1.\" $NetBSD: open.2,v 1.22 2002/02/08 01:28:20 ross Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. All advertising materials mentioning features or use of this software 15.\" must display the following acknowledgement: 16.\" This product includes software developed by the University of 17.\" California, Berkeley and its contributors. 18.\" 4. Neither the name of the University nor the names of its contributors 19.\" may be used to endorse or promote products derived from this software 20.\" without specific prior written permission. 21.\" 22.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 23.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 24.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 25.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 26.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 27.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 28.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 29.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 30.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 31.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 32.\" SUCH DAMAGE. 33.\" 34.\" @(#)open.2 8.2 (Berkeley) 11/16/93 35.\" 36.Dd November 16, 1993 37.Dt OPEN 2 38.Os 39.Sh NAME 40.Nm open 41.Nd open or create a file for reading or writing 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.Fd #include \*[Lt]fcntl.h\*[Gt] 46.Ft int 47.Fn open "const char *path" "int flags" "mode_t mode" 48.Sh DESCRIPTION 49The file name specified by 50.Fa path 51is opened 52for reading and/or writing as specified by the 53argument 54.Fa flags 55and the file descriptor returned to the calling process. 56The 57.Fa flags 58are specified by 59.Em or Ns 'ing 60the following values. 61Applications must specify exactly one of the first three values 62(file access modes): 63.Bl -tag -offset indent -width O_NONBLOCK 64.It Dv O_RDONLY 65Open for reading only. 66.It Dv O_WRONLY 67Open for writing only. 68.It Dv O_RDWR 69Open for reading and writing. 70.El 71.Pp 72Any combination of the following may be used: 73.Bl -tag -offset indent -width O_NONBLOCK 74.It Dv O_NONBLOCK 75Do not block on open or for data to become available. 76.It Dv O_APPEND 77Append to the file on each write. 78.It Dv O_CREAT 79Create the file if it does not exist, in which case the file is 80created with mode 81.Ar mode 82as described in 83.Xr chmod 2 84and modified by the process' umask value (see 85.Xr umask 2 ) . 86.It Dv O_TRUNC 87Truncate size to 0. 88.It Dv O_EXCL 89Error if 90.Dv O_CREAT 91and the file already exists. 92.It Dv O_SHLOCK 93Atomically obtain a shared lock. 94.It Dv O_EXLOCK 95Atomically obtain an exclusive lock. 96.It Dv O_DSYNC 97If set, write operations will be performed according to synchronized 98I/O data integrity completion: 99each write will wait for the file data to be committed to stable 100storage. 101.It Dv O_SYNC 102If set, write operations will be performed according to synchronized 103I/O file integrity completion: 104each write will wait for both the file data and file status to be 105committed to stable storage. 106.It Dv O_RSYNC 107If set, read operations will complete at the same level of 108integrity which is in effect for write operations: 109if specified together with 110.Dv O_SYNC , 111each read will wait for the file status to be committed to stable 112storage. 113.Pp 114Combining 115.Dv O_RSYNC 116with 117.Dv O_DSYNC 118only, or specifying it without any other synchronized I/O integrity 119completion flag set, has no further effect. 120.El 121.Pp 122Opening a file with 123.Dv O_APPEND 124set causes each write on the file 125to be appended to the end. 126If 127.Dv O_TRUNC 128is specified and the 129file exists, the file is truncated to zero length. 130.Pp 131If 132.Dv O_EXCL 133is set with 134.Dv O_CREAT 135and the file already 136exists, 137.Fn open 138returns an error. 139This may be used to implement a simple exclusive access locking mechanism. 140If 141.Dv O_EXCL 142is set and the last component of the pathname is 143a symbolic link, 144.Fn open 145will fail even if the symbolic 146link points to a non-existent name. 147.Pp 148If the 149.Dv O_NONBLOCK 150flag is specified, do not wait for the device or file to be ready or 151available. 152If the 153.Fn open 154call would result 155in the process being blocked for some reason (e.g., waiting for 156carrier on a dialup line), 157.Fn open 158returns immediately. 159This flag also has the effect of making all subsequent I/O on the open file non-blocking. 