1FCNTL(2)                   Linux Programmer's Manual                  FCNTL(2)
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NAME

6       fcntl - manipulate file descriptor
7

SYNOPSIS

9       #include <unistd.h>
10       #include <fcntl.h>
11
12       int fcntl(int fd, int cmd, ... /* arg */ );
13

DESCRIPTION

15       fcntl() performs one of the operations described below on the open file
16       descriptor fd.  The operation is determined by cmd.
17
18       fcntl() can take an optional third argument.  Whether or not this argu‐
19       ment  is  required is determined by cmd.  The required argument type is
20       indicated in parentheses after  each  cmd  name  (in  most  cases,  the
21       required  type  is  long,  and  we identify the argument using the name
22       arg), or void is specified if the argument is not required.
23
24   Duplicating a file descriptor
25       F_DUPFD (long)
26              Find the lowest numbered available file descriptor greater  than
27              or  equal to arg and make it be a copy of fd.  This is different
28              from dup2(2), which uses exactly the descriptor specified.
29
30              On success, the new descriptor is returned.
31
32              See dup(2) for further details.
33
34       F_DUPFD_CLOEXEC (long; since Linux 2.6.24)
35              As for F_DUPFD, but additionally set the close-on-exec flag  for
36              the  duplicate  descriptor.  Specifying this flag permits a pro‐
37              gram to avoid an additional fcntl() F_SETFD operation to set the
38              FD_CLOEXEC flag.  For an explanation of why this flag is useful,
39              see the description of O_CLOEXEC in open(2).
40
41   File descriptor flags
42       The following commands manipulate the  flags  associated  with  a  file
43       descriptor.   Currently, only one such flag is defined: FD_CLOEXEC, the
44       close-on-exec flag.  If the FD_CLOEXEC bit is 0,  the  file  descriptor
45       will remain open across an execve(2), otherwise it will be closed.
46
47       F_GETFD (void)
48              Read the file descriptor flags; arg is ignored.
49
50       F_SETFD (long)
51              Set the file descriptor flags to the value specified by arg.
52
53   File status flags
54       Each  open  file  description has certain associated status flags, ini‐
55       tialized by open(2) and possibly modified by fcntl().  Duplicated  file
56       descriptors  (made with dup(2), fcntl(F_DUPFD), fork(2), etc.) refer to
57       the same open file description, and thus share  the  same  file  status
58       flags.
59
60       The file status flags and their semantics are described in open(2).
61
62       F_GETFL (void)
63              Read the file status flags; arg is ignored.
64
65       F_SETFL (long)
66              Set  the  file status flags to the value specified by arg.  File
67              access mode (O_RDONLY, O_WRONLY, O_RDWR) and file creation flags
68              (i.e.,  O_CREAT,  O_EXCL, O_NOCTTY, O_TRUNC) in arg are ignored.
69              On Linux this command can only  change  the  O_APPEND,  O_ASYNC,
70              O_DIRECT, O_NOATIME, and O_NONBLOCK flags.
71
72   Advisory locking
73       F_GETLK,  F_SETLK  and  F_SETLKW are used to acquire, release, and test
74       for the existence of record locks (also known as file-segment or  file-
75       region  locks).   The third argument, lock, is a pointer to a structure
76       that has at least the following fields (in unspecified order).
77
78           struct flock {
79               ...
80               short l_type;    /* Type of lock: F_RDLCK,
81                                   F_WRLCK, F_UNLCK */
82               short l_whence;  /* How to interpret l_start:
83                                   SEEK_SET, SEEK_CUR, SEEK_END */
84               off_t l_start;   /* Starting offset for lock */
85               off_t l_len;     /* Number of bytes to lock */
86               pid_t l_pid;     /* PID of process blocking our lock
87                                   (F_GETLK only) */
88               ...
89           };
90
91       The l_whence, l_start, and l_len fields of this structure  specify  the
92       range  of bytes we wish to lock.  Bytes past the end of the file may be
93       locked, but not bytes before the start of the file.
94
95       l_start is the starting offset for the lock, and is  interpreted  rela‐
96       tive  to  either:  the start of the file (if l_whence is SEEK_SET); the
97       current file offset (if l_whence is SEEK_CUR); or the end of  the  file
98       (if  l_whence  is  SEEK_END).  In the final two cases, l_start can be a
99       negative number provided the offset does not lie before  the  start  of
100       the file.
101
102       l_len  specifies  the  number of bytes to be locked.  If l_len is posi‐
103       tive, then the range to be  locked  covers  bytes  l_start  up  to  and
104       including  l_start+l_len-1.   Specifying  0  for  l_len has the special
