NAME

open − open a file for reading or writing, or create a new file

SYNOPSIS

#include <sys/file.h>

open(path, flags, mode)
char ∗path;
int flags, mode;

DESCRIPTION

Open opens the file name for reading and/or writing, as specified by the flags argument and returns a descriptor for that file.  The flags argument may indicate the file is to be created if it does not already exist (by specifying the FCREATE flag), in which case the file is created with mode mode as described in chmod(2) and modified by the process’ umask value (see umask(2)).

Name is the address of a string of ascii characters representing a path name, terminated by a null character.  The flags specified are formed by or’ing the following values

 O_RDONLYopen for reading only
 O_WRONLYopen for writing only
 O_RDWRopen for reading and writing
 O_APPENDappend on each write
 O_CREATcreate file if it does not exist
 O_TRUNCtruncate size to 0
 O_XUSEapply advisory exclusive lock

The above flags are compatible with the /usr/group standard system.  The following additional flags are available in 4.1c:

 FSHLOCK0x008apply advisory shared lock
 FNDELAY0x800do not block on open

Opening a file with O_APPEND set causes each write on the file to be appended to the end.  If O_TRUNC is specified and the file exists, the file is truncated to zero length.  The O_EXLOCK and FSHLOCK flags allow an advisory lock to be applied, see flock(2). If the FNDELAY flag is specified and the open call would result in the process being blocked for some reason (for example, on an advisory lock), the open returns immediately with the error EWOULDBLOCK.

Upon successful completion, a non-negative integer, the file descriptor, is returned.  The file pointer used to mark the current position within the file is set to the beginning of the file. 

The new descriptor is set to remain open across execve system calls; see close(2).

No process may have more than {OPEN_MAX} file descriptors open simultaneously. 

ERRORS

The named file is opened unless one or more of the following are true:

[EPERM] The path argument contained a byte with the high-order bit set. 

[ENOTDIR] A component of the path prefix is not a directory. 

[EINVAL] The O_TRUNC flag was specified, but O_WRITE or O_RDWR was not specified. 

[ENOENT] FCREAT is not set and the named file does not exist. 

[EACCES] A component of the path prefix denies search permission. 

[EACCES] The required permissions (for reading and/or writing) are denied for the named flag. 

[EISDIR] The named file is a directory, and the arguments specify it is to be opened for writting. 

[EROFS] The named file resides on a read-only file system, and the file is to be modified. 

[EMFILE] {OPEN_MAX} file descriptors are currently open. 

[ENXIO] The named file is a character special or block special file, and the device associated with this special file does not exist. 

[ETXTBSY] The file is a pure procedure (shared text) file that is being executed and the open call requests write access. 

[EFAULT] Path points outside the process’s allocated address space. 

[ELOOP] Too many symbolic links were encountered in translating the pathname. 

[EEXIST] The file is to be created for exclusive use and it already exists. 

[ENXIO] The FNDELAY flag is given, and the file is a communications device on which their is no carrier present. 

SEE ALSO

chmod(2), close(2), dup(2), lseek(2), read(2), write(2), umask(2)

BUGS

The implementation of this call needs to be carefully checked

Sun System Release 0.3  —  1 April 1983