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chmod
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<p>chmod is a <a href="/facts/Shell_(computing)/Sa67elS7">shell</a> <a href="/facts/Command_(computing)/zUrvQbFy">command</a> for changing <a href="/facts/File-system_permissions/DHq5SwI4">access permissions</a> and special mode flags of <a href="/facts/Computer_file/FjFH3Ufm">files</a> (including <a href="/facts/Unix_file_type/CplllKdU">special files</a> such as <a href="/facts/Computer_directory/VLtLcEXY">directories</a>). The name is short for <i>change mode</i> where <i>mode</i> refers to the permissions and flags collectively. </p><p>The command originated in <a href="/facts/Research_Unix/5oWmUdwo">AT&T Unix</a> version 1 and was exclusive to <a href="/facts/Unix/0pNL2seI">Unix</a> and <a href="/facts/Unix-like/YAKrAxzd">Unix-like</a> <a href="/facts/Operating_system/8XTuvMh2">operating systems</a> until it was ported to other operating systems such as <a href="/facts/Microsoft_Windows/bwhAhuSL">Windows</a> (in <a href="/facts/UnxUtils/CsUBGmUM">UnxUtils</a>) and <a href="/facts/IBM_i/lsIRAUvn">IBM i</a>. </p><p>In <a href="/facts/Unix/0pNL2seI">Unix</a> and <a href="/facts/Unix-like/YAKrAxzd">Unix-like</a> operating systems, a <a href="/facts/System_call/NW44AFJr">system call</a> with the same name as the command, chmod(), provides access to the underlying access control data. The command exposes the capabilities of the system call to a shell user. </p><p>As the need for enhanced <a href="/facts/File-system_permissions/DHq5SwI4">file-system permissions</a> grew, <a href="/facts/Access-control_list/t38J9Vao">access-control lists</a> were added to many file systems to augment the modes controlled via chmod. </p><p>The implementation of chmod bundled in <a href="/facts/GNU_Core_Utilities/Q9cop5U5">GNU coreutils</a> was written by David MacKenzie and Jim Meyering. </p>