105       meaning: lock all bytes starting at the location specified by  l_whence
106       and  l_start  through  to the end of file, no matter how large the file
107       grows.
108
109       POSIX.1-2001 allows (but does not require) an implementation to support
110       a negative l_len value; if l_len is negative, the interval described by
111       lock covers bytes l_start+l_len up to and including l_start-1.  This is
112       supported by Linux since kernel versions 2.4.21 and 2.5.49.
113
114       The  l_type  field  can  be  used  to place a read (F_RDLCK) or a write
115       (F_WRLCK) lock on a file.  Any number of processes may hold a read lock
116       (shared  lock)  on a file region, but only one process may hold a write
117       lock (exclusive lock).  An exclusive lock  excludes  all  other  locks,
118       both  shared and exclusive.  A single process can hold only one type of
119       lock on a file region; if a new lock is applied  to  an  already-locked
120       region,  then  the  existing  lock  is  converted to the new lock type.
121       (Such conversions may involve splitting, shrinking, or coalescing  with
122       an  existing  lock if the byte range specified by the new lock does not
123       precisely coincide with the range of the existing lock.)
124
125       F_SETLK (struct flock *)
126              Acquire a lock (when l_type is F_RDLCK or F_WRLCK) or release  a
127              lock  (when  l_type  is  F_UNLCK)  on the bytes specified by the
128              l_whence, l_start, and l_len fields of lock.  If  a  conflicting
129              lock  is  held by another process, this call returns -1 and sets
130              errno to EACCES or EAGAIN.
131
132       F_SETLKW (struct flock *)
133              As for F_SETLK, but if a conflicting lock is held on  the  file,
134              then  wait  for that lock to be released.  If a signal is caught
135              while waiting, then the call is interrupted and (after the  sig‐
136              nal handler has returned) returns immediately (with return value
137              -1 and errno set to EINTR; see signal(7)).
138
139       F_GETLK (struct flock *)
140              On input to this call, lock describes a lock we  would  like  to
141              place  on  the  file.  If the lock could be placed, fcntl() does
142              not actually place it, but returns F_UNLCK in the  l_type  field
143              of  lock and leaves the other fields of the structure unchanged.
144              If one or more incompatible locks would prevent this lock  being
145              placed, then fcntl() returns details about one of these locks in
146              the l_type, l_whence, l_start, and l_len fields of lock and sets
147              l_pid to be the PID of the process holding that lock.
148
149       In  order  to place a read lock, fd must be open for reading.  In order
150       to place a write lock, fd must be open  for  writing.   To  place  both
151       types of lock, open a file read-write.
152
153       As well as being removed by an explicit F_UNLCK, record locks are auto‐
154       matically released when the process terminates or if it closes any file
155       descriptor  referring  to a file on which locks are held.  This is bad:
156       it means that a process can lose the locks on a file  like  /etc/passwd
157       or  /etc/mtab  when for some reason a library function decides to open,
158       read and close it.
159
160       Record locks are not inherited by a child created via fork(2), but  are
161       preserved across an execve(2).
162
163       Because  of the buffering performed by the stdio(3) library, the use of
164       record locking with routines in that package  should  be  avoided;  use
165       read(2) and write(2) instead.
166
167   Mandatory locking
168       (Non-POSIX.)   The  above record locks may be either advisory or manda‐
169       tory, and are advisory by default.
170
171       Advisory locks are not enforced and are useful only between cooperating
172       processes.
173
174       Mandatory  locks are enforced for all processes.  If a process tries to
175       perform an incompatible access (e.g., read(2) or write(2))  on  a  file
176       region that has an incompatible mandatory lock, then the result depends
177       upon whether the O_NONBLOCK flag is enabled for its open file  descrip‐
178       tion.   If  the  O_NONBLOCK  flag  is  not enabled, then system call is
179       blocked until the lock is removed or converted to a mode that  is  com‐
180       patible  with  the access.  If the O_NONBLOCK flag is enabled, then the
181       system call fails with the error EAGAIN .
182
183       To make use of mandatory locks, mandatory locking must be enabled  both
184       on the file system that contains the file to be locked, and on the file
185       itself.  Mandatory locking is enabled on a file system  using  the  "-o
