The Open Group Base Specifications Issue 7
IEEE Std 1003.1-2008, 2016 Edition
Copyright © 2001-2016 The IEEE and The Open Group


fattach - attach a STREAMS-based file descriptor to a file in the file system name space (STREAMS)


[OB XSR] [Option Start] #include <stropts.h>

int fattach(int
fildes, const char *path); [Option End]


The fattach() function shall attach a STREAMS-based file descriptor to a file, effectively associating a pathname with fildes. The application shall ensure that the fildes argument is a valid open file descriptor associated with a STREAMS file. The path argument points to a pathname of an existing file. The application shall have appropriate privileges or be the owner of the file named by path and have write permission. A successful call to fattach() shall cause all pathnames that name the file named by path to name the STREAMS file associated with fildes, until the STREAMS file is detached from the file. A STREAMS file can be attached to more than one file and can have several pathnames associated with it.

The attributes of the named STREAMS file shall be initialized as follows: the permissions, user ID, group ID, and times are set to those of the file named by path, the number of links is set to 1, and the size and device identifier are set to those of the STREAMS file associated with fildes. If any attributes of the named STREAMS file are subsequently changed (for example, by chmod()), neither the attributes of the underlying file nor the attributes of the STREAMS file to which fildes refers shall be affected.

File descriptors referring to the underlying file, opened prior to an fattach() call, shall continue to refer to the underlying file.


Upon successful completion, fattach() shall return 0. Otherwise, -1 shall be returned and errno set to indicate the error.


The fattach() function shall fail if:

Search permission is denied for a component of the path prefix, or the process is the owner of path but does not have write permissions on the file named by path.
The fildes argument is not a valid open file descriptor.
The file named by path is currently a mount point or has a STREAMS file attached to it.
A loop exists in symbolic links encountered during resolution of the path argument.
The length of a component of a pathname is longer than {NAME_MAX}.
A component of path does not name an existing file or path is an empty string.
A component of the path prefix names an existing file that is neither a directory nor a symbolic link to a directory, or the path argument contains at least one non- <slash> character and ends with one or more trailing <slash> characters.
The effective user ID of the process is not the owner of the file named by path and the process does not have appropriate privileges.

The fattach() function may fail if:

The fildes argument does not refer to a STREAMS file.
More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.
The length of a pathname exceeds {PATH_MAX}, or pathname resolution of a symbolic link produced an intermediate result with a length that exceeds {PATH_MAX}.
A link to a file on another file system was attempted.

The following sections are informative.


Attaching a File Descriptor to a File

In the following example, fd refers to an open STREAMS file. The call to fattach() associates this STREAM with the file /tmp/named-STREAM, such that any future calls to open /tmp/named-STREAM, prior to breaking the attachment via a call to fdetach(), will instead create a new file handle referring to the STREAMS file associated with fd.

#include <stropts.h>
    int fd;
    char *pathname = "/tmp/named-STREAM";
    int ret;

ret = fattach(fd, pathname);


The fattach() function behaves similarly to the traditional mount() function in the way a file is temporarily replaced by the root directory of the mounted file system. In the case of fattach(), the replaced file need not be a directory and the replacing file is a STREAMS file.


The file attributes of a file which has been the subject of an fattach() call are specifically set because of an artifact of the original implementation. The internal mechanism was the same as for the mount() function. Since mount() is typically only applied to directories, the effects when applied to a regular file are a little surprising, especially as regards the link count which rigidly remains one, even if there were several links originally and despite the fact that all original links refer to the STREAM as long as the fattach() remains in effect.


The fattach() function may be removed in a future version.


fdetach, isastream

XBD <stropts.h>


First released in Issue 4, Version 2.

Issue 5

Moved from X/OPEN UNIX extension to BASE.

The [EXDEV] error is added to the list of optional errors in the ERRORS section.

Issue 6

This function is marked as part of the XSI STREAMS Option Group.

The normative text is updated to avoid use of the term "must" for application requirements.

The wording of the mandatory [ELOOP] error condition is updated, and a second optional [ELOOP] error condition is added.

Issue 7

Austin Group Interpretation 1003.1-2001 #143 is applied.

The fattach() function is marked obsolescent.

The [ENOTDIR] error condition is clarified to cover the condition where the last component of a pathname exists but is not a directory or a symbolic link to a directory.

POSIX.1-2008, Technical Corrigendum 1, XSH/TC1-2008/0111 [146,324] and XSH/TC1-2008/0112 [291] are applied.

End of informative text.


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