160.Pp 161When opening a file, a lock with 162.Xr flock 2 163semantics can be obtained by setting 164.Dv O_SHLOCK 165for a shared lock, or 166.Dv O_EXLOCK 167for an exclusive lock. 168If creating a file with 169.Dv O_CREAT , 170the request for the lock will never fail 171(provided that the underlying filesystem supports locking). 172.Pp 173If successful, 174.Fn open 175returns a non-negative integer, termed a file descriptor. 176It returns -1 on failure. 177The file pointer used to mark the current position within the 178file is set to the beginning of the file. 179.Pp 180When a new file is created it is given the group of the directory 181which contains it. 182.Pp 183The new descriptor is set to remain open across 184.Xr execve 2 185system calls; see 186.Xr close 2 187and 188.Xr fcntl 2 . 189.Pp 190The system imposes a limit on the number of file descriptors 191open simultaneously by one process. 192Calling 193.Xr getdtablesize 3 194returns the current system limit. 195.Sh ERRORS 196The named file is opened unless: 197.Bl -tag -width Er 198.It Bq Er ENOTDIR 199A component of the path prefix is not a directory. 200.It Bq Er ENAMETOOLONG 201A component of a pathname exceeded 202.Dv {NAME_MAX} 203characters, or an entire path name exceeded 204.Dv {PATH_MAX} 205characters. 206.It Bq Er ENOENT 207.Dv O_CREAT 208is not set and the named file does not exist, or 209a component of the path name that must exist does not exist. 210.It Bq Er EACCES 211Search permission is denied for a component of the path prefix, 212the required permissions (for reading and/or writing) 213are denied for the given flags, or 214.Dv O_CREAT 215is specified, 216the file does not exist, 217and the directory in which it is to be created 218does not permit writing. 219.It Bq Er ELOOP 220Too many symbolic links were encountered in translating the pathname. 221.It Bq Er EISDIR 222The named file is a directory, and the arguments specify 223it is to be opened for writing. 224.It Bq Er EROFS 225The named file resides on a read-only file system, 226and the file is to be modified. 227.It Bq Er EMFILE 228The process has already reached its limit for open file descriptors. 229.It Bq Er ENFILE 230The system file table is full. 231.It Bq Er ENXIO 232The named file is a character special or block 233special file, and the device associated with this special file 234does not exist, or 235the named file is a 236.Tn FIFO , 237.Dv O_NONBLOCK 238and 239.Dv O_WRONLY 240is set and no process has the file open for reading. 241.It Bq Er EINTR 242The 243.Fn open 244operation was interrupted by a signal. 245.It Bq Er EOPNOTSUPP 246.Dv O_SHLOCK 247or 248.Dv O_EXLOCK 249is specified but the underlying filesystem does not support locking. 250.It Bq Er ENOSPC 251.Dv O_CREAT 252is specified, 253the file does not exist, 254and the directory in which the entry for the new file is being placed 255cannot be extended because there is no space left on the file 256system containing the directory. 257.It Bq Er ENOSPC 258.Dv O_CREAT 259is specified, 260the file does not exist, 261and there are no free inodes on the file system on which the 262file is being created. 263.It Bq Er EDQUOT 264.Dv O_CREAT 265is specified, 266the file does not exist, 267and the directory in which the entry for the new file 268is being placed cannot be extended because the 269user's quota of disk blocks on the file system 270containing the directory has been exhausted. 271.It Bq Er EDQUOT 272.Dv O_CREAT 273is specified, 274the file does not exist, 275and the user's quota of inodes on the file system on 276which the file is being created has been exhausted. 277.It Bq Er EIO 278An I/O error occurred while making the directory entry or 279allocating the inode for 280.Dv O_CREAT . 281.It Bq Er ETXTBSY 282The file is a pure procedure (shared text) file that is being 283executed and the 284.Fn open 285call requests write access. 286.It Bq Er EFAULT 287.Fa path 288points outside the process's allocated address space. 289.It Bq Er EEXIST 290.Dv O_CREAT 291and 292.Dv O_EXCL 293were specified and the file exists. 294.It Bq Er EOPNOTSUPP 295An attempt was made to open a socket (not currently implemented). 296.El 297.Sh SEE ALSO 298.Xr chmod 2 , 299.Xr close 2 , 300.Xr dup 2 , 301.Xr lseek 2 , 302.Xr read 2 , 303.Xr umask 2 , 304.Xr write 2 , 305.Xr getdtablesize 3 306.Sh STANDARDS 307The 308.Fn open 309function conforms to 310.St -p1003.1-90 . 311The 312.Fa flags 313values 314.Dv O_DSYNC , 315.Dv O_SYNC 316and 317.Dv O_RSYNC 318are extensions defined in 319.St -p1003.1b-93 . 320.Sh HISTORY 321An 322.Fn open 323function call appeared in 324.At v6 . 325