chown(2) - Linux manual page (original) (raw)
chown(2) System Calls Manual chown(2)
NAME top
chown, fchown, lchown, fchownat - change ownership of a fileLIBRARY top
Standard C library (_libc_, _-lc_)SYNOPSIS top
**#include <unistd.h>**
**int chown(const char ***_pathname_**, uid_t** _owner_**, gid_t** _group_**);**
**int fchown(int** _fd_**, uid_t** _owner_**, gid_t** _group_**);**
**int lchown(const char ***_pathname_**, uid_t** _owner_**, gid_t** _group_**);**
**#include <fcntl.h>** /* Definition of AT_* constants */
**#include <unistd.h>**
**int fchownat(int** _dirfd_**, const char ***_pathname_**,**
**uid_t** _owner_**, gid_t** _group_**, int** _flags_**);**Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
**fchown**(), **lchown**():
/* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
|| _XOPEN_SOURCE >= 500
|| /* glibc <= 2.19: */ _BSD_SOURCE
**fchownat**():
Since glibc 2.10:
_POSIX_C_SOURCE >= 200809L
Before glibc 2.10:
_ATFILE_SOURCEDESCRIPTION top
These system calls change the owner and group of a file. The
**chown**(), **fchown**(), and **lchown**() system calls differ only in how
the file is specified:
• **chown**() changes the ownership of the file specified by
_pathname_, which is dereferenced if it is a symbolic link.
• **fchown**() changes the ownership of the file referred to by the
open file descriptor _fd_.
• **lchown**() is like **chown**(), but does not dereference symbolic
links.
Only a privileged process (Linux: one with the **CAP_CHOWN**
capability) may change the owner of a file. The owner of a file
may change the group of the file to any group of which that owner
is a member. A privileged process (Linux: with **CAP_CHOWN**) may
change the group arbitrarily.
If the _owner_ or _group_ is specified as -1, then that ID is not
changed.
When the owner or group of an executable file is changed by an
unprivileged user, the **S_ISUID** and **S_ISGID** mode bits are cleared.
POSIX does not specify whether this also should happen when root
does the **chown**(); the Linux behavior depends on the kernel
version, and since Linux 2.2.13, root is treated like other
users. In case of a non-group-executable file (i.e., one for
which the **S_IXGRP** bit is not set) the **S_ISGID** bit indicates
mandatory locking, and is not cleared by a **chown**().
When the owner or group of an executable file is changed (by any
user), all capability sets for the file are cleared.fchownat() The fchownat() system call operates in exactly the same way as chown(), except for the differences described here.
If the pathname given in _pathname_ is relative, then it is
interpreted relative to the directory referred to by the file
descriptor _dirfd_ (rather than relative to the current working
directory of the calling process, as is done by **chown**() for a
relative pathname).
If _pathname_ is relative and _dirfd_ is the special value **AT_FDCWD**,
then _pathname_ is interpreted relative to the current working
directory of the calling process (like **chown**()).
If _pathname_ is absolute, then _dirfd_ is ignored.
The _flags_ argument is a bit mask created by ORing together 0 or
more of the following values;
**AT_EMPTY_PATH** (since Linux 2.6.39)
If _pathname_ is an empty string, operate on the file
referred to by _dirfd_ (which may have been obtained using
the [open(2)](../man2/open.2.html) **O_PATH** flag). In this case, _dirfd_ can refer
to any type of file, not just a directory. If _dirfd_ is
**AT_FDCWD**, the call operates on the current working
directory. This flag is Linux-specific; define
**_GNU_SOURCE** to obtain its definition.
**AT_SYMLINK_NOFOLLOW**
If _pathname_ is a symbolic link, do not dereference it:
instead operate on the link itself, like **lchown**(). (By
default, **fchownat**() dereferences symbolic links, like
**chown**().)
See [openat(2)](../man2/openat.2.html) for an explanation of the need for **fchownat**().RETURN VALUE top
On success, zero is returned. On error, -1 is returned, and
_[errno](../man3/errno.3.html)_ is set to indicate the error.ERRORS top
Depending on the filesystem, errors other than those listed below
can be returned.
The more general errors for **chown**() are listed below.
**EACCES** Search permission is denied on a component of the path
prefix. (See also [path_resolution(7)](../man7/path%5Fresolution.7.html).)
**EBADF** (**fchown**()) _fd_ is not a valid open file descriptor.
**EBADF** (**fchownat**()) _pathname_ is relative but _dirfd_ is neither
**AT_FDCWD** nor a valid file descriptor.
**EFAULT** _pathname_ points outside your accessible address space.
**EINVAL** (**fchownat**()) Invalid flag specified in _flags_.
**EIO** (**fchown**()) A low-level I/O error occurred while modifying
the inode.
**ELOOP** Too many symbolic links were encountered in resolving
_pathname_.
**ENAMETOOLONG**
_pathname_ is too long.
**ENOENT** The file does not exist.
**ENOMEM** Insufficient kernel memory was available.
**ENOTDIR**
A component of the path prefix is not a directory.
**ENOTDIR**
(**fchownat**()) _pathname_ is relative and _dirfd_ is a file
descriptor referring to a file other than a directory.
