ln (Unix)

<h2 id="versions">Versions</h2>
ln appeared in Issue 2 of the <a href="/facts/X%2fOpen/btwVKbX2">X/Open</a> Portability Guidelines.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The version of ln bundled in <a href="/facts/GNU/HlAKKBdt">GNU</a> <a href="/facts/Coreutils/Q9cop5U5">coreutils</a> was written by Mike Parker and David MacKenzie.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
The command is available as a separate package for <a href="/facts/Microsoft_Windows/bwhAhuSL">Microsoft Windows</a> as part of the <a href="/facts/UnxUtils/CsUBGmUM">UnxUtils</a> collection of <a href="/facts/Native_(computing)/yNez4jAK">native</a> <a href="/facts/Windows_API/RRw4RtTu">Win32</a> <a href="/facts/Porting/7s6tFs8B">ports</a> of common GNU Unix-like utilities.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> The ln command has also been ported to the <a href="/facts/IBM_i/lsIRAUvn">IBM i</a> operating system.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a>

<h2 id="links">Links</h2>
Links allow more than one filename to refer to the same file as in the case of a <a href="/facts/Hard_link/Twqdfvlt">hard link</a> or act as <a href="/facts/Reference_(computer_science)/1vm2Bph1">pointers</a> to a filename as in the case of a <a href="/facts/Symbolic_link/laB0S68t">soft link</a>. Both hard links and soft links can be created by the ln command. Specifically,

<ol><li><a href="/facts/Hard_link/Twqdfvlt">Hard links</a>, also known simply as links, are objects that associate the filename with the <a href="/facts/Inode/Ej7JIzyP">inode</a>, and therefore the file contents itself.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> A given file on disk could have multiple links scattered through the <a href="/facts/Directory_structure/t7lEWPpd">directory hierarchy</a>, with all of the links being equivalent since they all associate with the same <a href="/facts/Inode/Ej7JIzyP">inode</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> Creating a link therefore does not copy the contents of the file but merely causes another name to be associated with the same contents. Each time a hard link is created, a <a href="/facts/Reference_counting/jbPcXuXe">link counter</a> that is a part of the <a href="/facts/Inode/Ej7JIzyP">inode structure</a> gets incremented; a file is not deleted until its reference count reaches zero.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a><a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> However, hard links can only be created on the same <a href="/facts/File_system/FdPm90uc">file system</a>; this can prove to be a disadvantage.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a></li>
<li><a href="/facts/Symbolic_link/laB0S68t">Symbolic links</a> are special files which, when encountered during pathname resolution, modify the <a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13">pathname resolution</a> to be taken to the location which the symbolic link contains. The content of the symbolic link is therefore the destination <a href="/facts/Path_(computing)/F5wNAuMY">path</a> string, which can also be examined using the readlink command line utility.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a> The symbolic link may contain an arbitrary string which does not refer to the location of an existing file. Such a symbolic link will fail until a file is created at the location which is contained by the symbolic link. By contrast, a symbolic link to an existing file will fail if the existing file is moved to a different location (or renamed).<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a></li></ol>
<h2 id="specification">Specification</h2>
The ln utility on systems compliant with the <a href="/facts/Single_Unix_Specification/w1ba5bDt">Single Unix Specification</a> is specified in the Shell and Utilities (XCU) document, which forms a part of the Single Unix Specification.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a> A mostly identical document is part of <a href="/facts/POSIX/mQkSt234">POSIX</a>.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a>
The specification describes two ways of invoking the ln utility. Specifically,

In the "single file" invocation the ln utility creates a new hard link (directory entry) for the source file specified by the source_file operand at the destination path specified by the target_file operand. However, if the -s option is specified, a symbolic link is created.
ln [-fs] [-L|-P] source_file target_file

In the "multiple file" invocation the ln utility creates a new hard link (<a href="http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap03.html#tag_03_130">directory entry</a>), or if the -s option is specified, a symbolic link, for each file specified by the source_file operand, at a destination path in an existing directory named by operand target_dir.
ln [-fs] [-L|-P] source_file_1 source_file_2 ... target_dir

The specification also specifies the command line options that must be supported:

-f Force existing destination pathnames to be removed to allow the link.
-L For each source_file operand that names a file that is a symbolic link, create a hard link to the file referenced by the symbolic link.
-P For each source_file operand that names a file that is a symbolic link, create a (hard) link to the symbolic link itself.
-s Create symbolic links instead of hard links. If the -s option is specified, the -L and -P options are silently ignored.
If more than one of the mutually-exclusive options -L and -P is specified the last option specified determines the behavior of the utility.
If the -s option is not specified and neither a -L nor a -P option is specified, the implementation defines which of the -L and -P options will be used as the default.
If neither target file nor target directory are specified, links will be created in the current <a href="/facts/Working_directory/2qI00r0z">working directory</a>.