186       mand" option to mount(8), or the MS_MANDLOCK flag for mount(2).  Manda‐
187       tory locking is enabled on a file by disabling group execute permission
188       on  the file and enabling the set-group-ID permission bit (see chmod(1)
189       and chmod(2)).
190
191       The Linux implementation of mandatory locking is unreliable.  See  BUGS
192       below.
193
194   Managing signals
195       F_GETOWN, F_SETOWN, F_GETSIG and F_SETSIG are used to manage I/O avail‐
196       ability signals:
197
198       F_GETOWN (void)
199              Return (as the function result) the process ID or process  group
200              currently  receiving SIGIO and SIGURG signals for events on file
201              descriptor fd.  Process IDs are  returned  as  positive  values;
202              process  group IDs are returned as negative values (but see BUGS
203              below).  arg is ignored.
204
205       F_SETOWN (long)
206              Set the process ID or process group ID that will  receive  SIGIO
207              and  SIGURG  signals  for events on file descriptor fd to the ID
208              given in arg.  A process ID is specified as a positive value;  a
209              process  group  ID  is specified as a negative value.  Most com‐
210              monly, the calling process specifies itself as the  owner  (that
211              is, arg is specified as getpid(2)).
212
213              If you set the O_ASYNC status flag on a file descriptor by using
214              the F_SETFL command of fcntl(), a SIGIO signal is sent  whenever
215              input  or  output  becomes  possible  on  that  file descriptor.
216              F_SETSIG can be used to obtain delivery of a signal  other  than
217              SIGIO.   If  this  permission  check  fails,  then the signal is
218              silently discarded.
219
220              Sending a signal to  the  owner  process  (group)  specified  by
221              F_SETOWN  is  subject  to  the  same  permissions  checks as are
222              described for kill(2), where the sending process is the one that
223              employs F_SETOWN (but see BUGS below).
224
225              If  the  file  descriptor  fd  refers to a socket, F_SETOWN also
226              selects the recipient of SIGURG signals that are delivered  when
227              out-of-band data arrives on that socket.  (SIGURG is sent in any
228              situation where select(2) would report the socket as  having  an
229              "exceptional condition".)
230
231              If  a  non-zero  value  is  given to F_SETSIG in a multithreaded
232              process running with a threading library  that  supports  thread
233              groups (e.g., NPTL), then a positive value given to F_SETOWN has
234              a different meaning: instead of being a process ID identifying a
235              whole  process,  it is a thread ID identifying a specific thread
236              within a process.  Consequently, it may  be  necessary  to  pass
237              F_SETOWN  the  result  of  gettid(2) instead of getpid(2) to get
238              sensible results when  F_SETSIG  is  used.   (In  current  Linux
239              threading implementations, a main thread's thread ID is the same
240              as its process ID.  This means that  a  single-threaded  program
241              can equally use gettid(2) or getpid(2) in this scenario.)  Note,
242              however, that the statements in this paragraph do not  apply  to
243              the  SIGURG  signal  generated for out-of-band data on a socket:
244              this signal is always sent to either  a  process  or  a  process
245              group, depending on the value given to F_SETOWN.  Note also that
246              Linux imposes a limit on the number of  real-time  signals  that
247              may  be queued to a process (see getrlimit(2) and signal(7)) and
248              if this limit is reached, then the kernel reverts to  delivering
249              SIGIO, and this signal is delivered to the entire process rather
250              than to a specific thread.
251
252       F_GETSIG (void)
253              Return (as the function result) the signal sent  when  input  or
254              output  becomes  possible.  A value of zero means SIGIO is sent.
255              Any other value (including SIGIO) is the  signal  sent  instead,
256              and in this case additional info is available to the signal han‐
257              dler if installed with SA_SIGINFO.  arg is ignored.
258
259       F_SETSIG (long)
260              Set the signal sent when input or output becomes possible to the
261              value  given  in arg.  A value of zero means to send the default
262              SIGIO signal.  Any other value (including SIGIO) is  the  signal
263              to  send  instead, and in this case additional info is available
264              to the signal handler if installed with SA_SIGINFO.
265
266              Additionally, passing a non-zero value to F_SETSIG  changes  the
