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CHFLAGS(2) System Calls Manual CHFLAGS(2)

chflags, lchflags, fchflags, chflagsat — set file flags

library “libc”

#include <sys/stat.h>
#include <unistd.h>

int
chflags(const char *path, unsigned long flags);

int
lchflags(const char *path, unsigned long flags);

int
fchflags(int fd, unsigned long flags);

int
chflagsat(int fd, const char *path, unsigned long flags, int atflag);

The file whose name is given by path or referenced by the descriptor fd has its flags changed to flags.

The () system call is like () except in the case where the named file is a symbolic link, in which case lchflags() will change the flags of the link itself, rather than the file it points to.

The () is equivalent to either () or lchflags() depending on the atflag except in the case where path specifies a relative path. In this case the file to be changed is determined relative to the directory associated with the file descriptor fd instead of the current working directory. The values for the atflag are constructed by a bitwise-inclusive OR of flags from the following list, defined in <fcntl.h>:

If path names a symbolic link, then the flags of the symbolic link are changed.

If () is passed the special value AT_FDCWD in the fd parameter, the current working directory is used. If also atflag is zero, the behavior is identical to a call to ().

The flags specified are formed by 'ing the following values

The file may only be appended to.
The file has been archived. This flag means the opposite of the DOS, Windows and CIFS FILE_ATTRIBUTE_ARCHIVE attribute. This flag has been deprecated, and may be removed in a future release.
The file may not be changed.
The file may not be renamed or deleted.
The file is a snapshot file.
The file may only be appended to.
The file needs to be archived. This flag has the same meaning as the DOS, Windows and CIFS FILE_ATTRIBUTE_ARCHIVE attribute. Filesystems in FreeBSD may or may not have special handling for this flag. For instance, ZFS tracks changes to files and will set this bit when a file is updated. UFS only stores the flag, and relies on the application to change it when needed.
The file may be hidden from directory listings at the application's discretion. The file has the DOS, Windows and CIFS FILE_ATTRIBUTE_HIDDEN attribute.
The file may not be changed.
Do not dump the file.
The file may not be renamed or deleted.
The file is offline, or has the Windows and CIFS FILE_ATTRIBUTE_OFFLINE attribute. Filesystems in FreeBSD store and display this flag, but do not provide any special handling when it is set.
The directory is opaque when viewed through a union stack.
The file is read only, and may not be written or appended. Filesystems may use this flag to maintain compatibility with the DOS, Windows and CIFS FILE_ATTRIBUTE_READONLY attribute.
The file contains a Windows reparse point and has the Windows and CIFS FILE_ATTRIBUTE_REPARSE_POINT attribute.
The file has the Windows FILE_ATTRIBUTE_SPARSE_FILE attribute. This may also be used by a filesystem to indicate a sparse file.
The file has the DOS, Windows and CIFS FILE_ATTRIBUTE_SYSTEM attribute. Filesystems in FreeBSD may store and display this flag, but do not provide any special handling when it is set.

If one of SF_IMMUTABLE, SF_APPEND, or SF_NOUNLINK is set a non-super-user cannot change any flags and even the super-user can change flags only if securelevel is 0. (See init(8) for details.)

The UF_IMMUTABLE, UF_APPEND, UF_NOUNLINK, UF_NODUMP, and UF_OPAQUE flags may be set or unset by either the owner of a file or the super-user.

The SF_IMMUTABLE, SF_APPEND, SF_NOUNLINK, and SF_ARCHIVED flags may only be set or unset by the super-user. Attempts to toggle these flags by non-super-users are rejected. These flags may be set at any time, but normally may only be unset when the system is in single-user mode. (See init(8) for details.)

The implementation of all flags is filesystem-dependent. See the description of the UF_ARCHIVE flag above for one example of the differences in behavior. Care should be exercised when writing applications to account for support or lack of support of these flags in various filesystems.

The SF_SNAPSHOT flag is maintained by the system and cannot be toggled.

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The chflags() system call will fail if:

[]
A component of the path prefix is not a directory.
[]
A component of a pathname exceeded 255 characters, or an entire path name exceeded 1023 characters.
[]
The named file does not exist.
[]
Search permission is denied for a component of the path prefix.
[]
Too many symbolic links were encountered in translating the pathname.
[]
The effective user ID does not match the owner of the file and the effective user ID is not the super-user.
[]
One of SF_IMMUTABLE, SF_APPEND, or SF_NOUNLINK is set and the user is either not the super-user or securelevel is greater than 0.
[]
A non-super-user attempted to toggle one of SF_ARCHIVED, SF_IMMUTABLE, SF_APPEND, or SF_NOUNLINK.
[]
An attempt was made to toggle the SF_SNAPSHOT flag.
[]
The named file resides on a read-only file system.
[]
The path argument points outside the process's allocated address space.
[]
An I/O error occurred while reading from or writing to the file system.
[]
The underlying file system does not support file flags, or does not support all of the flags set in flags.

The fchflags() system call will fail if:

[]
The descriptor is not valid.
[]
The fd argument refers to a socket, not to a file.
[]
The effective user ID does not match the owner of the file and the effective user ID is not the super-user.
[]
One of SF_IMMUTABLE, SF_APPEND, or SF_NOUNLINK is set and the user is either not the super-user or securelevel is greater than 0.
[]
A non-super-user attempted to toggle one of SF_ARCHIVED, SF_IMMUTABLE, SF_APPEND, or SF_NOUNLINK.
[]
An attempt was made to toggle the SF_SNAPSHOT flag.
[]
The file resides on a read-only file system.
[]
An I/O error occurred while reading from or writing to the file system.
[]
The underlying file system does not support file flags, or does not support all of the flags set in flags.

chflags(1), fflagstostr(3), strtofflags(3), init(8), mount_unionfs(8)

The chflags() and fchflags() system calls first appeared in 4.4BSD. The lchflags() system call first appeared in FreeBSD 5.0. The chflagsat() system call first appeared in FreeBSD 10.0.

March 22, 2013 FreeBSD-12.0