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.\" Copyright (c) 1983, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)fcntl.2 8.2 (Berkeley) 1/12/94
.\"
.TH FCNTL 2 "15 September 1997" GNO "System Calls"
.SH NAME
.BR fcntl
\- file control
.SH SYNOPSIS
#include <fcntl.h>
.sp 1
int
\fBfcntl\fR (int \fIfd\fR, int \fIcmd\fR, ... /* int \fIarg\fR */ );
.SH DESCRIPTION
.IB "See the " BUGS " section for caveats on the GNO implementation."
.LP
.BR Fcntl
provides for control over descriptors.
The argument
.I fd
is a descriptor to be operated on by
.I cmd
as follows:
.RS
.IP \fBF_DUPFD\fR
Return a new descriptor as follows:
.sp 1
.RS
Lowest numbered available descriptor greater than or equal to
.IR arg .
.sp 1
Same object references as the original descriptor.
.sp 1
New descriptor shares the same file offset if the object
was a file.
.sp 1
Same access mode (read, write or read/write).
.sp 1
Same file status flags (i.e., both file descriptors
share the same file status flags).
.sp 1
The close-on-exec flag associated with the new file descriptor
is set to remain open across
.BR execve (2)
system calls.
.RE
.IP \fBF_GETFD\fR
Get the close-on-exec flag associated with the file descriptor
.IR fd .
If the low-order bit of the returned value is 0,
the file will remain open across
.BR exec ,
otherwise the file will be closed upon execution of
.BR exec
.RI ( arg
is ignored).
.IP \fBF_SETFD\fR
Set the close-on-exec flag associated with
.I fd
to the low order bit of
.I arg
(0 or 1 as above).
.IP \fBF_GETFL\fR
Get descriptor status flags, as described below
.RI ( arg
is ignored).
.IP \fBF_SETFL\fR
Set descriptor status flags to
.IR arg .
.IP \fBF_GETOWN\fB
Get the process ID or process group
currently receiving
.BR SIGIO
and
.BR SIGURG
signals; process groups are returned
as negative values
.RI ( arg
is ignored).
.IP \fBF_SETOWN\fR
Set the process or process group
to receive
.BR SIGIO
and
.BR SIGURG
signals;
process groups are specified by supplying
.I arg
as negative, otherwise
.I arg
is interpreted as a process ID.
.RE
.LP
The flags for the
.BR F_GETFL
and
.BR F_SETFL
flags are as follows:
.RS
.IP \fBO_NONBLOCK\fR
Non-blocking I/O; if no data is available to a
.BR read (2)
call, or if a
.BR write (2)
operation would block,
the read or write call returns -1 with the error
.BR EAGAIN .
.IP \fBO_APPEND\fR
Force each write to append at the end of file;
corresponds to the
.BR O_APPEND
flag of
.BR open (2).
.IP \fBO_ASYNC\fR
Enable the
.BR SIGIO
signal to be sent to the process group
when I/O is possible, e.g.,
upon availability of data to be read.
.RE
.LP
Several commands are available for doing advisory file locking;
they all operate on the following structure:
.nf
struct flock {
off_t l_start; /* starting offset */
off_t l_len; /* len = 0 means until end of file */
pid_t l_pid; /* lock owner */
short l_type; /* lock type: read/write, etc. */
short l_whence; /* type of l_start */
};
.fi
The commands available for advisory record locking are as follows:
.RS
.IP \fBF_GETLK\fR
Get the first lock that blocks the lock description pointed to by the
third argument,
.IR arg ,
taken as a pointer to a
.I "struct flock"
(see above).
The information retrieved overwrites the information passed to
.BR fcntl
in the
.I flock
structure.
If no lock is found that would prevent this lock from being created,
the structure is left unchanged by this function call except for the
lock type which is set to
.BR F_UNLCK .
.IP \fBF_SETLK\fR
Set or clear a file segment lock according to the lock description
pointed to by the third argument,
.IR arg ,
taken as a pointer to a
.I "struct flock"
(see above).
.BR F_SETLK
is used to establish shared (or read) locks
.RB ( F_RDLCK )
or exclusive (or write) locks,
.RB ( F_WRLCK ),
as well as remove either type of lock
.RB ( F_UNLCK ).
