public Class FCNTL

Enum values:

• DN_ACCESS - A file was accessed (read(2), pread(2), readv(2), and similar).
• DN_MODIFY - A file was modified (write(2), pwrite(2), writev(2), truncate(2), ftruncate(2), and similar).
• DN_CREATE - A file was created (open(2), creat(2), mknod(2), mkdir(2), link(2), symlink(2), rename(2) into this directory).
• DN_DELETE - A file was unlinked (unlink(2), rename(2) to another directory, rmdir(2)).
• DN_RENAME - A file was renamed within this directory (rename(2)).
• DN_ATTRIB - The attributes of a file were changed (chown(2), chmod(2), utime(2), utimensat(2), and similar).
• DN_MULTISHOT - Don't remove notifier

Enum values:

• DN_ACCESS - A file was accessed (read(2), pread(2), readv(2), and similar).
• DN_MODIFY - A file was modified (write(2), pwrite(2), writev(2), truncate(2), ftruncate(2), and similar).
• DN_CREATE - A file was created (open(2), creat(2), mknod(2), mkdir(2), link(2), symlink(2), rename(2) into this directory).
• DN_DELETE - A file was unlinked (unlink(2), rename(2) to another directory, rmdir(2)).
• DN_RENAME - A file was renamed within this directory (rename(2)).
• DN_ATTRIB - The attributes of a file were changed (chown(2), chmod(2), utime(2), utimensat(2), and similar).
• DN_MULTISHOT - Don't remove notifier

Enum values:

• DN_ACCESS - A file was accessed (read(2), pread(2), readv(2), and similar).
• DN_MODIFY - A file was modified (write(2), pwrite(2), writev(2), truncate(2), ftruncate(2), and similar).
• DN_CREATE - A file was created (open(2), creat(2), mknod(2), mkdir(2), link(2), symlink(2), rename(2) into this directory).
• DN_DELETE - A file was unlinked (unlink(2), rename(2) to another directory, rmdir(2)).
• DN_RENAME - A file was renamed within this directory (rename(2)).
• DN_ATTRIB - The attributes of a file were changed (chown(2), chmod(2), utime(2), utimensat(2), and similar).
• DN_MULTISHOT - Don't remove notifier

Enum values:

• DN_ACCESS - A file was accessed (read(2), pread(2), readv(2), and similar).
• DN_MODIFY - A file was modified (write(2), pwrite(2), writev(2), truncate(2), ftruncate(2), and similar).
• DN_CREATE - A file was created (open(2), creat(2), mknod(2), mkdir(2), link(2), symlink(2), rename(2) into this directory).
• DN_DELETE - A file was unlinked (unlink(2), rename(2) to another directory, rmdir(2)).
• DN_RENAME - A file was renamed within this directory (rename(2)).
• DN_ATTRIB - The attributes of a file were changed (chown(2), chmod(2), utime(2), utimensat(2), and similar).
• DN_MULTISHOT - Don't remove notifier

fcntl commands.

For posix fcntl and l_type field of an Flock for lockf().

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

FOwnerEx::type values.

FOwnerEx::type values.

Enum values:

• F_SEAL_SEAL - If this seal is set, any further call to fcntl() with F_ADD_SEALS fails with the error EPERM.

  Therefore, this seal prevents any modifications to the set of seals itself. If the initial set of seals of a file includes F_SEAL_SEAL, then this effectively causes the set of seals to be constant and locked.

• F_SEAL_SHRINK - If this seal is set, the file in question cannot be reduced in size.

  This affects open(2) with the O_TRUNC flag as well as truncate(2) and ftruncate(2). Those calls fail with EPERM if you try to shrink the file in question. Increasing the file size is still possible.

• F_SEAL_GROW - If this seal is set, the size of the file in question cannot be increased.

  This affects write(2) beyond the end of the file, truncate(2), ftruncate(2), and fallocate(2). These calls fail with EPERM if you use them to increase the file size. If you keep the size or shrink it, those calls still work as expected.

• F_SEAL_WRITE - If this seal is set, you cannot modify the contents of the file.

  Note that shrinking or growing the size of the file is still possible and allowed. Thus, this seal is normally used in combination with one of the other seals. This seal affects write(2) and fallocate(2) (only in combination with the FALLOC_FL_PUNCH_HOLE flag). Those calls fail with EPERM if this seal is set. Furthermore, trying to create new shared, writable memory-mappings via mmap(2) will also fail with EPERM.

  Using the F_ADD_SEALS operation to set the F_SEAL_WRITE seal fails with EBUSY if any writable, shared mapping exists. Such mappings must be unmapped before you can add this seal. Furthermore, if there are any asynchronous I/O operations (io_submit(2)) pending on the file, all outstanding writes will be discarded.

