creat(2)

creat, creat64 -- create a new file or rewrite an existing one

Synopsis

   #include <sys/types.h>
   #include <sys/stat.h>
   #include <fcntl.h>
   
   int creat(const char path, mode_t mode);
   

   int creat64(const char path, mode_t mode);

Description

creat creates a new ordinary file or prepares to rewrite an existing file named by the pathname pointed to by path.

If the file exists, the length is truncated to 0 and the mode and owner are unchanged.

If the file does not exist the file's owner ID is set to the effective user ID of the process. The group ID of the file is set to the effective group ID of the process, or if the S_ISGID bit is set in the parent directory then the group ID of the file is inherited from the parent directory.

The mode bits and Access Control List (ACL) of the file are based on the value of mode, modified as follows:

If the group ID of the new file does not match the effective group ID or one of the supplementary group IDs, the S_ISGID bit is cleared.
All bits set in the process file mode creation mask are cleared (see umask(2)).
The ``save text image after execution bit'' of the mode is cleared (see chmod(2) for the values of mode)
For each default ACL entry in the parent directory's ACL a corresponding ACL entry is created in the new file's ACL. (see acl(2)).

If creat succeeds, it returns a write-only file descriptor and the file is open for writing, even if the mode does not permit writing. The file pointer is set to the beginning of the file. The file descriptor is set to remain open across exec system calls (see fcntl(2)). A new file may be created with a mode that forbids writing.

The call creat(path, mode) is equivalent to:

   	open(path, O_WRONLY | O_CREAT | O_TRUNC, mode)

The call creat64(path, mode) is equivalent to:

   	open(path, O_WRONLY | O_CREAT | O_TRUNC | O_LARGEFILE, mode)

Return values

On success, creat and creat64 return a non-negative integer, namely the lowest numbered unused file descriptor. On failure, creat and creat64 return -1, set errno to identify the error, and no files are created or modified.

In the following condition, creat fails and sets errno to:

EOVERFLOW: The named file is a regular file and the size of the file cannot be represented correctly in an object of type off_t.

In the following conditions, creat and creat64 fail and set errno to:

EACCES: Search permission is denied on a component of the path prefix.
EACCES: The file does not exist and write permission on the directory in which the file is to be created is denied.
EACCES: The file exists and write permission is denied.
EAGAIN: The file exists, mandatory file/record locking is set, and there are outstanding record locks on the file (see chmod(2)).
EFAULT: path points outside the allocated address space of the process.
EINTR: A signal was caught during the creat or creat64 system call.
EISDIR: The named file is an existing directory.
ELOOP: Too many symbolic links were encountered in translating path.
EMFILE: The process has too many open files (see getrlimit(2)).
ENAMETOOLONG: The length of the path argument exceeds {PATH_MAX}, or the length of a path component exceeds {NAME_MAX} while _POSIX_NO_TRUNC is in effect.
ENOTDIR: A component of the path prefix is not a directory.
ENOENT: A component of the path prefix does not exist.
ENOENT: The pathname is null.
EROFS: The named file resides or would reside on a read-only file system.
ETXTBSY: The file is a pure procedure (shared text) file that is being executed.
ENFILE: The system file table is full.
ENOLINK: path points to a remote machine and the link to that machine is no longer active.
EMULTIHOP: Components of path require hopping to multiple remote machines.
ENOSPC: The file system is out of inodes.

References

chmod(2), close(2), dup(2), fcntl(2), getrlimit(2), intro(2), lseek(2), open(2), read(2), stat(5), umask(2), write(2)

Notices

Considerations for threads programming

Open file descriptors are a process resource and available to any sibling thread; if used concurrently, actions by one thread can interfere with those of a sibling.

Considerations for large file support

creat64 supports large files, but is otherwise identical to creat. For details on programming for large file capable applications, see ``Large File Support'' in intro(2).