267              signal  recipient  from  a  whole  process  to a specific thread
268              within a process.  See the  description  of  F_SETOWN  for  more
269              details.
270
271              By  using F_SETSIG with a non-zero value, and setting SA_SIGINFO
272              for the signal handler  (see  sigaction(2)),  extra  information
273              about  I/O events is passed to the handler in a siginfo_t struc‐
274              ture.  If the si_code field indicates the  source  is  SI_SIGIO,
275              the  si_fd  field  gives the file descriptor associated with the
276              event.  Otherwise, there is no indication which file descriptors
277              are pending, and you should use the usual mechanisms (select(2),
278              poll(2), read(2) with O_NONBLOCK set etc.)  to  determine  which
279              file descriptors are available for I/O.
280
281              By  selecting  a  real time signal (value >= SIGRTMIN), multiple
282              I/O events may be queued using the same signal numbers.   (Queu‐
283              ing  is  dependent  on  available memory).  Extra information is
284              available if SA_SIGINFO is set for the signal handler, as above.
285
286       Using these mechanisms, a program can implement fully asynchronous  I/O
287       without using select(2) or poll(2) most of the time.
288
289       The  use  of  O_ASYNC, F_GETOWN, F_SETOWN is specific to BSD and Linux.
290       F_GETSIG and F_SETSIG are Linux-specific.  POSIX has  asynchronous  I/O
291       and  the  aio_sigevent  structure  to achieve similar things; these are
292       also available in Linux as part of the GNU C Library (Glibc).
293
294   Leases
295       F_SETLEASE and F_GETLEASE (Linux 2.4 onwards) are  used  (respectively)
296       to  establish  a new lease, and retrieve the current lease, on the open
297       file description referred to by the file descriptor fd.  A  file  lease
298       provides  a mechanism whereby the process holding the lease (the "lease
299       holder") is notified (via delivery of a signal)  when  a  process  (the
300       "lease  breaker")  tries to open(2) or truncate(2) the file referred to
301       by that file descriptor.
302
303       F_SETLEASE (long)
304              Set or remove a file lease according to which of  the  following
305              values is specified in the integer arg:
306
307              F_RDLCK
308                     Take  out  a  read  lease.   This  will cause the calling
309                     process to be notified when the file is opened for  writ‐
310                     ing  or is truncated.  A read lease can only be placed on
311                     a file descriptor that is opened read-only.
312
313              F_WRLCK
314                     Take out a write lease.  This will cause the caller to be
315                     notified  when  the file is opened for reading or writing
316                     or is truncated.  A write lease may be placed on  a  file
317                     only  if there are no other open file descriptors for the
318                     file.
319
320              F_UNLCK
321                     Remove our lease from the file.
322
323       Leases are associated with an  open  file  description  (see  open(2)).
324       This  means  that  duplicate file descriptors (created by, for example,
325       fork(2) or dup(2)) refer to the same lease, and this lease may be modi‐
326       fied  or  released  using  any  of these descriptors.  Furthermore, the
327       lease is released by either an explicit F_UNLCK  operation  on  any  of
328       these  duplicate  descriptors,  or  when all such descriptors have been
329       closed.
330
331       Leases may only be taken out on regular files.  An unprivileged process
332       may  only take out a lease on a file whose UID (owner) matches the file
333       system UID of the process.  A process with the CAP_LEASE capability may
334       take out leases on arbitrary files.
335
336       F_GETLEASE (void)
337              Indicates  what  type  of  lease  is  associated  with  the file
338              descriptor fd by returning either F_RDLCK, F_WRLCK, or  F_UNLCK,
339              indicating,  respectively,  a  read lease , a write lease, or no
340              lease.  arg is ignored.
341
342       When a process (the "lease breaker") performs an open(2) or truncate(2)
343       that conflicts with a lease established via F_SETLEASE, the system call
344       is blocked by the kernel and the kernel notifies the  lease  holder  by
345       sending  it  a  signal  (SIGIO  by  default).   The lease holder should
346       respond to receipt of this signal by doing whatever cleanup is required
347       in  preparation  for  the file to be accessed by another process (e.g.,
348       flushing cached buffers) and then either remove or downgrade its lease.
