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FCNTL(2)

 NAME

     fcntl - file and descriptor control

 C SYNOPSIS

     #include <unistd.h>
     #include <fcntl.h>

     int fcntl (int fildes, int cmd, ... /* arg */);

 DESCRIPTION

     fcntl provides for control over open descriptors.  fildes is an open
     descriptor obtained from a creat, open, dup, fcntl, pipe, socket, or
     socketpair system call.

     The commands available are:

     F_DUPFD   Return a new descriptor as follows:

               Lowest numbered available descriptor greater than or equal to
               the third argument, arg, taken as an object of type int.

               Refers to the same object as the original descriptor.

               Same file pointer as the original file (i.e., both file
               descriptors share one file pointer).

               Same access mode (read, write or read/write).

               Same descriptor status flags (i.e., both descriptors share the
               same status flags).

               Shares any locks associated with the original file descriptor.

               The close-on-exec flag, FD_CLOEXEC associated with the new
               descriptor is cleared to keep the file open across calls to the
               exec(2) family of functions.

     F_GETFD   Get the file descriptor flags associated with the descriptor
               fildes.  If the FD_CLOEXEC flag is 0 the descriptor will remain
               open across exec, otherwise the descriptor will be closed upon
               execution of exec.

     F_SETFD   Set the file descriptor flags for fildes.  Currently the only
               flag implemented is FD_CLOEXEC.  Note: this flag is a per-
               process and per-descriptor flag; setting or clearing it for a
               particular descriptor will not affect the flag on descriptors
               copied from it by a dup(2) or F_DUPFD operation, nor will it
               affect the flag on other processes instances of that
               descriptor.

     F_GETFL   Get file status flags and file access modes.  The file access
               modes may be extracted from the return value using the mask
               O_ACCMODE.

     F_SETFL   Set file status flags to the third argument, arg, taken as an
               object of type int.  Only the following flags can be set [see
               fcntl(5)]:  FAPPEND, FSYNC, DSYNC, RSYNC, FNDELAY, FNONBLK,
               FLCFLUSH, FLCINVAL, FDIRECT, and FASYNC.  Since arg is used as
               a bit vector to set the flags, values for all the flags must be
               specified in arg.  (Typically, arg may be constructed by
               obtaining existing values by F_GETFL and then changing the
               particular flags.)  FAPPEND is equivalent to O_APPEND; FSYNC is
               equivalent to O_SYNC; FDSYNC is equivalent to O_DSYNC; FRSYNC
               is equivalent to O_RSYNC; FNDELAY is equivalent to O_NDELAY;
               FNONBLK is equivalent to O_NONBLOCK; FLCFLUSH is equivalent to
               O_LCFLUSH; FLCINVAL is equivalent to O_LCINVAL; and FDIRECT is
               equivalent to O_DIRECT.  FASYNC is equivalent to calling ioctl
               with the FIOASYNC command (except that with ioctl all flags
               need not be specified).  This enables the SIGIO facilities and
               is currently supported only on sockets.

               Since the descriptor status flags are shared with descriptors
               copied from a given descriptor by a dup(2) or F_DUPFD
               operation, and by other processes instances of that descriptor
               a F_SETFL operation will affect those other descriptors and
               other instances of the given descriptors as well.  For example,
               setting or clearing the FNDELAY flag will logically cause an
               FIONBIO ioctl(2) to be performed on the object referred to by
               that descriptor.  Thus all descriptors referring to that object
               will be affected.

               Flags not understood for a particular descriptor are silently
               ignored except for FDIRECT. FDIRECT will return EINVAL if used
               on other than an EFS, XFS or BDS file system file. In Irix
               6.5.24 and beyond, remote NFS Version 3 file systems also
               support FDIRECT operation.

