUID, and SUID, respectively.  */
extern int setresuid (__uid_t __ruid, __uid_t __euid, __uid_t __suid)
     __THROW __wur;

/* Set the real group ID, effective group ID, and saved-set group ID,
   of the calling process to RGID, EGID, and SGID, respectively.  */
extern int setresgid (__gid_t __rgid, __gid_t __egid, __gid_t __sgid)
     __THROW __wur;
#endif


/* Clone the calling process, creating an exact copy.
   Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */
extern __pid_t fork (void) __THROWNL;

#if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K8) \
    || defined __USE_MISC
/* Clone the calling process, but without copying the whole address space.
   The calling process is suspended until the new process exits or is
   replaced by a call to `execve'.  Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */
extern __pid_t vfork (void) __THROW;
#endif /* Use misc or XPG < 7. */


/* Return the pathname of the terminal FD is open on, or NULL on errors.
   The returned storage is good only until the next call to this function.  */
extern char *ttyname (int __fd) __THROW;

/* Store at most BUFLEN characters of the pathname of the terminal FD is
   open on in BUF.  Return 0 on success, otherwise an error number.  */
extern int ttyname_r (int __fd, char *__buf, size_t __buflen)
     __THROW __nonnull ((2)) __wur;

/* Return 1 if FD is a valid descriptor associated
   with a terminal, zero if not.  */
extern int isatty (int __fd) __THROW;

#ifdef __USE_MISC
/* Return the index into the active-logins file (utmp) for
   the controlling terminal.  */
extern int ttyslot (void) __THROW;
#endif


/* Make a link to FROM named TO.  */
extern int link (const char *__from, const char *__to)
     __THROW __nonnull ((1, 2)) __wur;

#ifdef __USE_ATFILE
/* Like link but relative paths in TO and FROM are interpreted relative
   to FROMFD and TOFD respectively.  */
extern int linkat (int __fromfd, const char *__from, int __tofd,
		   const char *__to, int __flags)
     __THROW __nonnull ((2, 4)) __wur;
#endif

#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
/* Make a symbolic link to FROM named TO.  */
extern int symlink (const char *__from, const char *__to)
     __THROW __nonnull ((1, 2)) __wur;

/* Read the contents of the symbolic link PATH into no more than
   LEN bytes of BUF.  The contents are not null-terminated.
   Returns the number of characters read, or -1 for errors.  */
extern ssize_t readlink (const char *__restrict __path,
			 char *__restrict __buf, size_t __len)
     __THROW __nonnull ((1, 2)) __wur;
#endif /* Use POSIX.1-2001.  */

#ifdef __USE_ATFILE
/* Like symlink but a relative path in TO is interpreted relative to TOFD.  */
extern int symlinkat (const char *__from, int __tofd,
		      const char *__to) __THROW __nonnull ((1, 3)) __wur;

/* Like readlink but a relative PATH is interpreted relative to FD.  */
extern ssize_t readlinkat (int __fd, const char *__restrict __path,
			   char *__restrict __buf, size_t __len)
     __THROW __nonnull ((2, 3)) __wur;
#endif

/* Remove the link NAME.  */
extern int unlink (const char *__name) __THROW __nonnull ((1));

#ifdef __USE_ATFILE
/* Remove the link NAME relative to FD.  */
extern int unlinkat (int __fd, const char *__name, int __flag)
     __THROW __nonnull ((2));
#endif

/* Remove the directory PATH.  */
extern int rmdir (const char *__path) __THROW __nonnull ((1));


/* Return the foreground process group ID of FD.  */
extern __pid_t tcgetpgrp (int __fd) __THROW;

/* Set the foreground process group ID of FD set PGRP_ID.  */
extern int tcsetpgrp (int __fd, __pid_t __pgrp_id) __THROW;


/* Return the login name of the user.