349       A  lease  is removed by performing an F_SETLEASE command specifying arg
350       as F_UNLCK.  If the lease holder currently holds a write lease  on  the
351       file, and the lease breaker is opening the file for reading, then it is
352       sufficient for the lease holder to downgrade the lease to a read lease.
353       This  is  done  by  performing  an F_SETLEASE command specifying arg as
354       F_RDLCK.
355
356       If the lease holder fails to downgrade or remove the lease  within  the
357       number  of  seconds specified in /proc/sys/fs/lease-break-time then the
358       kernel forcibly removes or downgrades the lease holder's lease.
359
360       Once the lease has been voluntarily or forcibly removed or  downgraded,
361       and  assuming  the lease breaker has not unblocked its system call, the
362       kernel permits the lease breaker's system call to proceed.
363
364       If the lease breaker's blocked open(2) or truncate(2) is interrupted by
365       a  signal handler, then the system call fails with the error EINTR, but
366       the other steps still occur as described above.  If the  lease  breaker
367       is killed by a signal while blocked in open(2) or truncate(2), then the
368       other steps still occur as described above.  If the lease breaker spec‐
369       ifies  the  O_NONBLOCK flag when calling open(2), then the call immedi‐
370       ately fails with the error EWOULDBLOCK, but the other steps still occur
371       as described above.
372
373       The  default  signal used to notify the lease holder is SIGIO, but this
374       can be changed using the F_SETSIG command to fcntl().   If  a  F_SETSIG
375       command  is  performed (even one specifying SIGIO), and the signal han‐
376       dler is established using SA_SIGINFO, then the handler will  receive  a
377       siginfo_t structure as its second argument, and the si_fd field of this
378       argument will hold the descriptor of the  leased  file  that  has  been
379       accessed  by  another  process.   (This  is  useful if the caller holds
380       leases against multiple files).
381
382   File and directory change notification (dnotify)
383       F_NOTIFY (long)
384              (Linux 2.4 onwards)  Provide  notification  when  the  directory
385              referred  to  by  fd  or  any  of  the files that it contains is
386              changed.  The events to be notified are specified in arg,  which
387              is  a  bit  mask specified by ORing together zero or more of the
388              following bits:
389
390              DN_ACCESS   A file was accessed (read, pread, readv)
391              DN_MODIFY   A file was modified (write,  pwrite,  writev,  trun‐
392                          cate, ftruncate).
393              DN_CREATE   A file was created (open, creat, mknod, mkdir, link,
394                          symlink, rename).
395              DN_DELETE   A file  was  unlinked  (unlink,  rename  to  another
396                          directory, rmdir).
397              DN_RENAME   A file was renamed within this directory (rename).
398              DN_ATTRIB   The attributes of a file were changed (chown, chmod,
399                          utime[s]).
400
401              (In order to obtain these definitions, the  _GNU_SOURCE  feature
402              test macro must be defined.)
403
404              Directory  notifications are normally "one-shot", and the appli‐
405              cation  must  re-register  to  receive  further   notifications.
406              Alternatively,  if DN_MULTISHOT is included in arg, then notifi‐
407              cation will remain in effect until explicitly removed.
408
409              A series of F_NOTIFY requests is cumulative, with the events  in
410              arg  being added to the set already monitored.  To disable noti‐
411              fication of all events, make an F_NOTIFY call specifying arg  as
412              0.
413
414              Notification  occurs via delivery of a signal.  The default sig‐
415              nal is SIGIO, but this can be changed using the F_SETSIG command
416              to  fcntl().   In the latter case, the signal handler receives a
417              siginfo_t structure as its second argument (if the  handler  was
418              established using SA_SIGINFO) and the si_fd field of this struc‐
419              ture contains the file descriptor which generated the  notifica‐
420              tion (useful when establishing notification on multiple directo‐
421              ries).
422
423              Especially when using DN_MULTISHOT, a real time signal should be
424              used  for  notification,  so  that multiple notifications can be
425              queued.
426
427              NOTE: New applications should use the inotify interface  (avail‐
428              able since kernel 2.6.13), which provides a much superior inter‐
429              face for obtaining notifications of  file  system  events.   See
430              inotify(7).
431

