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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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CHOWN(3P) POSIX Programmer's Manual CHOWN(3P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
chown, fchownat — change owner and group of a file
#include <unistd.h>
int chown(const char *path, uid_t owner, gid_t group);
#include <fcntl.h>
int fchownat(int fd, const char *path, uid_t owner, gid_t group,
int flag);
The chown() function shall change the user and group ownership of
a file.
The path argument points to a pathname naming a file. The user ID
and group ID of the named file shall be set to the numeric values
contained in owner and group, respectively.
Only processes with an effective user ID equal to the user ID of
the file or with appropriate privileges may change the ownership
of a file. If _POSIX_CHOWN_RESTRICTED is in effect for path:
* Changing the user ID is restricted to processes with
appropriate privileges.
* Changing the group ID is permitted to a process with an
effective user ID equal to the user ID of the file, but
without appropriate privileges, if and only if owner is equal
to the file's user ID or (uid_t)-1 and group is equal either
to the calling process' effective group ID or to one of its
supplementary group IDs.
If the specified file is a regular file, one or more of the
S_IXUSR, S_IXGRP, or S_IXOTH bits of the file mode are set, and
the process does not have appropriate privileges, the set-user-ID
(S_ISUID) and set-group-ID (S_ISGID) bits of the file mode shall
be cleared upon successful return from chown(). If the specified
file is a regular file, one or more of the S_IXUSR, S_IXGRP, or
S_IXOTH bits of the file mode are set, and the process has
appropriate privileges, it is implementation-defined whether the
set-user-ID and set-group-ID bits are altered. If the chown()
function is successfully invoked on a file that is not a regular
file and one or more of the S_IXUSR, S_IXGRP, or S_IXOTH bits of
the file mode are set, the set-user-ID and set-group-ID bits may
be cleared.
If owner or group is specified as (uid_t)-1 or (gid_t)-1,
respectively, the corresponding ID of the file shall not be
changed.
Upon successful completion, chown() shall mark for update the
last file status change timestamp of the file, except that if
owner is (uid_t)-1 and group is (gid_t)-1, the file status change
timestamp need not be marked for update.
The fchownat() function shall be equivalent to the chown() and
lchown() functions 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. If the access mode of
the open file description associated with the file descriptor is
not O_SEARCH, the function shall check whether directory searches
are permitted using the current permissions of the directory
underlying the file descriptor. If the access mode is O_SEARCH,
the function shall not perform the check.
Values for flag are constructed by a bitwise-inclusive OR of
flags from the following list, defined in <fcntl.h>:
AT_SYMLINK_NOFOLLOW
If path names a symbolic link, ownership of the symbolic
link is changed.
If fchownat() is passed the special value AT_FDCWD in the fd
parameter, the current working directory shall be used and the
behavior shall be identical to a call to chown() or lchown()
respectively, depending on whether or not the AT_SYMLINK_NOFOLLOW
bit is set in the flag argument.
Upon successful completion, these functions shall return 0.
Otherwise, these functions shall return -1 and set errno to
indicate the error. If -1 is returned, no changes are made in the
user ID and group ID of the file.
These functions shall fail if:
EACCES Search permission is denied on a component of the path
prefix.
ELOOP A loop exists in symbolic links encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of path does not name an existing file or path
is an empty string.
ENOTDIR
A component of the path prefix names an existing file that
is neither a directory nor a symbolic link to a directory,
or the path argument contains at least one non-<slash>
character and ends with one or more trailing <slash>
characters and the last pathname component names an
existing file that is neither a directory nor a symbolic
link to a directory.
EPERM The effective user ID does not match the owner of the
file, or the calling process does not have appropriate
privileges and _POSIX_CHOWN_RESTRICTED indicates that such
privilege is required.
EROFS The named file resides on a read-only file system.
The fchownat() function shall fail if:
EACCES The access mode of the open file description associated
with fd is not O_SEARCH and the permissions of the
directory underlying fd do not permit directory searches.
EBADF The path argument does not specify an absolute path and
the fd argument is neither AT_FDCWD nor a valid file
descriptor open for reading or searching.
ENOTDIR
The path argument is not an absolute path and fd is a file
descriptor associated with a non-directory file.
These functions may fail if:
EIO An I/O error occurred while reading or writing to the file
system.
EINTR The chown() function was interrupted by a signal which was
caught.
EINVAL The owner or group ID supplied is not a value supported by
the implementation.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
The fchownat() function may fail if:
EINVAL The value of the flag argument is not valid.
The following sections are informative.
None.
Although chown() can be used on some implementations by the file
owner to change the owner and group to any desired values, the
only portable use of this function is to change the group of a
file to the effective GID of the calling process or to a member
of its group set.
System III and System V allow a user to give away files; that is,
the owner of a file may change its user ID to anything. This is a
serious problem for implementations that are intended to meet
government security regulations. Version 7 and 4.3 BSD permit
only the superuser to change the user ID of a file. Some
government agencies (usually not ones concerned directly with
security) find this limitation too confining. This volume of
POSIX.1‐2017 uses may to permit secure implementations while not
disallowing System V.
System III and System V allow the owner of a file to change the
group ID to anything. Version 7 permits only the superuser to
change the group ID of a file. 4.3 BSD permits the owner to
change the group ID of a file to its effective group ID or to any
of the groups in the list of supplementary group IDs, but to no
others.
The POSIX.1‐1990 standard requires that the chown() function
invoked by a non-appropriate privileged process clear the S_ISGID
and the S_ISUID bits for regular files, and permits them to be
cleared for other types of files. This is so that changes in
accessibility do not accidentally cause files to become security
holes. Unfortunately, requiring these bits to be cleared on non-
executable data files also clears the mandatory file locking bit
(shared with S_ISGID), which is an extension on many
implementations (it first appeared in System V). These bits
should only be required to be cleared on regular files that have
one or more of their execute bits set.
The purpose of the fchownat() function is to enable changing
ownership of files in directories other than the current working
directory without exposure to race conditions. Any part of the
path of a file could be changed in parallel to a call to chown()
or lchown(), resulting in unspecified behavior. By opening a file
descriptor for the target directory and using the fchownat()
function it can be guaranteed that the changed file is located
relative to the desired directory.
None.
chmod(3p), fpathconf(3p), lchown(3p)
The Base Definitions volume of POSIX.1‐2017, fcntl.h(0p),
sys_types.h(0p), unistd.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any
discrepancy between this version and the original IEEE and The
Open Group Standard, the original IEEE and The Open Group
Standard is the referee document. The original Standard can be
obtained online at http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 CHOWN(3P)
Pages that refer to this page: unistd.h(0p), chgrp(1p), chown(1p), pax(1p), chmod(3p), fchmod(3p), fchown(3p), fchownat(3p), fpathconf(3p), fstatvfs(3p), lchown(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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