     F_FREESP  Alter storage space associated with a section of the ordinary
               file fildes.  The section is specified by a variable of data
               type struct flock pointed to by the third argument arg.  The
               data type struct flock is defined in the <fcntl.h> header file
               [see fcntl(5)] and contains the following members:  l_whence is
               0, 1, or 2 to indicate that the relative offset l_start will be
               measured from the start of the file, the current position, or
               the end of the file, respectively.  l_start is the offset from
               the position specified in l_whence.  l_len is the size of the
               section.  An l_len of 0 frees up to the end of the file; in
               this case, the end of file (i.e., file size) is set to the
               beginning of the section freed.  Any data previously written
               into this section is no longer accessible.  If the section
               specified is beyond the current end of file, the file is grown
               and filled with zeroes.  The l_len field is currently ignored,
               and should be set to 0.

     F_ALLOCSP This command is identical to F_FREESP.

     F_FREESP64
               This command is identical to F_FREESP except that the type of
               the data referred to by the third argument arg is a struct
               flock64.  In this version of the structure, l_start and l_len
               are of type off64_t instead of off_t (64 bits instead of 32
               bits).

     F_ALLOCSP64
               This command is identical to F_FREESP64.

     F_FSSETDM Set the di_dmevmask and di_dmstate fields in an XFS on-disk
               inode.  The only legitimate values for these fields are those
               previously returned in the bs_dmevmask and bs_dmstate fields of
               the bulkstat structure.  The data referred to by the third
               argument arg is a struct fsdmidata.  This structure's members
               are fsd_dmevmask and fsd_dmstate.  The di_dmevmask field is set
               to the value in fsd_dmevmask.  The di_dmstate field is set to
               the value in fsd_dmstate.  This command is restricted to root
               or to processes with device management capabilities.  Its sole
               purpose is to allow backup and restore programs to restore the
               aforementioned critical on-disk inode fields.

     F_DIOINFO Get information required to perform direct I/O on the specified
               fildes.  Direct I/O is performed directly to and from a user's
               data buffer. Since the kernels buffer cache is no longer
               between the two, the user's data buffer must conform to the
               same type of constraints as required for accessing a raw disk
               partition.  The third argument, arg, points to a data type
               struct dioattr which is defined in the <fcntl.h> header file
               and contains the following members: d_mem is the memory
               alignment requirement of the user's data buffer. d_miniosz
               specifies block size, minimum I/O request size, and I/O
               alignment.  The size of all I/O requests must be a multiple of
               this amount and the value of the seek pointer at the time of
               the I/O request must also be an integer multiple of this
               amount.  d_maxiosz is the maximum I/O request size which can be
               performed on the fildes.  If an I/O request does not meet these
               constraints, the read(2) or write(2) will return with EINVAL.
               In IRIX 6.5.19 and beyond, the alignment requirement has been
               relaxed to allow for 512 byte sizes.  It is, however, still
               strongly recommended that the alignment values returned by
               F_DIOINFO be used for performance and for portability to older
               IRIX systems.  All I/O requests are kept consistent with any
               data brought into the cache with an access through a non-direct
               I/O file descriptor.  See also F_SETFL above and open (2).

     F_GETOWN  Used by sockets: get the process ID or process group currently
               receiving SIGIO and SIGURG signals; process groups are returned
               as negative values.

     F_SETOWN  Used by sockets: set the process or process group to receive
               SIGIO and SIGURG signals; process groups are specified by
               supplying arg as negative, otherwise arg is interpreted as a
               process ID.

     F_CLOSEM  Close all file descriptors greater than or equal to fildes.

     F_FSGETXATTR
               Get additional attributes associated with files in XFS file
               systems.  The arg points to a variable of type struct fsxattr.
               The structure fields include:  fsx_xflags (extended flag bits),
               fsx_extsize (nominal extent size in file system blocks),
               fsx_nextents (number of data extents in the file).  A
               fsx_extsize value returned indicates that a preferred extent
               size was previously set on the file, a fsx_extsize of 0
               indicates that the defaults for that filesystem will be used.
               Currently the meaningful bits for the fsx_xflags field are:
               Bit 0 (0x1) - XFS_XFLAG_REALTIME
                         The file is a realtime file.
               Bit 1 (0x2) - XFS_XFLAG_PREALLOC
                         The file has preallocated space.
               Bit 7 (0x80) - XFS_XFLAG_NODUMP
                         The file should be skipped by backup utilities.
               Bit 8 (0x100) - XFS_XFLAG_RTINHERIT
                         Realtime inheritance bit - new files created in the
                         directory will be automatically realtime, and new
                         directories created in the directory will inherit the
                         inheritance bit.
               Bit 9 (0x200) - XFS_XFLAG_PROJINHERIT
                         New files created in the directory will have the
                         project ID of the directory, and new directories
                         created in the directory will inherit the inheritance
                         bit.
               Bit 10 (0x400) - XFS_XFLAG_NOSYMLINKS
                         Symbolic links cannot be created in a directory with
                         this bit set.
               Bit 31 (0x80000000) - XFS_XFLAG_HASATTR
                         The file has extended attributes associated with it.
     F_FSGETXATTRA
          Identical to F_FSGETXATTR except that the fsx_nextents field
          contains the number of attribute extents in the file.

