CHMOD(2) | System Calls Manual | CHMOD(2) |
chmod
, lchmod
,
fchmod
, fchmodat
—
#include <sys/stat.h>
int
chmod
(const
char *path, mode_t
mode);
int
lchmod
(const
char *path, mode_t
mode);
int
fchmod
(int
fd, mode_t
mode);
#include
<sys/stat.h>
#include <fcntl.h>
int
fchmodat
(int
fd, const char
*path, mode_t mode,
int flag);
chmod
() sets the file permission bits of
the file specified by the pathname path to
mode. fchmod
() sets the
permission bits of the specified file descriptor fd.
lchmod
() is like chmod
()
except in the case where the named file is a symbolic link, in which case
lchmod
() sets the permission bits of the link, while
chmod
() sets the bits of the file the link references.
fchmodat
() works the same way as
chmod
() (or lchmod
() if
AT_SYMLINK_NOFOLLOW
is set in
flag) except if path is
relative. In that case, it is looked up from a directory whose file
descriptor was passed as fd. Search permission is
required on this directory. fd except if that file
descriptor was opened with the O_SEARCH
flag.
fd can be set to AT_FDCWD
in
order to specify the current directory.
chmod
() verifies that the process owner
(user) either owns the file specified by path (or
fd), or is the super-user. A mode is created from
or'd permission bit masks defined in
<sys/stat.h>
:
#define S_IRWXU 0000700 /* RWX mask for owner */ #define S_IRUSR 0000400 /* R for owner */ #define S_IWUSR 0000200 /* W for owner */ #define S_IXUSR 0000100 /* X for owner */ #define S_IRWXG 0000070 /* RWX mask for group */ #define S_IRGRP 0000040 /* R for group */ #define S_IWGRP 0000020 /* W for group */ #define S_IXGRP 0000010 /* X for group */ #define S_IRWXO 0000007 /* RWX mask for other */ #define S_IROTH 0000004 /* R for other */ #define S_IWOTH 0000002 /* W for other */ #define S_IXOTH 0000001 /* X for other */ #define S_ISUID 0004000 /* set user id on execution */ #define S_ISGID 0002000 /* set group id on execution */ #define S_ISVTX 0001000 /* sticky bit */
The mode ISVTX
(the ‘sticky
bit’) can be set on regular files, but has no effect. For historical
reasons this can be done only by the super-user.
If mode ISVTX
(the ‘sticky
bit’) is set on a directory, an unprivileged user may not delete or
rename files of other users in that directory. The sticky bit may be set by
any user on a directory which the user owns or has appropriate
permissions.
For more information about the history and properties of the sticky bit, see sticky(7).
Changing the owner of a file turns off the set-user-id and set-group-id bits; writing to a file turns off the set-user-id and set-group-id bits unless the user is the super-user. This makes the system somewhat more secure by protecting set-user-id (set-group-id) files from remaining set-user-id (set-group-id) if they are modified, at the expense of a degree of compatibility.
chmod
(), lchmod
(),
fchmod
(), and fchmodat
()
functions return the value 0 if successful; otherwise the
value -1 is returned and the global variable
errno is set to indicate the error.
chmod
(), lchmod
() and
fchmodat
() will fail and the file mode will be
unchanged if:
EACCES
]EFAULT
]EFTYPE
]S_ISVTX
), and path does not
refer to a directory.EIO
]ELOOP
]ENAMETOOLONG
]NAME_MAX
}
characters, or an entire path name exceeded
{PATH_MAX
} characters.ENOENT
]ENOTDIR
]EPERM
]S_ISGID
) but the file's group is neither the
effective group ID nor is it in the group access list.EROFS
]In addition, fchmodat
() will fail if:
EBADF
]AT_FDCWD
nor a
valid file descriptor open for reading or searching.ENOTDIR
]fchmod
() will fail if:
EBADF
]EFTYPE
]S_ISVTX
), and fd does not
refer to a directory.EINVAL
]EIO
]EPERM
]S_ISGID
) but the file's group is neither the
effective group ID nor is it in the group access list.EROFS
]chmod
() function conforms to IEEE
Std 1003.1-1990 (“POSIX.1”).
fchmodat
() function conforms to IEEE
Std 1003.1-2008 (“POSIX.1”).
chmod
() function call appeared in
Version 1 AT&T UNIX. The
fchmod
() function call appeared in
4.2BSD. The lchmod
() function
call appeared in NetBSD 1.3.
September 1, 2019 | NetBSD 9.0 |