If a shared or exclusive lock cannot be set,
.BR fcntl
returns immediately with
.BR EACCES .
.IP \fBF_SETLKW\fR
This command is the same as
.BR F_SETLK
except that if a shared or exclusive lock is blocked by other locks,
the process waits until the request can be satisfied.
If a signal that is to be caught is received while
.BR fcntl
is waiting for a region, the
.BR fcntl
will be interrupted if the signal handler has not specified the
.BR SA_RESTART
(see
.BR sigaction (2)).
.RE
.LP
When a shared lock has been set on a segment of a file,
other processes can set shared locks on that segment
or a portion of it.
A shared lock prevents any other process from setting an exclusive
lock on any portion of the protected area.
A request for a shared lock fails if the file descriptor was not
opened with read access.
.LP
An exclusive lock prevents any other process from setting a shared lock or
an exclusive lock on any portion of the protected area.
A request for an exclusive lock fails if the file was not
opened with write access.
.LP
The value of
.I l_whence
is
.BR SEEK_SET ,
.BR SEEK_CUR ,
or
.BR SEEK_END
to indicate that the relative offset,
.I l_start
bytes, will be measured from the start of the file,
current position, or end of the file, respectively.
The value of
.I l_len
is the number of consecutive bytes to be locked.
If
.I l_len
is negative, the result is undefined.
The
.I l_pid
field is only used with
.BR F_GETLK
to return the process ID of the process holding a blocking lock.
After a successful
.BR F_GETLK
request, the value of
.I l_whence
is
.BR SEEK_SET .
.LP
Locks may start and extend beyond the current end of a file,
but may not start or extend before the beginning of the file.
A lock is set to extend to the largest possible value of the
file offset for that file if
.I l_len
is set to zero. If
.I l_whence
and
.I l_start
point to the beginning of the file, and
.I l_len
is zero, the entire file is locked.
If an application wishes only to do entire file locking, the
.BR flock (2)
system call is much more efficient.
.LP
There is at most one type of lock set for each byte in the file.
Before a successful return from an
.BR F_SETLK
or an
.BR F_SETLKW
request when the calling process has previously existing locks
on bytes in the region specified by the request,
the previous lock type for each byte in the specified
region is replaced by the new lock type.
As specified above under the descriptions
of shared locks and exclusive locks, an
.BR F_SETLK
or an
.BR F_SETLKW
request fails or blocks respectively when another process has existing
locks on bytes in the specified region and the type of any of those
locks conflicts with the type specified in the request.
.LP
This interface follows the completely stupid semantics of System V and
POSIX 1003.1-88
that require that all locks associated with a file for a given process are
removed when \fIany\fP file descriptor for that file is closed by that process.
This semantic means that applications must be aware of any files that
a subroutine library may access.
For example if an application for updating the password file locks the
password file database while making the update, and then calls
.BR getpwnam (3)
to retrieve a record,
the lock will be lost because
.BR getpwnam (3)
opens, reads, and closes the password database.
The database close will release all locks that the process has
associated with the database, even if the library routine never
requested a lock on the database.
Another minor semantic problem with this interface is that
locks are not inherited by a child process created using the
.BR fork (2)
function.
The
.BR flock (2)
interface has much more rational last close semantics and
allows locks to be inherited by child processes.
.BR Flock (2)
is recommended for applications that want to ensure the integrity
of their locks when using library routines or wish to pass locks
to their children.
Note that
.BR flock (2)
and
.BR fcntl (2)
locks may be safely used concurrently.
.LP
All locks associated with a file for a given process are
removed when the process terminates.
.LP
A potential for deadlock occurs if a process controlling a locked region
is put to sleep by attempting to lock the locked region of another process.
This implementation detects that sleeping until a locked region is unlocked
would cause a deadlock and fails with an
.BR EDEADLK
error.
.SH IMPLEMENTATION NOTES
.LP
In the non-threaded library
.BR fcntl
is implemented as the
.IR fcntl
syscall.
.LP
In the threaded library, the
.IR fcntl
syscall is assembled to
.BR _thread_sys_fcntl
and
.BR fcntl
is implemented as a function which disables thread rescheduling, locks
.IR fd
for read and write, then calls
.BR _thread_sys_fcntl .