     F_FSSETXATTR
          Set additional attributes associated with files in XFS file systems.
          The arg points to a variable of type struct fsxattr, but only the
          following fields are used in this call:  fsx_xflags and fsx_extsize.
          The fsx_xflags realtime file bit, and the file's extent size, may be
          changed only when the file is empty.

     F_GETBMAP
          Get the block map for a segment of a file in an XFS file system.
          The arg points to an array of variables of type struct getbmap.  All
          sizes and offsets in the structure are in units of 512 bytes.  The
          structure fields include:  bmv_offset (file offset of segment),
          bmv_block (starting block of segment), bmv_length (length of
          segment), bmv_count (number of array entries, including the first),
          and bmv_entries (number of entries filled in).  The first structure
          in the array is a header, and the remaining structures in the array
          contain block map information on return.  The header controls
          iterative calls to the F_GETBMAP command.  The caller fills in the
          bmv_offset and bmv_length fields of the header to indicate the area
          of interest in the file, and fills in the bmv_count field to
          indicate the length of the array.  If the bmv_length value is set to
          -1 then the length of the interesting area is the rest of the file.
          On return from a call, the header is updated so that the command can
          be used again to obtain more information, without re-initializing
          the structures.  Also on return, the bmv_entries field of the header
          is set to the number of array entries actually filled in.  The non-
          header structures will be filled in with bmv_offset, bmv_block, and
          bmv_length. If a region of the file has no blocks (is a hole in the
          file) then the bmv_block field is set to -1.

     F_GETBMAPA
          Identical to F_GETBMAP except that information about the attribute
          fork of the file is returned.

     F_RESVSP
          This command is used to allocate space to a file.  A range of bytes
          is specified with the struct flock.  The blocks are allocated, but
          not zeroed, and the file size does not change.  It is only supported
          on XFS and BDS filesystems.  If the XFS filesystem is configured to
          flag unwritten file extents, performance will be negatively affected
          when writing to preallocated space, since extra filesystem
          transactions are required to convert extent flags on the range of
          the file written.  If xfs_growfs(1M) with the -n option reports
          unwritten=1, then the filesystem was made to flag unwritten extents.
          Only the root user is permitted to execute xfs_growfs(1M).

     F_RESVSP64
          This command is identical to F_RESVSP except that the type of the
          data referred to by the third argument arg is a struct flock64.  In
          this version of the structure, l_start and l_len are of type off64_t
          instead of off_t (64 bits instead of 32 bits).

     F_UNRESVSP
          This command is used to free space from a file.  A range of bytes is
          specified with the struct flock.  Partial filesystem blocks are
          zeroed, and whole filesystem blocks are removed from the file.  The
          file size does not change.  It is only supported on XFS and BDS
          filesystems.

     F_UNRESVSP64
          This command is identical to F_UNRESVSP except that the type of the
          data referred to by the third argument arg is a struct flock64.  In
          this version of the structure, l_start and l_len are of type off64_t
          instead of off_t (64 bits instead of 32 bits).

