| 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 9.3 |