Create links between files
The ln command is used to create links between files. There are two types of links: hard links and symbolic links (also known as soft links). By default, ln creates hard links. To create a symbolic link, the -s option must be used.
Note: A symbolic link is not an independent file; many of its attributes depend on the source file. Therefore, setting access permissions for a symbolic link file is generally meaningless.
ln [options]... [-T] target link_name (1st format)
ln [options]... target (2nd format)
ln [options]... target... directory (3rd format)
ln [options]... -t directory target... (4th format)
--backup[=CONTROL] # Create a backup for each existing destination file
-b # Like --backup but does not accept an argument
-d, -F, --directory # Allow the superuser to attempt to hard link directories
-f, --force # Remove existing destination files
-i, --interactive # Prompt whether to remove destinations
-L, --logical # Dereference targets that are symbolic links
-n, --no-dereference # Treat LINK_NAME as a normal file if it is a symbolic link to a directory
-P, --physical # Make hard links directly to symbolic links
-r, --relative # Create symbolic links relative to link location
-s, --symbolic # Make symbolic links instead of hard links
-S, --suffix=SUFFIX # Override the usual backup suffix (default is ~)
-t, --target-directory=DIRECTORY # Specify the DIRECTORY in which to create the links
-T, --no-target-directory # Treat LINK_NAME as a normal file always
-v, --verbose # Print name of each linked file
--help # Display this help and exit
--version # Output version information and exit
-s, the source can be a file or a directory. When creating a hard link, the source must be a file.# CONTROL argument for --backup:
none, off # Never make backups (even if --backup is given)
numbered, t # Make numbered backups
existing, nil # Numbered if numbered backups exist, simple otherwise
simple, never # Always make simple backups
Link the file m2.c in /usr/mengqc/mub1 to a2.c in /usr/liu:
cd /usr/mengqc
ln mub1/m2.c /usr/liu/a2.c
Before execution, a2.c does not exist in /usr/liu. After execution, a2.c appears as a link to m2.c (physically they are the same file). You can see the link count increase using ls -l.
Creating a symbolic link
Create a symbolic link abc in /usr/liu pointing to the directory /usr/mengqc/mub1:
ln -s /usr/mengqc/mub1 /usr/liu/abc
Creating a hard link
Create a hard link ln2022 for the file log2022.log. Both files will share the same attributes and data:
ln log2022.log ln2022
Output:
[root@localhost test]# ll
lrwxrwxrwx 1 root root 11 12-07 16:01 link2013 -> log2022.log
-rw-r--r-- 1 root bin 61 11-13 06:03 log2022.log
[root@localhost test]# ln log2022.log ln2022
[root@localhost test]# ll
lrwxrwxrwx 1 root root 11 12-07 16:01 link2013 -> log2022.log
-rw-r--r-- 2 root bin 61 11-13 06:03 ln2022
-rw-r--r-- 2 root bin 61 11-13 06:03 log2022.log
Linux allows multiple names for a single file, a feature known as linking. Linked files can reside in the same directory but must have different names, avoiding redundant backups on the disk. They can also have the same name if placed in different directories; modifying one will affect all others since they point to the same data. Different access permissions can be assigned to different links to control sharing and security.
There are two types of links: hard links and symbolic links.
The ln command creates a synchronous link in another location. When the same file is needed in different directories, there's no need to store multiple copies; just store the file once and use ln to link to it elsewhere, saving disk space.
⚠️ The
lncommand maintains synchronicity across all linked files; changes made to one will be reflected in all others.
Creating a hard link adds a directory entry in the same or another directory pointing to the same file data.
ls -ailR
.:
total 16
922730 drwxr-xr-x 4 root root 4096 Jun 17 11:18 .
393217 drwxrwxrwt. 9 root root 4096 Jun 17 11:19 ..
922733 drwxr-xr-x 2 root root 4096 Jun 17 11:18 liu
922731 -rw-r--r-- 3 root root 0 Jun 17 11:18 m2.c
922732 drwxr-xr-x 2 root root 4096 Jun 17 11:18 mub1
./liu:
total 8
922733 drwxr-xr-x 2 root root 4096 Jun 17 11:18 .
922730 drwxr-xr-x 4 root root 4096 Jun 17 11:18 ..
922731 -rw-r--r-- 3 root root 0 Jun 17 11:18 m2.c
./mub1:
total 8
922732 drwxr-xr-x 2 root root 4096 Jun 17 11:18 .
922730 drwxr-xr-x 4 root root 4096 Jun 17 11:18 ..
922731 -rw-r--r-- 3 root root 0 Jun 17 11:18 m2.c
After creating hard links, the inode number of the existing file is shared by multiple directory entries. The link count is shown in the second column of the ls -l output.
By default, ln creates hard links. ln increases the link count, while rm decreases it. A file is not physically deleted from the file system until its link count reaches zero.
Restrictions on hard links:
A symbolic link links a path name to a file. It is a special type of file that contains the path name of another file. When commands read or write to a symbolic link, the system follows the link to access the actual file.
$ ls -il
total 0
922736 lrwxrwxrwx 1 root root 5 Jun 17 11:27 abc -> a.txt
922735 -rw-r--r-- 1 root root 0 Jun 17 11:27 a.txt
Unlike hard links, a symbolic link is a new file with its own inode. It does not have the restrictions of hard links: it can point to directories and cross file systems.
When creating a symbolic link with ln -s, it is recommended to use absolute paths for the source to ensure the link works regardless of the current working directory.
Key characteristics of symbolic links:
l as the first character of the permissions string.ls -l shows the link target with an arrow (e.g., abc -> a.txt).