     F_FSYNC
          fsync data in a range of an ordinary file fildes.  The section is
          specified by a variable of data type struct flock pointed to by the
          third argument arg.  The data type struct flock is defined in the
          <fcntl.h> header file [see fcntl(5)].  If field l_type is set to 1,
          the call behaves like fdatasync(2).  If field l_type is set to 0,
          the call behaves like fsync(2).  fdatasync(2) syncs only the inode
          state required to ensure that the data is permanently on the disk.
          fsync(2) syncs everything that fdatasync(2) flushes but also syncs
          out the other state associated with the file such as the current
          timestamps, permissions, owner, etc.  l_start specifies the start of
          the range in the file to be sync'ed.  l_len specifies the size of
          the range.  A l_len of 0 flushes everything up to the end of the
          file.  The remaining fields are ignored and should be set to 0.

     F_FSYNC64
          This command is identical to F_FSYNC except that the type of the
          data referred to by the third argument arg is a struct flock64.  In
          this version of the structure, l_start and l_len are of type off64_t
          instead of off_t (64 bits instead of 32 bits).

     F_GETBIOSIZE
          This command gets information about the preferred buffered I/O size
          used by the system when performing buffered I/O (e.g. standard Unix
          non-direct I/O) to and from the file.  The information is passed
          back in a structure of type struct biosize pointed to by the third
          argument arg.  The data type struct biosize is defined in the
          <fcntl.h> header file [see fcntl(5)].  biosize lengths are expressed
          in log base 2.  That is if the value is 14, then the true size is
          2^14 (2 raised to the 14th power).  The biosz_read field will
          contain the current value used by the system when reading from the
          file.  Except at the end-of-file, the system will read from the file
          in multiples of this length.  The biosz_write field will contain the
          current value used by the system when writing to the file.  Except
          at the end-of-file, the system will write to the file in multiples
          of this length.  The dfl_biosz_read and dfl_biosz_write will be set
          to the system default values for the opened file.  The biosz_flags
          field will be set to 1 if the current read or write value has been
          explicitly set.  The F_GETBIOSIZE fcntl is supported only on XFS
          filesystems.

     F_SETBIOSIZE
          This command the preferred buffered I/O size used by the system when
          performing buffered I/O (e.g. standard Unix non-direct I/O) to and
          from the file.  The information is passed in a structure of type
          struct biosize pointed to by the third argument arg.  Using smaller
          preferred I/O sizes can result in performance improvements if the
          file is typically accessed using small synchronous I/Os or if only a
          small amount of the file is accessed using small random I/Os,
          resulting in little or no use of the additional data read in near
          the random I/Os.

          To explicitly set the preferred I/O sizes, the biosz_flags field
          should be set to 0 and the biosz_read and biosz_write fields should
          be set to the log base 2 of the desired read and write lengths,
          respectively (e.g. 13 for 8K bytes, 14 for 16K bytes, 15 for 32K
          bytes, etc.).  Valid values are 13-16 inclusive for machines with a
          4K byte pagesize and 14-16 for machines with a 16K byte pagesize.
          The specified read and write values must also result in lengths that
          are greater than or equal to the filesystem block size.  The
          dfl_biosz_read and dfl_biosz_write fields are ignored.

          If biosizes have already been explicitly set due to a prior use of
          F_SETBIOSIZE, and the requested sizes are larger then the existing
          sizes, the fcntl call will return successfully and the system will
          use the smaller of the two sizes.  However, if biosz_flags is set to
          1, the system will use the new values regardless of whether the new
          sizes are larger or smaller than the old.

          To reset the biosize values to the defaults for the filesystem that
          the file resides in, the biosz_flags filed should be set to 2.  The
          remainder of the fields will be ignored in that case.

          Changes made by F_SETBIOSIZE are transient.  The sizes are reset to
          the default values once the reference count on the file drops to
          zero (e.g. all open file descriptors to that file have been closed).
          See fstab(4) for details on how to set the default biosize values
          for a filesystem.  The F_SETBIOSIZE fcntl is supported only on XFS
          filesystems.

     The following commands are used for record-locking.  Locks may be placed
     on an entire file or on segments of a file.