Before returning,
.BR fcntl
unlocks
.IR fd
and enables thread rescheduling.
.SH RETURN VALUES
Upon successful completion, the value returned depends on
.I cmd
as follows:
.RS
.IP \fBF_DUPFD\fR
A new file descriptor.
.IP \fBF_GETFD\fR
Value of flag (only the low-order bit is defined).
.IP \fBF_GETFL\fR
Value of flags.
.IP \fBF_GETOWN\fR
Value of file descriptor owner.
.IP \fBother\fR
Value other than -1.
.RE
.LP
Otherwise, a value of -1 is returned and
.IR errno
is set to indicate the error.
.SH ERRORS
.BR Fcntl
will fail if:
.RS
.IP \fBEACCES\fR
The argument
.I arg
is
.BR F_SETLK ,
the type of lock
.RI ( l_type )
is a shared lock
.RB ( F_RDLCK )
or exclusive lock
.RB ( F_WRLCK ),
and the segment of a file to be locked is already
exclusive-locked by another process;
or the type is an exclusive lock and some portion of the
segment of a file to be locked is already shared-locked or
exclusive-locked by another process.
.IP \fBEBADF\fR
.I Fildes
is not a valid open file descriptor.
.LP
The argument
.I cmd
is
.BR F_SETLK
or
.BR F_SETLKW ,
the type of lock
.RI ( l_type )
is a shared lock
.RB ( F_RDLCK ),
and
.I fildes
is not a valid file descriptor open for reading.
.LP
The argument
.I cmd
is
.BR F_SETLK
or
.BR F_SETLKW ,
the type of lock
.RI ( l_type )
is an exclusive lock
.RB ( F_WRLCK ),
and
.I fildes
is not a valid file descriptor open for writing.
.IP \fBEDEADLK\fR
The argument
.I cmd
is
.BR F_SETLKW ,
and a deadlock condition was detected.
.IP \fBEINTR\fR
The argument
.I cmd
is
.BR F_SETLKW ,
and the function was interrupted by a signal.
.IP \fBEINVAL\fR
.I Cmd
is
.BR F_DUPFD
and
.I arg
is negative or greater than the maximum allowable number
(see
.BR getdtablesize (2)).
.LP
The argument
.I cmd
is
.BR F_GETLK ,
.BR F_SETLK ,
or
.BR F_SETLKW ,
and the data to which
.I arg
points is not valid, or
.I fildes
refers to a file that does not support locking.
.IP \fBEMFILE\fR
The argument
.I cmd
is
.BR F_DUPFD
and the maximum number of file descriptors permitted for the
process are already in use,
or no file descriptors greater than or equal to
.I arg
are available.
.IP \fBENOLCK\fR
The argument
.I cmd
is
.BR F_SETLK
or
.BR F_SETLKW ,
and satisfying the lock or unlock request would result in the
number of locked regions in the system exceeding a system-imposed limit.
.IP \fBESRCH\fR
.I Cmd
is
.BR F_SETOWN
and
the process ID given as argument is not in use.
.RE
.LP
In addition, if
.I fd
refers to a descriptor open on a terminal device (as opposed to a
descriptor open on a socket), a
.I cmd
of
.BR F_SETOWN
can fail for the same reasons as in
.BR tcsetpgrp (3),
and a
.I cmd
of
.BR F_GETOWN
for the reasons as stated in
.BR tcgetpgrp (3).
.SH BUGS
Currently, the only
.IR cmd s
used by the GNO implementation are
.BR F_DUPFD
and
.BR F_GETFL .
Any other values will result in an error and set errno to
.BR EINVAL .
.SH SEE ALSO
.BR close (2),
.BR execve (2),
.BR flock (2),
.BR getdtablesize (2),
.BR open (2),
.BR sigvec (2),
.BR tcgetpgrp (3),
.BR tcsetpgrp (3)
.SH HISTORY
The
.BR fcntl
function call appeared in 4.2BSD.