RETURN VALUE

433       For a successful call, the return value depends on the operation:
434
435       F_DUPFD  The new descriptor.
436
437       F_GETFD  Value of flags.
438
439       F_GETFL  Value of flags.
440
441       F_GETLEASE
442                Type of lease held on file descriptor.
443
444       F_GETOWN Value of descriptor owner.
445
446       F_GETSIG Value  of  signal sent when read or write becomes possible, or
447                zero for traditional SIGIO behavior.
448
449       All other commands
450                Zero.
451
452       On error, -1 is returned, and errno is set appropriately.
453

ERRORS

455       EACCES or EAGAIN
456              Operation is prohibited by locks held by other processes.
457
458       EAGAIN The operation is prohibited because the file  has  been  memory-
459              mapped by another process.
460
461       EBADF  fd is not an open file descriptor, or the command was F_SETLK or
462              F_SETLKW and the file descriptor open mode  doesn't  match  with
463              the type of lock requested.
464
465       EDEADLK
466              It  was detected that the specified F_SETLKW command would cause
467              a deadlock.
468
469       EFAULT lock is outside your accessible address space.
470
471       EINTR  For F_SETLKW, the command was interrupted by a signal; see  sig‐
472              nal(7).  For F_GETLK and F_SETLK, the command was interrupted by
473              a signal before the lock was checked or acquired.   Most  likely
474              when  locking  a  remote  file (e.g., locking over NFS), but can
475              sometimes happen locally.
476
477       EINVAL For F_DUPFD, arg is negative or  is  greater  than  the  maximum
478              allowable  value.   For F_SETSIG, arg is not an allowable signal
479              number.
480
481       EMFILE For F_DUPFD, the process already has the maximum number of  file
482              descriptors open.
483
484       ENOLCK Too  many  segment  locks  open, lock table is full, or a remote
485              locking protocol failed (e.g., locking over NFS).
486
487       EPERM  Attempted to clear the O_APPEND flag on  a  file  that  has  the
488              append-only attribute set.
489

CONFORMING TO

491       SVr4,  4.3BSD,  POSIX.1-2001.   Only  the  operations F_DUPFD, F_GETFD,
492       F_SETFD, F_GETFL, F_SETFL, F_GETLK, F_SETLK,  F_SETLKW,  F_GETOWN,  and
493       F_SETOWN are specified in POSIX.1-2001.
494
495       F_DUPFD_CLOEXEC is specified in POSIX.1-2008.
496
497       F_GETSIG, F_SETSIG, F_NOTIFY, F_GETLEASE, and F_SETLEASE are Linux-spe‐
498       cific.  (Define the _GNU_SOURCE macro to obtain these definitions.)
499

NOTES

501       The errors returned by dup2(2) are different  from  those  returned  by
502       F_DUPFD.
503
504       Since  kernel  2.0,  there  is no interaction between the types of lock
505       placed by flock(2) and fcntl().
506
507       Several systems have more fields in struct flock such as, for  example,
508       l_sysid.   Clearly,  l_pid  alone is not going to be very useful if the
509       process holding the lock may live on a different machine.
510

BUGS

512       A limitation of the Linux system call conventions on some architectures
513       (notably  i386)  means  that  if  a  (negative)  process group ID to be
514       returned by F_GETOWN falls in the range -1 to -4095,  then  the  return
515       value  is  wrongly interpreted by glibc as an error in the system call;
516       that is, the return value of fcntl() will be -1, and errno will contain
517       the (positive) process group ID.
518
519       In  Linux 2.4 and earlier, there is bug that can occur when an unprivi‐
520       leged process uses F_SETOWN to specify  the  owner  of  a  socket  file
521       descriptor  as  a process (group) other than the caller.  In this case,
522       fcntl() can return -1 with errno set to  EPERM,  even  when  the  owner
523       process  (group)  is one that the caller has permission to send signals
524       to.  Despite this error return, the file descriptor owner is  set,  and
525       signals will be sent to the owner.
526
527       The  implementation of mandatory locking in all known versions of Linux
528       is subject to race conditions which render it  unreliable:  a  write(2)
529       call that overlaps with a lock may modify data after the mandatory lock
530       is acquired; a read(2) call  that  overlaps  with  a  lock  may  detect
531       changes  to  data  that were made only after a write lock was acquired.
532       Similar races exist between mandatory locks and mmap(2).  It is  there‐
533       fore inadvisable to rely on mandatory locking.
534

SEE ALSO

536       dup2(2),  flock(2), open(2), socket(2), lockf(3), capabilities(7), fea‐
537       ture_test_macros(7)
538
539       See also locks.txt, mandatory-locking.txt, and dnotify.txt in the  ker‐
540       nel  source  directory  Documentation/filesystems/.  (On older kernels,
541       these files are directly under the Documentation/ directory, and manda‐
542       tory-locking.txt is called mandatory.txt.)
543

COLOPHON

545       This  page  is  part of release 3.22 of the Linux man-pages project.  A
546       description of the project, and information about reporting  bugs,  can
547       be found at http://www.kernel.org/doc/man-pages/.
548
549
550
551Linux                             2009-07-25                          FCNTL(2)
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