**EPERM** The calling process did not have the required permissions
(see above) to change owner and/or group.
**EPERM** The file is marked immutable or append-only. (See
[FS_IOC_SETFLAGS(2const)](../man2/FS%5FIOC%5FSETFLAGS.2const.html).)
**EROFS** The named file resides on a read-only filesystem.VERSIONS top
The 4.4BSD version can be used only by the superuser (that is,
ordinary users cannot give away files).STANDARDS top
POSIX.1-2008.HISTORY top
**chown**()
**fchown**()
**lchown**()
4.4BSD, SVr4, POSIX.1-2001.
**fchownat**()
POSIX.1-2008. Linux 2.6.16, glibc 2.4.NOTES top
Ownership of new files When a new file is created (by, for example, open(2) or mkdir(2)), its owner is made the same as the filesystem user ID of the creating process. The group of the file depends on a range of factors, including the type of filesystem, the options used to mount the filesystem, and whether or not the set-group-ID mode bit is enabled on the parent directory. If the filesystem supports the -o grpid (or, synonymously -o bsdgroups) and -o nogrpid (or, synonymously -o sysvgroups) mount(8) options, then the rules are as follows:
• If the filesystem is mounted with **-o grpid**, then the group of
a new file is made the same as that of the parent directory.
• If the filesystem is mounted with **-o nogrpid** and the set-
group-ID bit is disabled on the parent directory, then the
group of a new file is made the same as the process's
filesystem GID.
• If the filesystem is mounted with **-o nogrpid** and the set-
group-ID bit is enabled on the parent directory, then the
group of a new file is made the same as that of the parent
directory.
As at Linux 4.12, the **-o grpid** and **-o nogrpid** mount options are
supported by ext2, ext3, ext4, and XFS. Filesystems that don't
support these mount options follow the **-o nogrpid** rules.glibc notes On older kernels where fchownat() is unavailable, the glibc wrapper function falls back to the use of chown() and lchown(). When pathname is a relative pathname, glibc constructs a pathname based on the symbolic link in /proc/self/fd that corresponds to the dirfd argument.
NFS The chown() semantics are deliberately violated on NFS filesystems which have UID mapping enabled. Additionally, the semantics of all system calls which access the file contents are violated, because chown() may cause immediate access revocation on already open files. Client side caching may lead to a delay between the time where ownership have been changed to allow access for a user and the time where the file can actually be accessed by the user on other clients.
Historical details The original Linux chown(), fchown(), and lchown() system calls supported only 16-bit user and group IDs. Subsequently, Linux 2.4 added chown32(), fchown32(), and lchown32(), supporting 32-bit IDs. The glibc chown(), fchown(), and lchown() wrapper functions transparently deal with the variations across kernel versions.
Before Linux 2.1.81 (except 2.1.46), **chown**() did not follow
symbolic links. Since Linux 2.1.81, **chown**() does follow symbolic
links, and there is a new system call **lchown**() that does not
follow symbolic links. Since Linux 2.1.86, this new call (that
has the same semantics as the old **chown**()) has got the same
syscall number, and **chown**() got the newly introduced number.EXAMPLES top
The following program changes the ownership of the file named in
its second command-line argument to the value specified in its
first command-line argument. The new owner can be specified
either as a numeric user ID, or as a username (which is converted
to a user ID by using [getpwnam(3)](../man3/getpwnam.3.html) to perform a lookup in the
system password file).Program source #include <pwd.h> #include <stdio.h> #include <stdlib.h> #include <sys/types.h> #include <unistd.h>
int
main(int argc, char *argv[])
{
char *endptr;
uid_t uid;
struct passwd *pwd;
if (argc != 3 || argv[1][0] == '\0') {
fprintf(stderr, "%s <owner> <file>\n", argv[0]);
exit(EXIT_FAILURE);
}
uid = strtol(argv[1], &endptr, 10); /* Allow a numeric string */
if (*endptr != '\0') { /* Was not pure numeric string */
pwd = getpwnam(argv[1]); /* Try getting UID for username */
if (pwd == NULL) {
perror("getpwnam");
exit(EXIT_FAILURE);
}
uid = pwd->pw_uid;
}
if (chown(argv[2], uid, -1) == -1) {
perror("chown");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}SEE ALSO top
[chgrp(1)](../man1/chgrp.1.html), [chown(1)](../man1/chown.1.html), [chmod(2)](../man2/chmod.2.html), [flock(2)](../man2/flock.2.html), [path_resolution(7)](../man7/path%5Fresolution.7.html),
[symlink(7)](../man7/symlink.7.html)COLOPHON top
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man-pages@man7.orgLinux man-pages 6.9.1 2024-06-15 chown(2)
Pages that refer to this page:chgrp(1), chown(1), access(2), chmod(2), fcntl(2), mkdir(2), mknod(2), mount_setattr(2), open(2), open_by_handle_at(2), stat(2), statx(2), symlink(2), syscalls(2), euidaccess(3), fpathconf(3), id_t(3type), shm_open(3), systemd.exec(5), capabilities(7), inode(7), inotify(7), landlock(7), shm_overview(7), signal-safety(7), spufs(7), symlink(7), unix(7)