   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern char *getlogin (void);
#ifdef __USE_POSIX199506
/* Return at most NAME_LEN characters of the login name of the user in NAME.
   If it cannot be determined or some other error occurred, return the error
   code.  Otherwise return 0.

   This function is a possible cancellation point and therefore not
   marked with __THROW.  */
extern int getlogin_r (char *__name, size_t __name_len) __nonnull ((1));
#endif

#ifdef	__USE_MISC
/* Set the login name returned by `getlogin'.  */
extern int setlogin (const char *__name) __THROW __nonnull ((1));
#endif


#ifdef	__USE_POSIX2
/* Get definitions and prototypes for functions to process the
   arguments in ARGV (ARGC of them, minus the program name) for
   options given in OPTS.  */
# include <bits/getopt_posix.h>
#endif


#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K
/* Put the name of the current host in no more than LEN bytes of NAME.
   The result is null-terminated if LEN is large enough for the full
   name and the terminator.  */
extern int gethostname (char *__name, size_t __len) __THROW __nonnull ((1));
#endif


#if defined __USE_MISC
/* Set the name of the current host to NAME, which is LEN bytes long.
   This call is restricted to the super-user.  */
extern int sethostname (const char *__name, size_t __len)
     __THROW __nonnull ((1)) __wur;

/* Set the current machine's Internet number to ID.
   This call is restricted to the super-user.  */
extern int sethostid (long int __id) __THROW __wur;


/* Get and set the NIS (aka YP) domain name, if any.
   Called just like `gethostname' and `sethostname'.
   The NIS domain name is usually the empty string when not using NIS.  */
extern int getdomainname (char *__name, size_t __len)
     __THROW __nonnull ((1)) __wur;
extern int setdomainname (const char *__name, size_t __len)
     __THROW __nonnull ((1)) __wur;


/* Revoke access permissions to all processes currently communicating
   with the control terminal, and then send a SIGHUP signal to the process
   group of the control terminal.  */
extern int vhangup (void) __THROW;

/* Revoke the access of all descriptors currently open on FILE.  */
extern int revoke (const char *__file) __THROW __nonnull ((1)) __wur;


/* Enable statistical profiling, writing samples of the PC into at most
   SIZE bytes of SAMPLE_BUFFER; every processor clock tick while profiling
   is enabled, the system examines the user PC and increments
   SAMPLE_BUFFER[((PC - OFFSET) / 2) * SCALE / 65536].  If SCALE is zero,
   disable profiling.  Returns zero on success, -1 on error.  */
extern int profil (unsigned short int *__sample_buffer, size_t __size,
		   size_t __offset, unsigned int __scale)
     __THROW __nonnull ((1));


/* Turn accounting on if NAME is an existing file.  The system will then write
   a record for each process as it terminates, to this file.  If NAME is NULL,
   turn accounting off.  This call is restricted to the super-user.  */
extern int acct (const char *__name) __THROW;


/* Successive calls return the shells listed in `/etc/shells'.  */
extern char *getusershell (void) __THROW;
extern void endusershell (void) __THROW; /* Discard cached info.  */
extern void setusershell (void) __THROW; /* Rewind and re-read the file.  */


/* Put the program in the background, and dissociate from the controlling
   terminal.  If NOCHDIR is zero, do `chdir ("/")'.  If NOCLOSE is zero,
   redirects stdin, stdout, and stderr to /dev/null.  */
extern int daemon (int __nochdir, int __noclose) __THROW __wur;
#endif /* Use misc.  */


#if defined __USE_MISC || (defined __USE_XOPEN && !defined __USE_XOPEN2K)
/* Make PATH be the root directory (the starting point for absolute paths).
   This call is restricted to the super-user.  */
extern int chroot (const char *__path) __THROW __nonnull ((1)) __wur;

/* Prompt with PROMPT and read a string from the terminal without echoing.
   Uses /dev/tty if possible; otherwise stderr and stdin.  */
extern char *getpass (const char *__prompt) __nonnull ((1));
#endif /* Use misc || X/Open.  */


