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用ln命令建的连接：hard link 和symbolic link有什么区别？？
Commands Reference, Volume 3
ln Command
Purpose
Links files.
Syntax
To Link a File to a File
ln [ -f | -n ] [ -s ] SourceFile [ TargetFile ]
To Link a File or Files to a Directory
ln [ -f | -n ] [ -s ] SourceFile ... TargetDirectory
Description
The ln command links the file designated in the SourceFile parameter to the file
designated by the TargetFile parameter or to the same file name in another
directory specified by the TargetDirectory parameter. By default, the ln command
creates hard links. To use the ln command to create symbolic links, designate
the -s flag.
A symbolic link is an indirect pointer to a file; its directory entry contains
the name of the file to which it is linked. Symbolic links may span file systems and may refer to directories.
If you are linking a file to a new name, you can list only one file. If you are
linking to a directory, you can list more than one file.
The TargetFile parameter is optional. If you do not designate a target file, the
ln command creates a new file in your current directory. The new file inherits
the name of the file designated in the SourceFile parameter. See example 5.
Notes:
1. You cannot link files across file systems without using the -s flag.
2. If TargetDirectory is already a symbolic link to a directory, then the
ln command treats the existing target as a file. This means that a
command such as ln -fs somepath/lname symdir will not follow the
existing symbolic link of symdir, instead it will create a new symbolic
link from somepath/lname to symdir.
Flags
-f Causes the ln command to replace any destination paths that already exist. If
a destination path already exists and the -f flag is not specified, the ln
command writes a diagnostic message to standard error without creating a new
link and continues to link the remaining SourceFiles.
-n Specifies that if the link is an existing file, do not overwrite the contents
of the file. The -f flag overrides this flag. This is the default behaviour.
-s Causes the ln command to create symbolic links. A symbolic link contains the
name of the file to which it is linked. The referenced file is used when an open
operation is performed on the link. A stat call on a symbolic link returns the
linked-to file; an lstat call must be done to obtain information about the link.
The readlink call may be used to read the contents of a symbolic link. Symbolic
links can span file systems and refer to directories.
Note: Absolute path names must be used when specifying the SourceFile
parameter for the -s flag. If the absolute path name is not designated,
unexpected results may occur when the SourceFile and the TargetFile
parameters are located in different directories. The source file does not
need to exist before creating the symbolic link.
Exit Status
This command returns the following exit values:
0 All specified files were successfully linked.
>;0 An error occurred.
Examples
1. To create another link (alias) to a file, enter:
ln -f chap1 intro
This links chap1 to the new name, intro. If intro does not already exist,
the file name is created. If intro does exist, the file is replaced by a
link to chap1. Then both the chap1 and intro file names will refer to the
same file. Any changes made to one also appear in the other. If one file
name is deleted with the rm command, the file is not completely deleted
since it remains under the other name.
2. To link a file to the same name in another directory, enter:
ln index manual
This links index to the new name, manual/index.
Note: intro in example 1 is the name of a file; manual in example 2 is
a directory that already exists.
3. To link several files to names in another directory, enter:
ln chap2 jim/chap3 /home/manual
This links chap2 to the new name /home/manual/chap2 and jim/chap3 to
/home/manual/chap3.
4. To use the ln command with pattern-matching characters, enter:
ln manual/* .
This links all files in the manual directory into the current directory, .
(dot), giving them the same names they have in the manual directory.
Note: You must type a space between the asterisk and the period.
5. To create a symbolic link, enter:
ln -s /tmp/toc toc
This creates the symbolic link, toc, in the current directory. The toc file
points to the /tmp/toc file. If the /tmp/toc file exists, the cat toc
command lists its contents.
To achieve identical results without designating the TargetFile parameter,
enter:
ln -s /tmp/toc
Files
/usr/bin/ln Contains the ln command.
Related Information
The cp command, mv command, rm command.
The link subroutine, readlink subroutine, stat subroutine, symlink subroutine.
Directory Overview in AIX 5L Version 5.2 System User's Guide: Operating System
and Devices describes the structure and characteristics of directories in the
file system.
Files Overview in AIX 5L Version 5.2 System User's Guide: Operating System and
Devices describes files, file types, and how to name files.
Linking Files and Directories in AIX 5L Version 5.2 System User's Guide:
Operating System and Devices explains the concept of file linking.
Linking for Programmers in AIX 5L Version 5.2 General Programming Concepts:
Writing and Debugging Programs discusses links from a programming viewpoint. |
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发表于 2003-02-25 19:39
