.\" $NetBSD: open.2,v 1.8 1995/02/27 12:35:14 cgd Exp $ .\" .\" Copyright (c) 1980, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. All advertising materials mentioning features or use of this software .\" must display the following acknowledgement: .\" This product includes software developed by the University of .\" California, Berkeley and its contributors. .\" 4. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .\" @(#)open.2 8.2 (Berkeley) 11/16/93 .\" .Dd November 16, 1993 .Dt OPEN 2 .Os BSD 4 .Sh NAME .Nm open .Nd open or create a file for reading or writing .Sh SYNOPSIS .\" OH??? .Fd #include .Fd #include .Ft int .Fo open .Fa "const char *path" .Fa "int oflag" .Fa "..." .Fc .Sh DESCRIPTION The file name specified by .Fa path is opened for reading and/or writing, as specified by the argument .Fa oflag ; the file descriptor is returned to the calling process. .Pp The .Fa oflag argument may indicate that the file is to be created if it does not exist (by specifying the .Dv O_CREAT flag). In this case, .Nm requires a third argument .Fa "mode_t mode" ; the file is created with mode .Fa mode as described in .Xr chmod 2 and modified by the process' umask value (see .Xr umask 2 ) . .Pp The flags specified are formed by .Em or Ns 'ing the following values: .Pp .Bd -literal -offset indent -compact O_RDONLY open for reading only O_WRONLY open for writing only O_RDWR open for reading and writing O_NONBLOCK do not block on open or for data to become available O_APPEND append on each write O_CREAT create file if it does not exist O_TRUNC truncate size to 0 O_EXCL error if O_CREAT and the file exists O_SHLOCK atomically obtain a shared lock O_EXLOCK atomically obtain an exclusive lock O_NOFOLLOW do not follow symlinks O_SYMLINK allow open of symlinks .Ed .Pp Opening a file with .Dv O_APPEND set causes each write on the file to be appended to the end. If .Dv O_TRUNC is specified and the file exists, the file is truncated to zero length. If .Dv O_EXCL is set with .Dv O_CREAT and the file already exists, .Fn open returns an error. This may be used to implement a simple exclusive-access locking mechanism. If .Dv O_EXCL is set and the last component of the pathname is a symbolic link, .Fn open will fail even if the symbolic link points to a non-existent name. .Pp If the .Dv O_NONBLOCK flag is specified, do not wait for the device or file to be ready or available. If the .Fn open call would result in the process being blocked for some reason (e.g., waiting for carrier on a dialup line), .Fn open returns immediately. This flag also has the effect of making all subsequent I/O on the open file non-blocking. .Pp When opening a file, a lock with .Xr flock 2 semantics can be obtained by setting .Dv O_SHLOCK for a shared lock, or .Dv O_EXLOCK for an exclusive lock. If creating a file with .Dv O_CREAT , the request for the lock will never fail (provided that the underlying filesystem supports locking). .Pp If .Dv O_NOFOLLOW is used in the mask and the target file passed to .Fn open is a symbolic link then the .Fn open will fail. .Pp If .Dv O_SYMLINK is used in the mask and the target file passed to .Fn open is a symbolic link then the .Fn open will be for the symbolic link itself, not what it links to. .Pp If successful, .Fn open returns a non-negative integer, termed a file descriptor. It returns -1 on failure. The file pointer (used to mark the current position within the file) is set to the beginning of the file. .Pp When a new file is created, it is given the group of the directory which contains it. .Pp The new descriptor is set to remain open across .Xr execve system calls; see .Xr close 2 and .Xr fcntl 2 . .Pp The system imposes a limit on the number of file descriptors that can be held open simultaneously by one process. .Xr Getdtablesize 2 returns the current system limit. .Sh RETURN VALUES If successful, .Fn open returns a non-negative integer, termed a file descriptor. It returns -1 on failure, and sets .Va errno to indicate the error. .Sh ERRORS The named file is opened unless: .Bl -tag -width Er .\" =========== .It Bq Er EACCES Search permission is denied for a component of the path prefix. .