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CHOWN(3P)                  POSIX Programmer's Manual                 CHOWN(3P)

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 - change owner and group of a file
SYNOPSIS
       #include <unistd.h>
       int chown(const char *path, uid_t owner, gid_t group);

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 success-
       ful 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, respec-
       tively, the corresponding ID of the file shall not be changed. If  both
       owner and group are -1, the times need not be updated.
       Upon  successful completion, chown() shall mark for update the st_ctime
       field of the file.
RETURN VALUE
       Upon successful completion, 0 shall be returned; otherwise, -1 shall be
       returned  and  errno  set  to indicate the error. If -1 is returned, no
       changes are made in the user ID and group ID of the file.
ERRORS
       The chown() function 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 the path argument exceeds {PATH_MAX} or a pathname
              component is longer than {NAME_MAX}.
       ENOTDIR
              A component of the path prefix is not a directory.
       ENOENT A component of path does not name an existing file or path is an
              empty string.
       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 chown() function may fail if:
       EIO    An I/O error occurred while reading or writing to the file  sys-
              tem.
       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
              As a result of encountering a symbolic link in resolution of the
              path  argument,  the  length  of the substituted pathname string
              exceeded {PATH_MAX}.

       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 secu-
       rity 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 confin-
       ing.  This  volume  of  IEEE Std 1003.1-2001  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 manda-
       tory 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.
FUTURE DIRECTIONS
       None.
SEE ALSO
       chmod(),     pathconf(),     the    Base    Definitions    volume    of
       IEEE Std 1003.1-2001, <sys/types.h>, <unistd.h>
COPYRIGHT
       Portions of this text are reprinted and reproduced in  electronic  form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX),  The  Open  Group  Base
       Specifications  Issue  6,  Copyright  (C) 2001-2003 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 .

IEEE/The Open Group                  2003                            CHOWN(3P)