     F_GETLK   Get the first lock which blocks the lock description given by
               the variable of type struct flock pointed to by arg.  The
               information retrieved overwrites the information passed to
               fcntl in the flock structure.  If no lock is found that would
               prevent this lock from being created, then the structure is
               passed back unchanged except that the lock type will be set to
               F_UNLCK and the l_whence field will be set to SEEK_SET.  If a
               lock is found that would prevent this lock from being created,
               then the structure is overwritten with a description of the
               first lock that is preventing such a lock from being created.
               The returned structure will also contain the process ID and the
               system ID of the process holding the lock.  This command never
               creates a lock; it tests whether a particular lock could be
               created.

     F_SETLK   Set or clear a file segment lock according to the variable of
               type struct flock pointed to by arg [see fcntl(5)].  The cmd
               F_SETLK is used to establish read (F_RDLCK) and write (F_WRLCK)
               locks, as well as remove either type of lock (F_UNLCK).  If a
               read or write lock cannot be set fcntl will return immediately
               with an error value of -1.

     F_SETLKW  This cmd is the same as F_SETLK except that if a read or write
               lock is blocked by other locks, the process will sleep until
               the segment is free to be locked.

     F_GETLK64 This cmd is identical to F_GETLK but uses a struct flock64
               instead of a struct flock (see F_FREESP64 above).

     F_SETLK64 This cmd is identical to F_SETLK but uses a struct flock64
               instead of a struct flock.

     F_SETLKW64
               This cmd is identical to F_SETLKW but uses a struct flock64
               instead of a struct flock.

     F_SETBSDLK
               This cmd is identical to F_SETLK and provided for the backward
               compatibility only. Newer applications should use F_SETLK
               instead.

     F_SETBSDLKW
               This cmd is identical to F_SETLKW and provided for the backward
               compatibility only. Newer applications should use F_SETLKW
               instead.

     F_RSETLK  Used  by the network lock daemon, lockd(3N), to communicate
               with the NFS server kernel to handle locks on NFS files.

     F_RSETLKW Used  by the network lock daemon, lockd(3N), to communicate
               with the NFS server kernel to handle locks on NFS files.

     F_RGETLK  Used  by the network lock daemon, lockd(3N), to communicate
               with the NFS server kernel to handle locks on NFS files.

     F_CHKFL   This flag is used internally by F_SETFL to check the legality
               of file flag changes.

     A read lock prevents any process from write locking the protected area.
     More than one read lock may exist for a given segment of a file at a
     given time.  The file descriptor on which a read lock is being placed
     must have been opened with read access.

     A write lock prevents any process from read locking or write locking the
     protected area.  Only one write lock and no read locks may exist for a
     given segment of a file at a given time.  The file descriptor on which a
     write lock is being placed must have been opened with write access.

     The structure flock describes the type (l_type), starting offset
     (l_whence), relative offset (l_start), size (l_len), process id (l_pid),
     and system id (l_sysid) of the segment of the file to be affected.  The
     process id and system id fields are used only with the F_GETLK cmd to
     return the values for a blocking lock.  Locks may start and extend beyond
     the current end of a file, but may not be negative relative to the
     beginning of the file.  A lock may be set to always extend to the end of
     file by setting l_len to zero (0).  If such a lock also has l_whence and
     l_start set to zero (0), the whole file will be locked.  Changing or
     unlocking a segment from the middle of a larger locked segment leaves two
     smaller segments for either end.  Locking a segment that is already
     locked by the calling process causes the old lock type to be removed and
     the new lock type to take effect.  All locks associated with a file for a
     given process are removed when a file descriptor for that file is closed
     by that process or the process holding that file descriptor terminates.
     Locks are not inherited by a child process in a fork(2) system call.

     When file locking is used in conjunction with memory-mapped files over
     NFS, the smallest locking granularity which will work properly with
     multiple clients is the page size of the system.  All clients must use
     the same granularity.

     When mandatory file and record locking is active on a file, [see
     chmod(2)], read(2), creat(2), open(2), and write(2) system calls issued
     on the file will be affected by the record locks in effect.

     The following commands are used for SMB opportunistic locks.  An SMB
     server application will register oplocks on files and grant them to SMB
     clients.  When external references are made to oplocked files, the SMB
     server is notified to revoke the oplocks granted to clients before
     operations from the external references are allowed to continue.