\" =========== .It Bq Er EACCES The required permissions (for reading and/or writing) are denied for the given flags. .\" =========== .It Bq Er EACCES .Dv O_CREAT is specified, the file does not exist, and the directory in which it is to be created does not permit writing. .\" =========== .It Bq Er EACCES .Dv O_TRUNC is specified and write permission is denied. .\" =========== .It Bq Er EAGAIN .Fa path specifies the slave side of a locked pseudo-terminal device. .\" =========== .It Bq Er EDQUOT .Dv O_CREAT is specified, the file does not exist, and the directory in which the entry for the new file is being placed cannot be extended because the user's quota of disk blocks on the file system containing the directory has been exhausted. .\" =========== .It Bq Er EDQUOT .Dv O_CREAT is specified, the file does not exist, and the user's quota of inodes on the file system on which the file is being created has been exhausted. .\" =========== .It Bq Er EEXIST .Dv O_CREAT and .Dv O_EXCL are specified and the file exists. .\" =========== .It Bq Er EFAULT .Fa Path points outside the process's allocated address space. .\" =========== .It Bq Er EINTR The .Fn open operation is interrupted by a signal. .\" =========== .It Bq Er EINVAL The value of .Fa oflag is not valid. .\" =========== .It Bq Er EIO An I/O error occurs while making the directory entry or allocating the inode for .Dv O_CREAT . .\" =========== .It Bq Er EISDIR The named file is a directory, and the arguments specify that it is to be opened for writing. .\" =========== .It Bq Er ELOOP Too many symbolic links are encountered in translating the pathname. This is taken to be indicative of a looping symbolic link. .\" =========== .It Bq Er EMFILE The process has already reached its limit for open file descriptors. .\" =========== .It Bq Er ENAMETOOLONG A component of a pathname exceeds .Dv {NAME_MAX} characters, or an entire path name exceeded .Dv {PATH_MAX} characters. .\" =========== .It Bq Er ENFILE The system file table is full. .\" =========== .It Bq Er ELOOP .Dv O_NOFOLLOW was specified and the target is a symbolic link. .\" =========== .It Bq Er ENOENT .Dv O_CREAT is not set and the named file does not exist. .\" =========== .It Bq Er ENOENT A component of the path name that must exist does not exist. .\" =========== .It Bq Er ENOSPC .Dv O_CREAT is specified, the file does not exist, and the directory in which the entry for the new file is being placed cannot be extended because there is no space left on the file system containing the directory. .\" =========== .It Bq Er ENOSPC .Dv O_CREAT is specified, the file does not exist, and there are no free inodes on the file system on which the file is being created. .\" =========== .It Bq Er ENOTDIR A component of the path prefix is not a directory. .\" =========== .It Bq Er ENXIO The named file is a character-special or block-special file and the device associated with this special file does not exist. .\" =========== .It Bq Er ENXIO O_NONBLOCK and O_WRONLY are set, the file is a FIFO, and no process has it open for reading. .\" =========== .It Bq Er EOPNOTSUPP .Dv O_SHLOCK or .Dv O_EXLOCK is specified, but the underlying filesystem does not support locking. .\" =========== .It Bq Er EOPNOTSUPP An attempt is made to open a socket (not currently implemented). .\" =========== .It Bq Er EOVERFLOW The named file is a regular file and its size does not fit in an object of type off_t. .\" =========== .It Bq Er EROFS The named file resides on a read-only file system, and the file is to be modified. .\" =========== .It Bq Er ETXTBSY The file is a pure procedure (shared text) file that is being executed and the .Fn open call requests write access. .El .Sh COMPATIBILITY .Fn open on a terminal device (i.e., /dev/console) will now make that device a controlling terminal for the process. Use the O_NOCTTY flag to open a terminal device without changing your controlling terminal. .Sh SEE ALSO .Xr chmod 2 , .Xr close 2 , .Xr dup 2 , .Xr getdtablesize 2 , .Xr lseek 2 , .Xr read 2 , .Xr umask 2 , .Xr write 2 .Sh HISTORY An .Fn open function call appeared in .At v6 .