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The file
name specified by is opened for reading and/or writing as specified by
the argument and the file descriptor returned to the calling process. The
argument may indicate the file is to be created if it does not exist (by
specifying the flag), in which case the file is created with mode as
described in and modified by the process’ umask value (see The flags
specified are formed by the following values 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 create and file exists O_SHLOCK atomically obtain a shared
lock O_EXLOCK atomically obtain an exclusive lock Opening a file with
set causes each write on the file to be appended to the end. If is specified
and the file exists, the file is truncated to zero length. If is set with
and the file already exists, returns an error. This may be used to implement
a simple exclusive access locking mechanism. If is set and the last component
of the pathname is a symbolic link, will fail even if the symbolic link
points to a non-existent name. If the flag is specified, do not wait for
the device or file to be ready or available. If the call would result
in the process being blocked for some reason (e.g., waiting for carrier on
a dialup line), returns immediately. This flag also has the effect of making
all subsequent I/O on the open file non-blocking. When opening a file, a
lock with semantics can be obtained by setting for a shared lock, or
for an exclusive lock. If creating a file with the request for the lock
will never fail (provided that the underlying filesystem supports locking).
If successful, 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. When a new file is
created it is given the group of the directory which contains it. The new
descriptor is set to remain open across system calls; see and The system
imposes a limit on the number of file descriptors open simultaneously by
one process. returns the current system limit.
The named file is opened
unless: A component of the path prefix is not a directory. A component
of a pathname exceeded characters, or an entire path name exceeded
characters. is not set and the named file does not exist. A component
of the path name that must exist does not exist. Search permission is denied
for a component of the path prefix. The required permissions (for reading
and/or writing) are denied for the given flags. is specified, the file
does not exist, and the directory in which it is to be created does not
permit writing. Too many symbolic links were encountered in translating
the pathname. The named file is a directory, and the arguments specify
it is to be opened for writing. The named file resides on a read-only file
system, and the file is to be modified. The process has already reached
its limit for open file descriptors. The system file table is full. The
named file is a character special or block special file, and the device
associated with this special file does not exist. The operation was interrupted
by a signal. or is specified but the underlying filesystem does not support
locking. 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. is specified,
the file does not exist, and there are no free inodes on the file system
on which the file is being created. 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. 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. An I/O error occurred while making the directory
entry or allocating the inode for The file is a pure procedure (shared
text) file that is being executed and the call requests write access.
points outside the process’s allocated address space. and were specified
and the file exists. An attempt was made to open a socket (not currently
implemented).
An function call appeared in
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