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The file descriptor returned by a successful call will be the lowest-numbered file descriptor not currently open for the process. By default, the new file descriptor is set to remain open across an execve 2 i. The file offset is set to the beginning of the file see lseek 2. A call to open creates a new open file description, an entry in the system-wide table of open files. A file descriptor is a reference to one of these entries; this reference is unaffected if pathname is subsequently removed or modified to refer to a different file.
The new open file description is initially not shared with any other process, but sharing may arise via fork 2. The file status flags are all of the remaining flags listed below.
The distinction between these two groups of flags is that the file status flags can be retrieved and in some cases modified using fcntl 2. Before each write 2 , the file offset is positioned at the end of the file, as if with lseek 2.
This feature is only available for terminals, pseudoterminals, sockets, and since Linux 2. See fcntl 2 for further details. The owner user ID of the file is set to the effective user ID of the process. The group ownership group ID is set either to the effective group ID of the process or to the group ID of the parent directory depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount 8.
In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. A semantically similar but deprecated interface for block devices is described in raw 8. This flag is Linux-specific, and was added in kernel version 2. When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open fails regardless of where the symbolic link points to.
There is one exception: on Linux 2. If the block device is in use by the system e. If link 2 returns 0, the lock is successful. Otherwise, use stat 2 on the unique file to check if its link count has increased to 2, in which case the lock is also successful. This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity.
This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time. Symbolic links in earlier components of the pathname will still be followed. Neither the open nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait.
For the handling of FIFOs named pipes , see also fifo 7. Any write 2 s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware. Some of these optional flags can be altered using fcntl 2 after the file has been opened. Return Value open and creat return the new file descriptor, or -1 if an error occurred in which case, errno is set appropriately.
Errors EACCES The requested access to the file is not allowed, or search permission is denied for one of the directories in the path prefix of pathname, or the file did not exist yet and write access to the parent directory is not allowed.
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