.TH OPEN 2 2/13/83 .SH NAME open \- open a file for reading or writing, or create a new file .SH SYNOPSIS .nf .ft B #include <sys/file.h> .PP .ft B open(path, flags, mode) char *path; int flags, mode; .fi .SH DESCRIPTION .I Open opens the file .I name for reading and/or writing, as specified by the .I flags argument and returns a descriptor for that file. The .I 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 .I mode as described in .IR chmod (2) and modified by the process' umask value (see .IR umask (2)). .PP .I 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 .IR or 'ing the following values .PP .RS FRDONLY open for reading only FWRONLY open for writing only FRDWR open for reading and writing FAPPEND append on each write FCREATE create file if it does not exist FTRUNCATE truncate size to 0 FEXLOCK apply advisory exclusive lock FSHLOCK apply advisory shared lock FNBLOCK do not block on open .RE .PP Opening a file with FAPPEND set causes each write on the file to be appended to the end. If FTRUNCATE is specified and the file exists, the file is truncated to zero length. The FEXLOCK and FSHLOCK flags allow an advisory lock to be applied, see .IR flock (2). If the FNBLOCK flag is specified and the open call would result in the process being blocked for some reason (e.g. on an advisory lock), the open returns immediately with the error EWOULDBLOCK. .PP 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. .PP The new descriptor is set to remain open across .IR execve system calls; see .IR close (2). .PP No process may have more than {OPEN_MAX} file descriptors open simultaneously. .SH "ERRORS The named file is opened unless on or more of the following are true: .TP 15 [EPERM] The pathname contains a non-ASCII byte. .TP 15 [ENOTDIR] A component of the path prefix is not a directory. .TP 15 [EINVAL] The FTRUNCATE flag was specified, but FWRONLY or FRDWR was not specified. .TP 15 [ENOENT] FCREATE is not set and the named file does not exist. .TP 15 [EACCES] A component of the path previx denies search permission. .TP 15 [EACCES] The required permissions (for reading and/or writing) are denied for the named flag. .TP 15 [EISDIR] The named file is a directory, and the arguments specify it is to be opened for writting. .TP 15 [EROFS] The named file resides on a read-only file system, and the file is to be modified. .TP 15 [EMFILE] {OPEN_MAX} file descriptors are currently open. .TP 15 [ENXIO] The named file is a character special or block special file, and the device associated with this special file does not exist. .TP 15 [ETXTBSY] The file is a pure procedure (shared text) file that is being executed and the \fIopen\fP call requests write access. .TP 15 [EFAULT] .I Path points outside the process's allocated address space. .TP 15 [ELOOP] Too many symbolic links were encountered in translating the pathname. .TP 15 [EEXIST] The file is to be created for exclusive use and it already exists. .TP 15 [ENXIO] The FNBLOCK flag is given, and the file is a communications device on which their is no carrier present. .SH "SEE ALSO" chmod(2), close(2), dup(2), lseek(2), read(2), write(2), umask(2) .SH BUGS The implementation of this call needs to be carefully checked. The flag names and locking facilities are incompatible with the /usr/group standard.