• F_SEAL_FUTURE_WRITE - The effect of this seal is similar to F_SEAL_WRITE, but the contents of the file can still be modified via shared writable mappings that were created prior to the seal being set.

  Any attempt to create a new writable mapping on the file via mmap(2) will fail with EPERM. Likewise, an attempt to write to the file via write(2) will fail with EPERM.

  Using this seal, one process can create a memory buffer that it can continue to modify while sharing that buffer on a "read-only" basis with other processes.

  (since Linux 5.1)

Enum values:

• F_SEAL_SEAL - If this seal is set, any further call to fcntl() with F_ADD_SEALS fails with the error EPERM.

  Therefore, this seal prevents any modifications to the set of seals itself. If the initial set of seals of a file includes F_SEAL_SEAL, then this effectively causes the set of seals to be constant and locked.

• F_SEAL_SHRINK - If this seal is set, the file in question cannot be reduced in size.

  This affects open(2) with the O_TRUNC flag as well as truncate(2) and ftruncate(2). Those calls fail with EPERM if you try to shrink the file in question. Increasing the file size is still possible.

• F_SEAL_GROW - If this seal is set, the size of the file in question cannot be increased.

  This affects write(2) beyond the end of the file, truncate(2), ftruncate(2), and fallocate(2). These calls fail with EPERM if you use them to increase the file size. If you keep the size or shrink it, those calls still work as expected.

• F_SEAL_WRITE - If this seal is set, you cannot modify the contents of the file.

  Note that shrinking or growing the size of the file is still possible and allowed. Thus, this seal is normally used in combination with one of the other seals. This seal affects write(2) and fallocate(2) (only in combination with the FALLOC_FL_PUNCH_HOLE flag). Those calls fail with EPERM if this seal is set. Furthermore, trying to create new shared, writable memory-mappings via mmap(2) will also fail with EPERM.

  Using the F_ADD_SEALS operation to set the F_SEAL_WRITE seal fails with EBUSY if any writable, shared mapping exists. Such mappings must be unmapped before you can add this seal. Furthermore, if there are any asynchronous I/O operations (io_submit(2)) pending on the file, all outstanding writes will be discarded.

• F_SEAL_FUTURE_WRITE - The effect of this seal is similar to F_SEAL_WRITE, but the contents of the file can still be modified via shared writable mappings that were created prior to the seal being set.

  Any attempt to create a new writable mapping on the file via mmap(2) will fail with EPERM. Likewise, an attempt to write to the file via write(2) will fail with EPERM.

  Using this seal, one process can create a memory buffer that it can continue to modify while sharing that buffer on a "read-only" basis with other processes.

  (since Linux 5.1)

Enum values:

• F_SEAL_SEAL - If this seal is set, any further call to fcntl() with F_ADD_SEALS fails with the error EPERM.

  Therefore, this seal prevents any modifications to the set of seals itself. If the initial set of seals of a file includes F_SEAL_SEAL, then this effectively causes the set of seals to be constant and locked.

• F_SEAL_SHRINK - If this seal is set, the file in question cannot be reduced in size.

  This affects open(2) with the O_TRUNC flag as well as truncate(2) and ftruncate(2). Those calls fail with EPERM if you try to shrink the file in question. Increasing the file size is still possible.

• F_SEAL_GROW - If this seal is set, the size of the file in question cannot be increased.

  This affects write(2) beyond the end of the file, truncate(2), ftruncate(2), and fallocate(2). These calls fail with EPERM if you use them to increase the file size. If you keep the size or shrink it, those calls still work as expected.

• F_SEAL_WRITE - If this seal is set, you cannot modify the contents of the file.

  Note that shrinking or growing the size of the file is still possible and allowed. Thus, this seal is normally used in combination with one of the other seals. This seal affects write(2) and fallocate(2) (only in combination with the FALLOC_FL_PUNCH_HOLE flag). Those calls fail with EPERM if this seal is set. Furthermore, trying to create new shared, writable memory-mappings via mmap(2) will also fail with EPERM.

  Using the F_ADD_SEALS operation to set the F_SEAL_WRITE seal fails with EBUSY if any writable, shared mapping exists. Such mappings must be unmapped before you can add this seal. Furthermore, if there are any asynchronous I/O operations (io_submit(2)) pending on the file, all outstanding writes will be discarded.

• F_SEAL_FUTURE_WRITE - The effect of this seal is similar to F_SEAL_WRITE, but the contents of the file can still be modified via shared writable mappings that were created prior to the seal being set.

