| <html lang="en"> |
| <head> |
| <title>File Owner - The GNU C Library</title> |
| <meta http-equiv="Content-Type" content="text/html"> |
| <meta name="description" content="The GNU C Library"> |
| <meta name="generator" content="makeinfo 4.13"> |
| <link title="Top" rel="start" href="index.html#Top"> |
| <link rel="up" href="File-Attributes.html#File-Attributes" title="File Attributes"> |
| <link rel="prev" href="Testing-File-Type.html#Testing-File-Type" title="Testing File Type"> |
| <link rel="next" href="Permission-Bits.html#Permission-Bits" title="Permission Bits"> |
| <link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage"> |
| <!-- |
| This file documents the GNU C library. |
| |
| This is Edition 0.12, last updated 2007-10-27, |
| of `The GNU C Library Reference Manual', for version |
| 2.8 (Sourcery G++ Lite 2011.03-41). |
| |
| Copyright (C) 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, |
| 2003, 2007, 2008, 2010 Free Software Foundation, Inc. |
| |
| Permission is granted to copy, distribute and/or modify this document |
| under the terms of the GNU Free Documentation License, Version 1.3 or |
| any later version published by the Free Software Foundation; with the |
| Invariant Sections being ``Free Software Needs Free Documentation'' |
| and ``GNU Lesser General Public License'', the Front-Cover texts being |
| ``A GNU Manual'', and with the Back-Cover Texts as in (a) below. A |
| copy of the license is included in the section entitled "GNU Free |
| Documentation License". |
| |
| (a) The FSF's Back-Cover Text is: ``You have the freedom to |
| copy and modify this GNU manual. Buying copies from the FSF |
| supports it in developing GNU and promoting software freedom.''--> |
| <meta http-equiv="Content-Style-Type" content="text/css"> |
| <style type="text/css"><!-- |
| pre.display { font-family:inherit } |
| pre.format { font-family:inherit } |
| pre.smalldisplay { font-family:inherit; font-size:smaller } |
| pre.smallformat { font-family:inherit; font-size:smaller } |
| pre.smallexample { font-size:smaller } |
| pre.smalllisp { font-size:smaller } |
| span.sc { font-variant:small-caps } |
| span.roman { font-family:serif; font-weight:normal; } |
| span.sansserif { font-family:sans-serif; font-weight:normal; } |
| --></style> |
| <link rel="stylesheet" type="text/css" href="../cs.css"> |
| </head> |
| <body> |
| <div class="node"> |
| <a name="File-Owner"></a> |
| <p> |
| Next: <a rel="next" accesskey="n" href="Permission-Bits.html#Permission-Bits">Permission Bits</a>, |
| Previous: <a rel="previous" accesskey="p" href="Testing-File-Type.html#Testing-File-Type">Testing File Type</a>, |
| Up: <a rel="up" accesskey="u" href="File-Attributes.html#File-Attributes">File Attributes</a> |
| <hr> |
| </div> |
| |
| <h4 class="subsection">14.9.4 File Owner</h4> |
| |
| <p><a name="index-file-owner-1530"></a><a name="index-owner-of-a-file-1531"></a><a name="index-group-owner-of-a-file-1532"></a> |
| Every file has an <dfn>owner</dfn> which is one of the registered user names |
| defined on the system. Each file also has a <dfn>group</dfn> which is one of |
| the defined groups. The file owner can often be useful for showing you |
| who edited the file (especially when you edit with GNU Emacs), but its |
| main purpose is for access control. |
| |
| <p>The file owner and group play a role in determining access because the |
| file has one set of access permission bits for the owner, another set |
| that applies to users who belong to the file's group, and a third set of |
| bits that applies to everyone else. See <a href="Access-Permission.html#Access-Permission">Access Permission</a>, for the |
| details of how access is decided based on this data. |
| |
| <p>When a file is created, its owner is set to the effective user ID of the |
| process that creates it (see <a href="Process-Persona.html#Process-Persona">Process Persona</a>). The file's group ID |
| may be set to either the effective group ID of the process, or the group |
| ID of the directory that contains the file, depending on the system |
| where the file is stored. When you access a remote file system, it |
| behaves according to its own rules, not according to the system your |
| program is running on. Thus, your program must be prepared to encounter |
| either kind of behavior no matter what kind of system you run it on. |
| |
| <p><a name="index-chown-1533"></a><a name="index-chgrp-1534"></a>You can change the owner and/or group owner of an existing file using |
| the <code>chown</code> function. This is the primitive for the <code>chown</code> |
| and <code>chgrp</code> shell commands. |
| |
| <p><a name="index-unistd_002eh-1535"></a>The prototype for this function is declared in <samp><span class="file">unistd.h</span></samp>. |
| |
| <!-- unistd.h --> |
| <!-- POSIX.1 --> |
| <div class="defun"> |
| — Function: int <b>chown</b> (<var>const char *filename, uid_t owner, gid_t group</var>)<var><a name="index-chown-1536"></a></var><br> |
| <blockquote><p>The <code>chown</code> function changes the owner of the file <var>filename</var> to |
| <var>owner</var>, and its group owner to <var>group</var>. |
| |
| <p>Changing the owner of the file on certain systems clears the set-user-ID |
| and set-group-ID permission bits. (This is because those bits may not |
| be appropriate for the new owner.) Other file permission bits are not |
| changed. |
| |
| <p>The return value is <code>0</code> on success and <code>-1</code> on failure. |
| In addition to the usual file name errors (see <a href="File-Name-Errors.html#File-Name-Errors">File Name Errors</a>), |
| the following <code>errno</code> error conditions are defined for this function: |
| |
| <dl> |
| <dt><code>EPERM</code><dd>This process lacks permission to make the requested change. |
| |
| <p>Only privileged users or the file's owner can change the file's group. |
| On most file systems, only privileged users can change the file owner; |
| some file systems allow you to change the owner if you are currently the |
| owner. When you access a remote file system, the behavior you encounter |
| is determined by the system that actually holds the file, not by the |
| system your program is running on. |
| |
| <p>See <a href="Options-for-Files.html#Options-for-Files">Options for Files</a>, for information about the |
| <code>_POSIX_CHOWN_RESTRICTED</code> macro. |
| |
| <br><dt><code>EROFS</code><dd>The file is on a read-only file system. |
| </dl> |
| </p></blockquote></div> |
| |
| <!-- unistd.h --> |
| <!-- BSD --> |
| <div class="defun"> |
| — Function: int <b>fchown</b> (<var>int filedes, int owner, int group</var>)<var><a name="index-fchown-1537"></a></var><br> |
| <blockquote><p>This is like <code>chown</code>, except that it changes the owner of the open |
| file with descriptor <var>filedes</var>. |
| |
| <p>The return value from <code>fchown</code> is <code>0</code> on success and <code>-1</code> |
| on failure. The following <code>errno</code> error codes are defined for this |
| function: |
| |
| <dl> |
| <dt><code>EBADF</code><dd>The <var>filedes</var> argument is not a valid file descriptor. |
| |
| <br><dt><code>EINVAL</code><dd>The <var>filedes</var> argument corresponds to a pipe or socket, not an ordinary |
| file. |
| |
| <br><dt><code>EPERM</code><dd>This process lacks permission to make the requested change. For details |
| see <code>chmod</code> above. |
| |
| <br><dt><code>EROFS</code><dd>The file resides on a read-only file system. |
| </dl> |
| </p></blockquote></div> |
| |
| </body></html> |
| |