/* Make all changes done to FD actually appear on disk.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern int fsync (int __fd);


#ifdef __USE_GNU
/* Make all changes done to all files on the file system associated
   with FD actually appear on disk.  */
extern int syncfs (int __fd) __THROW;
#endif


#if defined __USE_MISC || defined __USE_XOPEN_EXTENDED

/* Return identifier for the current host.  */
extern long int gethostid (void);

/* Make all changes done to all files actually appear on disk.  */
extern void sync (void) __THROW;


# if defined __USE_MISC || !defined __USE_XOPEN2K
/* Return the number of bytes in a page.  This is the system's page size,
   which is not necessarily the same as the hardware page size.  */
extern int getpagesize (void)  __THROW __attribute__ ((__const__));


/* Return the maximum number of file descriptors
   the current process could possibly have.  */
extern int getdtablesize (void) __THROW;
# endif

#endif /* Use misc || X/Open Unix.  */


#if defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K8

/* Truncate FILE to LENGTH bytes.  */
# ifndef __USE_FILE_OFFSET64
extern int truncate (const char *__file, __off_t __length)
     __THROW __nonnull ((1)) __wur;
# else
#  ifdef __REDIRECT_NTH
extern int __REDIRECT_NTH (truncate,
			   (const char *__file, __off64_t __length),
			   truncate64) __nonnull ((1)) __wur;
#  else
#   define truncate truncate64
#  endif
# endif
# ifdef __USE_LARGEFILE64
extern int truncate64 (const char *__file, __off64_t __length)
     __THROW __nonnull ((1)) __wur;
# endif

#endif /* Use X/Open Unix || POSIX 2008.  */

#if defined __USE_POSIX199309 \
    || defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K

/* Truncate the file FD is open on to LENGTH bytes.  */
# ifndef __USE_FILE_OFFSET64
extern int ftruncate (int __fd, __off_t __length) __THROW __wur;
# else
#  ifdef __REDIRECT_NTH
extern int __REDIRECT_NTH (ftruncate, (int __fd, __off64_t __length),
			   ftruncate64) __wur;
#  else
#   define ftruncate ftruncate64
#  endif
# endif
# ifdef __USE_LARGEFILE64
extern int ftruncate64 (int __fd, __off64_t __length) __THROW __wur;
# endif

#endif /* Use POSIX.1b || X/Open Unix || XPG6.  */


#if (defined __USE_XOPEN_EXTENDED && !defined __USE_XOPEN2K) \
    || defined __USE_MISC

/* Set the end of accessible data space (aka "the break") to ADDR.
   Returns zero on success and -1 for errors (with errno set).  */
extern int brk (void *__addr) __THROW __wur;

/* Increase or decrease the end of accessible data space by DELTA bytes.
   If successful, returns the address the previous end of data space
   (i.e. the beginning of the new space, if DELTA > 0);
   returns (void *) -1 for errors (with errno set).  */
extern void *sbrk (intptr_t __delta) __THROW;
#endif


#ifdef __USE_MISC
/* Invoke `system call' number SYSNO, passing it the remaining arguments.
   This is completely system-dependent, and not often useful.

   In Unix, `syscall' sets `errno' for all errors and most calls return -1
   for errors; in many systems you cannot pass arguments or get return
   values for all system calls (`pipe', `fork', and `getppid' typically
   among them).

   In Mach, all system calls take normal arguments and always return an
   error code (zero for success).  */
extern long int syscall (long int __sysno, ...) __THROW;

#endif	/* Use misc.  */


#if (defined __USE_MISC || defined __USE_XOPEN_EXTENDED) && !defined F_LOCK
/* NOTE: These declarations also appear in <fcntl.h>; be sure to keep both
   files consistent.  Some systems have them there and some here, and some
   software depends on the macros being defined without including both.  */

/* `lockf' is a simpler interface to the locking facilities of `fcntl'.
   LEN is always relative to the current file position.
   The CMD argument is one of the following.