  Any attempt to create a new writable mapping on the file via mmap(2) will fail with EPERM. Likewise, an attempt to write to the file via write(2) will fail with EPERM.

  Using this seal, one process can create a memory buffer that it can continue to modify while sharing that buffer on a "read-only" basis with other processes.

  (since Linux 5.1)

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

fcntl commands.

For posix fcntl and l_type field of an Flock for lockf().

For posix fcntl and l_type field of an Flock for lockf().

Enum values:

• LOCK_SH - shared lock
• LOCK_EX - exclusive lock
• LOCK_NB - or'd with one of the above to prevent blocking
• LOCK_UN - remove lock
• LOCK_MAND - This is a mandatory flock...
• LOCK_READ - which allows concurrent read operations
• LOCK_WRITE - which allows concurrent write operations
• LOCK_RW - which allows concurrent read & writes ops

Enum values:

• LOCK_SH - shared lock
• LOCK_EX - exclusive lock
• LOCK_NB - or'd with one of the above to prevent blocking
• LOCK_UN - remove lock
• LOCK_MAND - This is a mandatory flock...
• LOCK_READ - which allows concurrent read operations
• LOCK_WRITE - which allows concurrent write operations
• LOCK_RW - which allows concurrent read & writes ops

Enum values:

• LOCK_SH - shared lock
• LOCK_EX - exclusive lock
• LOCK_NB - or'd with one of the above to prevent blocking
• LOCK_UN - remove lock
• LOCK_MAND - This is a mandatory flock...
• LOCK_READ - which allows concurrent read operations
• LOCK_WRITE - which allows concurrent write operations
• LOCK_RW - which allows concurrent read & writes ops

Enum values:

• LOCK_SH - shared lock
• LOCK_EX - exclusive lock
• LOCK_NB - or'd with one of the above to prevent blocking
• LOCK_UN - remove lock
• LOCK_MAND - This is a mandatory flock...
• LOCK_READ - which allows concurrent read operations
• LOCK_WRITE - which allows concurrent write operations
• LOCK_RW - which allows concurrent read & writes ops

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• O_ACCMODE
• O_RDONLY
• O_WRONLY
• O_RDWR
• O_APPEND - The file is opened in append mode.

  Before each write(2), the file offset is positioned at the end of the file, as if with lseek(2). O_APPEND may lead to corrupted files on NFS file systems if more than one process appends data to a file at once. This is because NFS does not support appending to a file, so the client kernel has to simulate it, which can't be done without a race condition.

• O_ASYNC - Enable signal-driven I/O: generate a signal (SIGIO by default, but this can be changed via fcntl(2)) when input or output becomes possible on this file descriptor.

  This feature is only available for terminals, pseudoterminals, sockets, and (since Linux 2.6) pipes and FIFOs. See fcntl(2) for further details.

• O_CLOEXEC - Enable the close-on-exec flag for the new file descriptor.

  Specifying this flag permits a program to avoid additional fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag. Additionally, use of this flag is essential in some multithreaded programs since using a separate fcntl(2) F_SETFD operation to set the FD_CLOEXEC flag does not suffice to avoid race conditions where one thread opens a file descriptor at the same time as another thread does a fork(2) plus execve(2).

• O_CREAT - If the file does not exist it will be created.

  The owner (user ID) of the file is set to the effective user ID of the process. The group ownership (group ID) is set either to the effective group ID of the process or to the group ID of the parent directory (depending on file system type and mount options, and the mode of the parent directory, see the mount options bsdgroups and sysvgroups described in mount(8)).

• O_DIRECT - Try to minimize cache effects of the I/O to and from this file.

  In general this will degrade performance, but it is useful in special situations, such as when applications do their own caching. File I/O is done directly to/from user-space buffers. The O_DIRECT flag on its own makes an effort to transfer data synchronously, but does not give the guarantees of the O_SYNC flag that data and necessary metadata are transferred. To guarantee synchronous I/O, O_SYNC must be used in addition to O_DIRECT.

  A semantically similar (but deprecated) interface for block devices is described in raw(8).

• O_DIRECTORY - If pathname is not a directory, cause the open to fail.

  This flag is Linux-specific, and was added in kernel version 2.1.126, to avoid denial-of-service problems if opendir(3) is called on a FIFO or tape device, but should not be used outside of the implementation of opendir(3).

• O_DSYNC
• O_EXCL - Ensure that this call creates the file: if this flag is specified in conjunction with O_CREAT, and pathname already exists, then open() will fail.

  When these two flags are specified, symbolic links are not followed: if pathname is a symbolic link, then open() fails regardless of where the symbolic link points to.