     F_OPLKREG The oplock registration command identifies the file to oplock
               and, via arg, the write side of the pipe (e.g. p[1] from the
               pipe(int *p) call) to use as the signaling mechanism.  The same
               write side pipe can be used for any number of oplocked files.

               If any external references to the file already exist or the
               caller already has an oplock on the file, the F_OPLKREG command
               fails with EAGAIN.  If successful, the value of OP_EXCLUSIVE is
               returned.

     F_OPLKSTAT
               The oplock state change command is used to get state change
               information on any recently externally referenced files
               registered with the given write side pipe (eg p[1] from a
               pipe(int *p) call).  The returned oplock_stat_t structure
               pointed at by arg contains the current state (os_state) and the
               dev/ino information (os_dev/os_ino) to identify the file.

               This is only done on the write side of a pipe for which
               select() indicates there is a byte of data to read() on the
               read side.  A byte of data must then be read() from the read
               side of the pipe for each successful F_OPLKSTAT run on the
               write side for select() to again give proper notification.

               External references that cause state change notification will
               hang for a while until the SMB server acknowledges the
               revocation (typically after revoking the oplock it granted to
               the SMB client) or until the systunable oplock_timeout expires.

     F_OPLKACK The oplock acknowledgement command is primarily used to respond
               to oplock state changes due to external references on the given
               file.  The value given by arg can be OP_REVOKE to revoke the
               oplock either voluntarily or as an acknowledgement of a state
               change reported in an F_OPLKSTAT command, or it can be -1 to
               request the current state of the given file.

               If F_OPLKACK is not used to voluntarily revoke the oplock, the
               oplock is automatically revoked on the SMB server's last
               close() of the file.

               If F_OPLKACK is not used to revoke the oplock in response to a
               state change indicated in an F_OPLKSTAT command, the oplock is
               automatically revoked when the oplock_timeout expires.

     fcntl will fail if one or more of the following are true:

     [EACCES]       cmd is F_SETLK, the type of lock (l_type) is a read lock (
                    F_RDLCK, ) and the segment of a file to be lock is already
                    write locked by another process, or the type is a write
                    lock ( F_WRLOCK, ) and the segment of a file to be locked
                    in already read or write locked by another process.

     [EBADF]        Fildes is not a valid open file descriptor.

     [EBADF]        cmd is F_SETLK, or SETLKW, the type of lock (l_type) is a
                    read lock (F_RDLCK), and fildes is not a valid file
                    descriptor open for reading.

     [EBADF]        cmd is F_SETLK, or SETLKW, the type of lock (l_type) is a
                    write lock (F_WRLCK), and fildes is not a valid file
                    descriptor open for writing.

     [EBADF]        cmd is F_FREESP and fildes is not a valid file descriptor
                    open for writing.

     [EBADF]        cmd is F_OPLOCKREG and the file is not a regular file or
                    the arg is not the write side of a pipe.

     [EMFILE]       cmd is F_DUPFD and {OPEN_MAX} file descriptors are
                    currently in use by this process, or no file descriptors
                    greater than or equal to arg are available.

     [EINVAL]       cmd is F_DUPFD.  arg is either negative, or greater than
                    or equal to the maximum number of open file descriptors
                    allowed each user [see getdtablesize(2)].

     [EINVAL]       cmd is F_GETLK, F_SETLK, or F_SETLKW and arg or the data
                    it points to is not valid.

     [EINVAL]       cmd is F_SETFL, arg includes FDIRECT and is being
                    performed on other than an EFS, XFS, BDS or NFS Version 3
                    file system file.

     [EINVAL]       cmd is F_SETBIOSIZE and arg is invalid.

     [EINVAL]       cmd is F_OPLKREG and fildes is a file in a filesystem
                    other than XFS.  Kernel level oplocks are only supported
                    for XFS.

     [EINVAL]       cmd is F_OPLKACK and the arg is not OP_REVOKE or -1.

     [EAGAIN]       cmd is F_FREESP , the file exists, mandatory file/record
                    locking is set, and there are outstanding record locks on
                    the file.  This restriction is not currently enforced.

