O nás     Inzerce     KontaktSpolehlivé informace o IT již od roku 2011
Hledat
Nepřehlédněte: 2. kolo: Pozoruhodné IT produkty 2020
Správa dokumentů
Digitální transformace
Informační systémy
Hlavní rubriky: Informační systémy, Mobilní technologie, Datová centra, Sítě, IT bezpečnost, Software, Hardware, Zkušenosti a názory, Speciály

Pozoruhodné IT produkty 2020
E-knihy o IT zdarma
Odborné IT konference BusinessIT
Manuál Linux
[Linux manuál]

ln: vytvářet odkazy mezi soubory

Originální popis anglicky: ln - make links between files

Návod, kniha: General Commands Manual

STRUČNĚ

ln [options] source [dest]
 
ln [options] source... directory
 
POSIX options: [-f] [--]
 
GNU options (shortest form): [-bdfinsvF] [-S backup-suffix] [-V {numbered,existing,simple}] [--help] [--version] [--]

POPIS / INSTRUKCE

There are two concepts of `link' in Unix, usually called hard link and soft link. A hard link is just a name for a file. (And a file can have several names. It is deleted from disk only when the last name is removed. The number of names is given by ls(1). There is no such thing as an `original' name: all names have the same status. Usually, but not necessarily, all names of a file are found in the filesystem that also contains its data.)
A soft link (or symbolic link, or symlink) is an entirely different animal: it is a small special file that contains a pathname. Thus, soft links can point at files on different filesystems (possibly NFS mounted from different machines), and need not point to actually existing files. When accessed (with the open(2) or stat(2) system calls), a reference to a symlink is replaced by the operating system kernel with a reference to the file named by the path name. (However, with rm(1) and unlink(2) the link itself is removed, not the file it points to. There are special system calls lstat(2) and readlink(2) that read the status of a symlink and the filename it points to. For various other system calls there is some uncertainty and variation between operating systems as to whether the operation acts on the symlink itself, or on the file pointed to.)
ln makes links between files. By default, it makes hard links; with the -s option, it makes symbolic (or `soft') links.
If only one file is given, it links that file into the current directory, that is, creates a link to that file in the current directory, with name equal to (the last component of) the name of that file. (This is a GNU extension.) Otherwise, if the last argument names an existing directory, ln will create links to each mentioned source file in that directory, with a name equal to (the last component of) the name of that source file. (But see the description of the --no-dereference option below.) Otherwise, if only two files are given, it creates a link named dest to the file source. It is an error if the last argument is not a directory and more than two files are given.
By default, ln does not remove existing files or existing symbolic links. (Thus, it can be used for locking purposes: it will succeed only if dest did not exist already.) But it can be forced to do so with the option -f.
On existing implementations, if it is at all possible to make a hard link to a directory, this may be done by the superuser only. POSIX forbids the system call link(2) and the utility ln to make hard links to directories (but does not forbid hard links to cross filesystem boundaries).

POSIX OPTIONS

-f
Remove existing destination files.
--
Terminate option list.

GNU OPTIONS

-d, -F, --directory
Allow the super-user to make hard links to directories.
-f, --force
Remove existing destination files.
-i, --interactive
Prompt whether to remove existing destination files.
-n, --no-dereference
When given an explicit destination that is a symlink to a directory, treat that destination as if it were a normal file.
 
When the destination is an actual directory (not a symlink to one), there is no ambiguity. The link is created in that directory. But when the specified destination is a symlink to a directory, there are two ways to treat the user's request. ln can treat the destination just as it would a normal directory and create the link in it. On the other hand, the destination can be viewed as a non-directory - as the symlink itself. In that case, ln must delete or backup that symlink before creating the new link. The default is to treat a destination that is a symlink to a directory just like a directory.
-s, --symbolic
Make symbolic links instead of hard links. This option merely produces an error message on systems that do not support symbolic links.
-v, --verbose
Print the name of each file before linking it.

GNU BACKUP OPTIONS

The GNU versions of programs like cp, mv, ln, install and patch will make a backup of files about to be overwritten, changed or destroyed if that is desired. That backup files are desired is indicated by the -b option. How they should be named is specified by the -V option. In case the name of the backup file is given by the name of the file extended by a suffix, this suffix is specified by the -S option.
-b, --backup
Make backups of files that are about to be overwritten or removed.
-S SUFFIX, --suffix=SUFFIX
Append SUFFIX to each backup file made. If this option is not specified, the value of the SIMPLE_BACKUP_SUFFIX environment variable is used. And if SIMPLE_BACKUP_SUFFIX is not set, the default is `~'.
-V METHOD, --version-control=METHOD
Specify how backup files are named. The METHOD argument can be `numbered' (or `t'), `existing' (or `nil'), or `never' (or `simple'). If this option is not specified, the value of the VERSION_CONTROL environment variable is used. And if VERSION_CONTROL is not set, the default backup type is `existing'.
This option corresponds to the Emacs variable `version-control'. The valid METHODs are (unique abbreviations are accepted):
t, numbered
Always make numbered backups.
nil, existing
Make numbered backups of files that already have them, simple backups of the others.
never, simple
Always make simple backups.

GNU STANDARD OPTIONS

--help
Print a usage message on standard output and exit successfully.
--version
Print version information on standard output, then exit successfully.
--
Terminate option list.

ENVIRONMENT

The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have the usual meaning.

ODPOVÍDAJÍCÍ

POSIX 1003.2. However, POSIX 1003.2 (1996) does not discuss soft links. Soft links were introduced by BSD, and do not occur in System V release 3 (and older) systems.

SOUVISEJÍCÍ

ls(1), rm(1), link(2), lstat(2), open(2), readlink(2), stat(2), unlink(2)

NOTES

This page describes ln as found in the fileutils-4.0 package; other versions may differ slightly.
1998-11 GNU fileutils 4.0
©2011-2020 BusinessIT.cz, ISSN 1805-0522 | Názvy použité v textech mohou být ochrannými známkami příslušných vlastníků.
Provozovatel: Bispiral, s.r.o., kontakt: BusinessIT(at)Bispiral.com | Inzerce: Best Online Media, s.r.o., zuzana@online-media.cz
O vydavateli | Pravidla webu BusinessIT.cz a ochrana soukromí | pg(9286)