freebsd-src/lib/libsys/chown.2

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.Dd March 30, 2021
.Dt CHOWN 2
.Os
.Sh NAME
.Nm chown ,
.Nm fchown ,
.Nm lchown ,
.Nm fchownat
.Nd change owner and group of a file
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn chown "const char *path" "uid_t owner" "gid_t group"
.Ft int
.Fn fchown "int fd" "uid_t owner" "gid_t group"
.Ft int
.Fn lchown "const char *path" "uid_t owner" "gid_t group"
.Ft int
.Fn fchownat "int fd" "const char *path" "uid_t owner" "gid_t group" "int flag"
.Sh DESCRIPTION
The owner ID and group ID of the file
named by
.Fa path
or referenced by
.Fa fd
is changed as specified by the arguments
.Fa owner
and
.Fa group .
The owner of a file may change the
.Fa group
to a group of which
he or she is a member,
but the change
.Fa owner
capability is restricted to the super-user.
.Pp
The
.Fn chown
system call
clears the set-user-id and set-group-id bits
on the file
to prevent accidental or mischievous creation of
set-user-id and set-group-id programs if not executed
by the super-user.
The
.Fn chown
system call
follows symbolic links to operate on the target of the link
rather than the link itself.
.Pp
The
.Fn fchown
system call
is particularly useful when used in conjunction
with the file locking primitives (see
.Xr flock 2 ) .
.Pp
The
.Fn lchown
system call is similar to
.Fn chown
but does not follow symbolic links.
.Pp
The
.Fn fchownat
system call is equivalent to the
.Fn chown
and
.Fn lchown
except in the case where
.Fa path
specifies a relative path.
In this case the file to be changed is determined relative to the directory
associated with the file descriptor
.Fa fd
instead of the current working directory.
.Pp
Values for
.Fa flag
are constructed by a bitwise-inclusive OR of flags from the following
list, defined in
.In fcntl.h :
.Bl -tag -width indent
.It Dv AT_SYMLINK_NOFOLLOW
If
.Fa path
names a symbolic link, ownership of the symbolic link is changed.
.It Dv AT_RESOLVE_BENEATH
Only walk paths below the directory specified by the
.Ar fd
descriptor.
See the description of the
.Dv O_RESOLVE_BENEATH
flag in the
.Xr open 2
manual page.
.It Dv AT_EMPTY_PATH
If the
.Fa path
argument is an empty string, operate on the file or directory
referenced by the descriptor
.Fa fd .
If
.Fa fd
is equal to
.Dv AT_FDCWD ,
operate on the current working directory.
.El
.Pp
If
.Fn fchownat
is passed the special value
.Dv AT_FDCWD
in the
.Fa fd
parameter, the current working directory is used and the behavior is identical
to a call to
.Fn chown
or
.Fn lchown
respectively, depending on whether or not the
.Dv AT_SYMLINK_NOFOLLOW
bit is set in the
.Fa flag
argument.
.Pp
One of the owner or group id's
may be left unchanged by specifying it as -1.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
The
.Fn chown
and
.Fn lchown
will fail and the file will be unchanged if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded 255 characters,
or an entire path name exceeded 1023 characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EPERM
The operation would change the ownership, but the effective user ID is not the
super-user.
.It Bq Er EPERM
The named file has its immutable or append-only flag set, see the
.Xr chflags 2
manual page for more information.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er EFAULT
The
.Fa path
argument
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er EINTEGRITY
Corrupted data was detected while reading from the file system.
.El
.Pp
The
.Fn fchown
system call will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
does not refer to a valid descriptor.
.It Bq Er EINVAL
The
.Fa fd
argument
refers to a socket, not a file.
.It Bq Er EPERM
The effective user ID is not the super-user.
.It Bq Er EROFS
The named file resides on a read-only file system.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er EINTEGRITY
Corrupted data was detected while reading from the file system.
.El
.Pp
In addition to the errors specified for
.Fn chown
and
.Fn lchown ,
the
.Fn fchownat
system call may fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa path
argument does not specify an absolute path and the
.Fa fd
argument is neither
.Dv AT_FDCWD
nor a valid file descriptor open for searching.
.It Bq Er EINVAL
The value of the
.Fa flag
argument is not valid.
.It Bq Er ENOTDIR
The
.Fa path
argument is not an absolute path and
.Fa fd
is neither
.Dv AT_FDCWD
nor a file descriptor associated with a directory.
.It Bq Er ENOTCAPABLE
.Fa path
is an absolute path,
or contained a ".." component leading to a
directory outside of the directory hierarchy specified by
.Fa fd ,
and the process is in capability mode or the
.Dv AT_RESOLVE_BENEATH
flag was specified.
.El
.Sh SEE ALSO
.Xr chgrp 1 ,
.Xr chflags 2 ,
.Xr chmod 2 ,
.Xr flock 2 ,
.Xr chown 8
.Sh STANDARDS
The
.Fn chown
system call is expected to conform to
.St -p1003.1-90 .
The
.Fn fchownat
system call follows The Open Group Extended API Set 2 specification.
.Sh HISTORY
The
.Fn chown
function appeared in
.At v1 .
The
.Fn fchown
system call appeared in
.Bx 4.2 .
.Pp
The
.Fn chown
system call was changed to follow symbolic links in
.Bx 4.4 .
The
.Fn lchown
system call was added in
.Fx 3.0
to compensate for the loss of functionality.
.Pp
The
.Fn fchownat
system call appeared in
.Fx 8.0 .