     [EAGAIN]       cmd is F_SETLK or F_SETLKW , mandatory file locking bit is
                    set for the file, and the file is currently being mapped
                    to virtual memory via mmap [see mmap(2)].  This
                    restriction is not currently enforced.

     [EAGAIN]       cmd is F_OPLKREG and there is more than one reference on
                    the file.  Oplocks thus cannot be used to guarantee
                    exclusive access to the file.

     [EAGAIN]       cmd is F_OPLKSTAT and there are no state change messages
                    for the specified write side pipe.

     [EPERM]        cmd is F_OPLKREG or F_OPLKSTAT or F_OPLKACK and the user
                    is not superuser.

     [ENOLCK]       cmd is F_SETLK or F_SETLKW, the type of lock is a read or
                    write lock, and there are no more record locks available
                    (too many file segments locked) because the system maximum
                    {FLOCK_MAX} [see intro(2)], has been exceeded.  This can
                    also occur if the object of the lock resides on a remote
                    system and the requisite locking daemons are not
                    configured in both the local and the remote systems.  In
                    particular, if lockd(1M) is running but statd(1M) is not,
                    this error will be returned.  An additional source for
                    this error is when statd(1M) is running but cannot be
                    contacted.  This can occur when the address for the local
                    host cannot be determined.  [See lockd(1M) and statd(1M).]

     [EINTR]        cmd is F_SETLKW and a signal interrupted the process while
                    it was waiting for the lock to be granted.

     [EDEADLK]      cmd is F_SETLKW, the lock is blocked by some lock from
                    another process, and putting the calling-process to sleep,
                    waiting for that lock to become free, would cause a
                    deadlock.

     [EDEADLK]      cmd is F_FREESP, mandatory record locking is enabled,
                    O_NDELAY and O_NONBLOCK are being clear and a deadlock
                    condition was detected.

     [EFAULT]       cmd is F_FREESP, and the value pointed to by the third
                    argument arg resulted in an address outside the process's
                    allocated address space.

     [EFAULT]       cmd is F_GETLK, F_SETLK or F_SETLKW, and arg points
                    outside the program address space.

     [ESRCH]        cmd is F_SETOWN and no process can be found corresponding
                    to that specified by arg.

     [EIO]          An I/O error occurred while reading from or writing to the
                    file system.

     [EOVERFLOW]    cmd is F_GETLK and the process ID of the process holding
                    the requested lock is too large to be stored in the l_pid
                    field.

     [ETIMEDOUT]    The object of the fcntl is located on a remote system
                    which is not available [see intro(2)].

 SEE ALSO

     lockd(1M), close(2), creat(2), dup(2), exec(2), fork(2),
     getdtablesize(2), intro(2), open(2), pipe(2), fcntl(5).

 DIAGNOSTICS

     Upon successful completion, the value returned depends on cmd as follows:
          F_DUPFD   A new file descriptor.
          F_GETFD   Value of flag (only the low-order bit is defined).
          F_SETFD   Value other than -1.
          F_GETFL   Value of file flags.
          F_SETFL   Value other than -1.
          F_FREESP  Value of 0.
          F_ALLOCSP Value of 0.
          F_FREESP64
                    Value of 0.
          F_ALLOCSP64
                    Value of 0.
          F_DIOINFO Value of 0.

          F_GETOWN  pid of socket owner.
          F_SETOWN  Value other than -1.
          F_FSGETXATTR
                    Value of 0.
          F_FSSETXATTR
                    Value of 0.
          F_GETBMAP Value of 0.
          F_RESVSP  Value of 0.
          F_RESVSP64
                    Value of 0.
          F_UNRESVSP
                    Value of 0.
          F_UNRESVSP64
                    Value of 0.
          F_GETLK   Value other than -1.
          F_SETLK   Value other than -1.
          F_SETLKW  Value other than -1.
          F_GETLK64 Value other than -1.
          F_SETLK64 Value other than -1.
          F_SETLKW64
                    Value other than -1.
     Otherwise, a value of -1 is returned and errno is set to indicate the
     error.




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