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/List_of_Unix_commands/EEuIsUx9">List of Unix commands</a></li>
<li><a href="/facts/NTFS_junction_point/YcjbI05N">NTFS junction point</a></li></ul>

<h2 id="external-links">External links</h2>

The Wikibook Guide to Unix has a page on the topic of: File System Utilities - ln

<ul><li><a href="https://linux.die.net/man/1/ln">ln(1)</a> – <a href="/facts/Linux/9FvCKSTq">Linux</a> User Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a></li>
<li><a href="https://www.freebsd.org/cgi/man.cgi?query=ln&sektion=1">ln(1)</a> – <a href="/facts/FreeBSD/RKsFTm7F">FreeBSD</a> General Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a></li>
<li><a href="https://man.netbsd.org/ln.1">ln(1)</a> – <a href="/facts/NetBSD/PTm5HWls">NetBSD</a> General Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a></li>
<li><a href="https://man.openbsd.org/ln.1">ln(1)</a> – <a href="/facts/OpenBSD/xmPS9tek">OpenBSD</a> General Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a></li>
<li><a href="https://keith.github.io/xcode-man-pages/ln.1.html">ln(1)</a> – <a href="/facts/Darwin_(operating_system)/DogI3ptd">Darwin</a> and <a href="/facts/MacOS/Y93vVpTm">macOS</a> General Commands <a href="/facts/Man_page/S2yYjy0J">Manual</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Kernighan, Brian W.; Pike, Rob (1984). The Unix programming environment. Englewood Cliffs, N.J.: Prentice-Hall. p. 59. ISBN 013937681X. <a href="013937681X" target="_blank">013937681X</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"GNU Coreutils: ln invocation". gnu.org. Free Software Foundation, Inc. Retrieved 7 August 2015. <a href="https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html" target="_blank">https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">"ln - The Open Group Base Specifications Issue 7". pubs.opengroup.org. The IEEE and The Open Group. Retrieved 7 August 2015. <a href="http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html" target="_blank">http://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"Why are hard links not allowed to directories in UNIX/Linux?". unix.stackexchange.com. Retrieved 7 August 2015. <a href="http://unix.stackexchange.com/questions/22394/why-hard-links-not-allowed-to-directories-in-unix-linux?rq=1" target="_blank">http://unix.stackexchange.com/questions/22394/why-hard-links-not-allowed-to-directories-in-unix-linux?rq=1</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"GNU Coreutils: ln invocation". gnu.org. Free Software Foundation, Inc. Retrieved 7 August 2015. <a href="https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html" target="_blank">https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">ln – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group <a href="https://pubs.opengroup.org/onlinepubs/9799919799/utilities/ln.html" target="_blank">https://pubs.opengroup.org/onlinepubs/9799919799/utilities/ln.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">ln(1) – Linux General Commands Manual <a href="https://www.mankier.com/1/ln" target="_blank">https://www.mankier.com/1/ln</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">"Native Win32 ports of some GNU utilities". unxutils.sourceforge.net. <a href="http://unxutils.sourceforge.net/" target="_blank">http://unxutils.sourceforge.net/</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">IBM. "IBM System i Version 7.2 Programming Qshell" (PDF). IBM. Retrieved 2020-09-05. <a href="/wiki/IBM" target="_blank">/wiki/IBM</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Kernighan, Brian W.; Pike, Rob (1984). The Unix programming environment. Englewood Cliffs, N.J.: Prentice-Hall. p. 59. ISBN 013937681X. <a href="013937681X" target="_blank">013937681X</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Loosemore, Sandra; Stallman, Richard M.; McGrath, Roland; Oram, Andrew; Drepper, Ulrich. The GNU C Library Reference Manual (PDF). Free Software Foundation, Inc. p. 392. Retrieved 7 August 2015. <a href="https://www.gnu.org/software/libc/manual/pdf/libc.pdf" target="_blank">https://www.gnu.org/software/libc/manual/pdf/libc.pdf</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Kernighan, Brian W.; Pike, Rob (1984). The Unix programming environment. Englewood Cliffs, N.J.: Prentice-Hall. p. 59. ISBN 013937681X. <a href="013937681X" target="_blank">013937681X</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">"Speaking UNIX: It is all about the inode". ibm.com. IBM developerWorks. Retrieved 7 August 2015. <a href="http://www.ibm.com/developerworks/aix/library/au-speakingunix14/" target="_blank">http://www.ibm.com/developerworks/aix/library/au-speakingunix14/</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Bovet, Daniel P.; Cesati, Marco (2005). Understanding the Linux Kernel (3rd ed.). Boston, MA: Safari Tech Books Online. p. 14. ISBN 0596005652. <a href="0596005652" target="_blank">0596005652</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">"readlink(1) - Linux man page". linux.die.net. Retrieved 7 August 2015. <a href="http://linux.die.net/man/1/readlink" target="_blank">http://linux.die.net/man/1/readlink</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Loosemore, Sandra; Stallman, Richard M.; McGrath, Roland; Oram, Andrew; Drepper, Ulrich. The GNU C Library Reference Manual (PDF). Free Software Foundation, Inc. p. 392. Retrieved 7 August 2015. <a href="https://www.gnu.org/software/libc/manual/pdf/libc.pdf" target="_blank">https://www.gnu.org/software/libc/manual/pdf/libc.pdf</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">"The Single UNIX Specification, Version 4 - Overview". unix.org. unix.org. Retrieved 7 August 2015. <a href="http://www.unix.org/version4/overview.html" target="_blank">http://www.unix.org/version4/overview.html</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">ln – Shell and Utilities Reference, The Single UNIX Specification, Version 4 from The Open Group <a href="https://pubs.opengroup.org/onlinepubs/9799919799/utilities/ln.html" target="_blank">https://pubs.opengroup.org/onlinepubs/9799919799/utilities/ln.html</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
</ol>

ln (Unix) open-in-new

ln (Unix)