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.\" Copyright (c) 1983, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)rename.2 8.1 (Berkeley) 6/4/93
.\"
.TH RENAME 2 "15 September 1997" GNO "System Calls"
.SH NAME
.BR rename
\- change the name of a file
.SH SYNOPSIS
#include <stdio.h>
.sp 1
int \fBrename\fR (const char *\fIfrom\fR, const char *\fIto\fR);
.SH DESCRIPTION
.BR Rename
causes the link named
.I from
to be renamed as
.IR to .
If
.I to
exists, it is first removed.
Both
.I from
and
.I to
must be of the same type (that is, both directories or both
non-directories), and must reside on the same file system.
.LP
.BR Rename
guarantees that an instance of
.I to
will always exist, even if the system should crash in
the middle of the operation.
.LP
If the final component of
.I from
is a symbolic link,
the symbolic link is renamed,
not the file or directory to which it points.
.SH CAVEATS
The system can deadlock if a loop in the file system graph is present.
This loop takes the form of an entry in directory
.IR a ,
say
.IR a/foo ,
being a hard link to directory
.IR b ,
and an entry in
directory
.IR b ,
say
.IR b/bar ,
being a hard link
to directory
.IR a .
When such a loop exists and two separate processes attempt to
perform
\fBrename\fR (\fIa/foo\fR, \fIb/bar\fR)
and
\fBrename\fR (\fIb/bar\fR, \fIa/foo\fR),
respectively,
the system may deadlock attempting to lock
both directories for modification.
Hard links to directories should be
replaced by symbolic links by the system administrator.
.LP
GNO does not currently support symbolic or multiple hard links, so the above
paragraph and the final paragraph of the DESCRIPTION section does not apply.
.SH RETURN VALUES
A 0 value is returned if the operation succeeds, otherwise
.BR rename
returns -1 and the global variable
.IR errno
indicates the reason for the failure.
.SH ERRORS
.BR Rename
will fail and neither of the argument files will be
affected if:
.RS
.IP \fBEINVAL\fR
Either pathname contains a character with the high-order bit set.
.IP \fBENAMETOOLONG\fR
A component of either pathname exceeded 255 characters,
or the entire length of either path name exceeded 1023 characters.
.IP \fBENOENT\fR
A component of the
.I from
path does not exist,
or a path prefix of
.I to
does not exist.
.IP \fBEACCES\fR
A component of either path prefix denies search permission.
.IP \fBEACCES\fR
The requested link requires writing in a directory with a mode
that denies write permission.
.IP \fBEPERM\fR
The directory containing
.I from
is marked sticky,
and neither the containing directory nor
.I from
are owned by the effective user ID.
.IP \fBEPERM\fR
The
.I to
file exists,
the directory containing
.I to
is marked sticky,
and neither the containing directory nor
.I to
are owned by the effective user ID.
.IP \fBELOOP\fR
Too many symbolic links were encountered in translating either pathname.
.IP \fBENOTDIR\fR
A component of either path prefix is not a directory.
.IP \fBENOTDIR\fR
.I from
is a directory, but
.I to
is not a directory.
.IP \fBEISDIR\fR
.I to
is a directory, but
.I from
is not a directory.
.IP \fBEXDEV\fR
The link named by
.I to
and the file named by
.I from
are on different logical devices (file systems). Note that this error
code will not be returned if the implementation permits cross-device
links.
.IP \fBENOSPC\fR
The directory in which the entry for the new name is being placed
cannot be extended because there is no space left on the file
system containing the directory.
.IP \fBEDQUOT\fR
The directory in which the entry for the new name
is being placed cannot be extended because the
user's quota of disk blocks on the file system
containing the directory has been exhausted.
.IP \fBEIO\fR
An I/O error occurred while making or updating a directory entry.
.IP \fBEROFS\fR
The requested link requires writing in a directory on a read-only file
system.
.IP \fBEFAULT\fR
.IR Path
points outside the process's allocated address space.
.IP \fBEINVAL\fR
.I From
is a parent directory of
.IR to ,
or an attempt is made to rename
.BR \&.
or
.BR \&.. .
.IP \fBENOTEMPTY\fR
.I To
is a directory and is not empty.
.RE
.SH SEE ALSO
.BR open (2)
.BR symlink (7)
.SH STANDARDS
.BR Rename
conforms to IEEE Std 1003.1-1988 (POSIX).