   This function is a cancellation point and therefore not marked with
   __THROW.  */

# define F_ULOCK 0	/* Unlock a previously locked region.  */
# define F_LOCK  1	/* Lock a region for exclusive use.  */
# define F_TLOCK 2	/* Test and lock a region for exclusive use.  */
# define F_TEST  3	/* Test a region for other processes locks.  */

# ifndef __USE_FILE_OFFSET64
extern int lockf (int __fd, int __cmd, __off_t __len) __wur;
# else
#  ifdef __REDIRECT
extern int __REDIRECT (lockf, (int __fd, int __cmd, __off64_t __len),
		       lockf64) __wur;
#  else
#   define lockf lockf64
#  endif
# endif
# ifdef __USE_LARGEFILE64
extern int lockf64 (int __fd, int __cmd, __off64_t __len) __wur;
# endif
#endif /* Use misc and F_LOCK not already defined.  */


#ifdef __USE_GNU

/* Evaluate EXPRESSION, and repeat as long as it returns -1 with `errno'
   set to EINTR.  */

# define TEMP_FAILURE_RETRY(expression) \
  (__extension__							      \
    ({ long int __result;						      \
       do __result = (long int) (expression);				      \
       while (__result == -1L && errno == EINTR);			      \
       __result; }))

/* Copy LENGTH bytes from INFD to OUTFD.  */
ssize_t copy_file_range (int __infd, __off64_t *__pinoff,
			 int __outfd, __off64_t *__poutoff,
			 size_t __length, unsigned int __flags);
#endif /* __USE_GNU */

#if defined __USE_POSIX199309 || defined __USE_UNIX98
/* Synchronize at least the data part of a file with the underlying
   media.  */
extern int fdatasync (int __fildes);
#endif /* Use POSIX199309 */

#ifdef __USE_MISC
/* One-way hash PHRASE, returning a string suitable for storage in the
   user database.  SALT selects the one-way function to use, and
   ensures that no two users' hashes are the same, even if they use
   the same passphrase.  The return value points to static storage
   which will be overwritten by the next call to crypt.  */
extern char *crypt (const char *__key, const char *__salt)
     __THROW __nonnull ((1, 2));
#endif

#ifdef	__USE_XOPEN
/* Swab pairs bytes in the first N bytes of the area pointed to by
   FROM and copy the result to TO.  The value of TO must not be in the
   range [FROM - N + 1, FROM - 1].  If N is odd the first byte in FROM
   is without partner.  */
extern void swab (const void *__restrict __from, void *__restrict __to,
		  ssize_t __n) __THROW __nonnull ((1, 2));
#endif


/* Prior to Issue 6, the Single Unix Specification required these
   prototypes to appear in this header.  They are also found in
   <stdio.h>.  */
#if defined __USE_XOPEN && !defined __USE_XOPEN2K
/* Return the name of the controlling terminal.  */
extern char *ctermid (char *__s) __THROW;

/* Return the name of the current user.  */
extern char *cuserid (char *__s);
#endif


/* Unix98 requires this function to be declared here.  In other
   standards it is in <pthread.h>.  */
#if defined __USE_UNIX98 && !defined __USE_XOPEN2K
extern int pthread_atfork (void (*__prepare) (void),
			   void (*__parent) (void),
			   void (*__child) (void)) __THROW;
#endif

#ifdef __USE_MISC
/* Write LENGTH bytes of randomness starting at BUFFER.  Return 0 on
   success or -1 on error.  */
int getentropy (void *__buffer, size_t __length) __wur;
#endif

/* Define some macros helping to catch buffer overflows.  */
#if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
# include <bits/unistd.h>
#endif

__END_DECLS

#endif /* unistd.h  */