ln (Unix)

A link allows more than one path to refer to the same file.

A hard link is a directory entry that refers to a file's inode (an internal reference). A file can have multiple hard links {{endash}} each referring to the same inode. Creating a hard link does not copy the contents of the file; but merely causes another name to be associated with the same content. When a hard link is created for a file, a counter in its inode is incremented, and removing a hard link results in decrementing the counter. A file is not deleted (to allow reusing its storage space) until its reference count reaches zero.{{cite web|title=Speaking UNIX: It is all about the inode|url=http://www.ibm.com/developerworks/aix/library/au-speakingunix14/|website=ibm.com|publisher=IBM developerWorks|access-date=7 August 2015}} A hard link can only refer to an object on the same file system.{{cite book|last1=Bovet|first1=Daniel P.|last2=Cesati|first2=Marco|title=Understanding the Linux Kernel|date=2005|publisher=Safari Tech Books Online|location=Boston, MA|isbn=0596005652|page=14|edition=3rd}}

A symbolic link refers to another file by its path (a symbolic reference).{{cite web|title=GNU Coreutils: ln invocation|url=https://www.gnu.org/software/coreutils/manual/html_node/ln-invocation.html|website=gnu.org|publisher=Free Software Foundation, Inc.|access-date=7 August 2015}} When encountered during pathname resolution, modify the [http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap04.html#tag_04_13 pathname resolution] to be taken to the location which the symbolic link contains. The content of a symbolic link is the target path, which can also be examined via the {{code|readlink}} command.{{cite web|title=readlink(1) - Linux man page|url=http://linux.die.net/man/1/readlink|website=linux.die.net|access-date=7 August 2015|ref=ReadlinkMan}} A symbolic link may specify a path that does not refer to an existing file. Resolving such a symbolic link will fail until a file is created at its specified path. Also, a symbolic link to an existing file will fail to resolve if the file is moved.{{cite book|last1=Loosemore|first1=Sandra|last2=Stallman|first2=Richard M.|last3=McGrath|first3=Roland|last4=Oram|first4=Andrew|last5=Drepper|first5=Ulrich|title=The GNU C Library Reference Manual|publisher=Free Software Foundation, Inc|page=392|url=https://www.gnu.org/software/libc/manual/pdf/libc.pdf|access-date=7 August 2015}}

Per the Single Unix Specification, the {{code|ln}} command is specified in the Shell and Utilities (XCU) document.{{cite web|title=The Single UNIX Specification, Version 4 - Overview|url=http://www.unix.org/version4/overview.html|website=unix.org|publisher=unix.org|access-date=7 August 2015}} POSIX includes a similar specification.{{man|1|ln|SUS}}

If neither target file nor target directory are specified, links are created in the current working directory.

The specification indicates command line options that must be supported:

• {{code|-f}} (force) Clobbers an existing file if the output path specifies an existing file
• {{code|-L}} If a source operand specifies a symbolic link, create a hard link to the link's target file
• {{code|-P}} If a source operand specifies a symbolic link, create a hard link to the symbolic link file
• {{code|-s}} Create symbolic links instead of hard links; causes {{code|-L}} and {{code|-P}} to be silently ignored

If more than one of the mutually-exclusive options {{code|-L}} and {{code|-P}} is specified, the last option specified determines the resulting behavior.

If the {{code|-s}} option is not specified and neither a {{code|-L}} nor a {{code|-P}} option is specified, the implementation defines which of the {{code|-L}} and {{code|-P}} options is used by default.

The command creates a new link to the path indicated by {{code|source}}; stored at the path indicated by {{code|target}}. The syntax is as follows:

ln [-fs] [-L|-P] source target

The command creates a new link to each file specified by the {{code|source_#}} operands; stored in an existing directory indicated by {{code|target_dir}}.

ln [-fs] [-L|-P] source_1 source_2 ... target_dir

The following creates a hard link to file foo called bar.

ln foo bar

The following creates a symbolic link to file foo called bar.

ln -s foo bar

• List of POSIX commands
• NTFS junction point

{{Reflist|30em}}

{{Wikibooks|Guide to Unix|Commands/File_System_Utilities#ln| File System Utilities - ln}}

• {{man|1|ln|die.net}}
• {{man|1|ln|FreeBSD}}
• {{man|1|ln|NetBSD}}
• {{man|1|ln|OpenBSD}}
• {{man|1|ln|Darwin}}

{{Unix commands}}

{{Core Utilities commands}}

Category:Standard Unix programs

Category:Unix SUS2008 utilities

Category:IBM i Qshell commands