PROLOG

       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.

NAME

       chown, fchownat — change owner and group of a file

SYNOPSIS

       #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);

DESCRIPTION

       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.

RETURN VALUE

       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.

ERRORS

       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.

EXAMPLES

       None.

APPLICATION USAGE

       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.

RATIONALE

       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.

FUTURE DIRECTIONS

       None.

SEE ALSO

       chmod(), fpathconf(), lchown()

       The Base Definitions volume of POSIX.1‐2017, <fcntl.h>, <sys_types.h>, <unistd.h>

COPYRIGHT

       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 .

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