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| <h4 class="subsection">14.9.6 How Your Access to a File is Decided</h4> |
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| <p><a name="index-permission-to-access-a-file-1559"></a><a name="index-access-permission-for-a-file-1560"></a><a name="index-file-access-permission-1561"></a> |
| Recall that the operating system normally decides access permission for |
| a file based on the effective user and group IDs of the process and its |
| supplementary group IDs, together with the file's owner, group and |
| permission bits. These concepts are discussed in detail in <a href="Process-Persona.html#Process-Persona">Process Persona</a>. |
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| <p>If the effective user ID of the process matches the owner user ID of the |
| file, then permissions for read, write, and execute/search are |
| controlled by the corresponding “user” (or “owner”) bits. Likewise, |
| if any of the effective group ID or supplementary group IDs of the |
| process matches the group owner ID of the file, then permissions are |
| controlled by the “group” bits. Otherwise, permissions are controlled |
| by the “other” bits. |
| |
| <p>Privileged users, like ‘<samp><span class="samp">root</span></samp>’, can access any file regardless of |
| its permission bits. As a special case, for a file to be executable |
| even by a privileged user, at least one of its execute bits must be set. |
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