  In general, the behavior of O_EXCL is undefined if it is used without O_CREAT. There is one exception: on Linux 2.6 and later, O_EXCL can be used without O_CREAT if pathname refers to a block device. If the block device is in use by the system (e.g., mounted), open() fails with the error EBUSY.

  On NFS, O_EXCL is only supported when using NFSv3 or later on kernel 2.6 or later. In NFS environments where O_EXCL support is not provided, programs that rely on it for performing locking tasks will contain a race condition. Portable programs that want to perform atomic file locking using a lockfile, and need to avoid reliance on NFS support for O_EXCL, can create a unique file on the same file system (e.g., incorporating hostname and PID), and use link(2) to make a link to the lockfile. If link(2) returns 0, the lock is successful. Otherwise, use stat(2) on the unique file to check if its link count has increased to 2, in which case the lock is also successful.

• O_LARGEFILE - (LFS) Allow files whose sizes cannot be represented in an off_t (but can be represented in an off64_t) to be opened.

  The _LARGEFILE64_SOURCE macro must be defined (before including any header files) in order to obtain this definition. Setting the _FILE_OFFSET_BITS feature test macro to 64 (rather than using O_LARGEFILE) is the preferred method of accessing large files on 32-bit systems (see feature_test_macros(7)).

• O_NOATIME - Do not update the file last access time (st_atime in the inode) when the file is read(2).

  This flag is intended for use by indexing or backup programs, where its use can significantly reduce the amount of disk activity. This flag may not be effective on all file systems. One example is NFS, where the server maintains the access time.

• O_NOCTTY - If pathname refers to a terminal device --see tty(4)-- it will not become the process's controlling terminal even if the process does not have one.
• O_NOFOLLOW - If pathname is a symbolic link, then the open fails.

  This is a FreeBSD extension, which was added to Linux in version 2.1.126. Symbolic links in earlier components of the pathname will still be followed.

• O_NONBLOCK - When possible, the file is opened in nonblocking mode.

  Neither the open() nor any subsequent operations on the file descriptor which is returned will cause the calling process to wait. For the handling of FIFOs (named pipes), see also fifo(7). For a discussion of the effect of O_NONBLOCK in conjunction with mandatory file locks and with file leases, see fcntl(2).

• O_NDELAY
• O_PATH
• O_SYNC - The file is opened for synchronous I/O.

  Any write(2)s on the resulting file descriptor will block the calling process until the data has been physically written to the underlying hardware.

• O_TMPFILE
• O_TRUNC - If the file already exists and is a regular file and the open mode allows writing (i.e., is O_RDWR or O_WRONLY) it will be truncated to length 0.

  If the file is a FIFO or terminal device file, the O_TRUNC flag is ignored. Otherwise the effect of O_TRUNC is unspecified.

Enum values:

• RWH_WRITE_LIFE_NOT_SET - No specific hint has been set. This is the default value.
• RWH_WRITE_LIFE_NONE - No specific write lifetime is associated with this file or inode.
• RWH_WRITE_LIFE_SHORT - Data written to this inode or via this open file description is expected to have a short lifetime.
• RWH_WRITE_LIFE_MEDIUM - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_SHORT.
• RWH_WRITE_LIFE_LONG - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_MEDIUM.
• RWH_WRITE_LIFE_EXTREME - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_LONG.

Enum values:

• RWH_WRITE_LIFE_NOT_SET - No specific hint has been set. This is the default value.
• RWH_WRITE_LIFE_NONE - No specific write lifetime is associated with this file or inode.
• RWH_WRITE_LIFE_SHORT - Data written to this inode or via this open file description is expected to have a short lifetime.
• RWH_WRITE_LIFE_MEDIUM - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_SHORT.
• RWH_WRITE_LIFE_LONG - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_MEDIUM.
• RWH_WRITE_LIFE_EXTREME - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_LONG.

Enum values:

• RWH_WRITE_LIFE_NOT_SET - No specific hint has been set. This is the default value.
• RWH_WRITE_LIFE_NONE - No specific write lifetime is associated with this file or inode.
• RWH_WRITE_LIFE_SHORT - Data written to this inode or via this open file description is expected to have a short lifetime.
• RWH_WRITE_LIFE_MEDIUM - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_SHORT.
• RWH_WRITE_LIFE_LONG - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_MEDIUM.
• RWH_WRITE_LIFE_EXTREME - Data written to this inode or via this open file description is expected to have a lifetime longer than data written with RWH_WRITE_LIFE_LONG.

File types encoded in type mode_t.

File types encoded in type mode_t.

File types encoded in type mode_t.

File types encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.

File mode bits encoded in type mode_t.