Create links between files

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Manage links between files

hard/soft link

Create multiple names pointing to the same file.

Create hard link

Every file starts with a hard link, from its initial name to the file system's data. When a new hard link to a file is created, another name pointing to the same data is also created. The new hard link has the same effect as the original file name. Once created, the new hard link is identical to the file's original name.

[root@servera ~]# pwd
/root
[root@servera ~]# touch newfile.txt
[root@servera ~]# ls -l  newfile.txt
-rw-r--r--. 1 root root 0 Jul 16 04:53 newfile.txt

newfile.txtThe number of links is 1, absolute address/root/newfile.txt

Use the ln command to create a new hard link to an existing file. At least two parameters are required, namely the path to the existing file and the path to the hard link to be created.

Create a hard link to the existing file newfile.txt in the /tmp directory

[root@servera ~]# ls -l newfile.txt /tmp/newfile-link2.txt
-rw-r--r--. 2 root root 0 Jul 16 04:53 newfile.txt
-rw-r--r--. 2 root root 0 Jul 16 04:53 /tmp/newfile-link2.txt

If you want to know whether two files are hard links to each other, use ls -i to list the inode numbers of the files. If the files are on the same system and have an index numbering system, then the two files are hard links pointing to the same data.


[root@servera ~]# ls -il newfile.txt /tmp/newfile-link2.txt
33579695 -rw-r--r--. 2 root root 0 Jul 16 04:53 newfile.txt
33579695 -rw-r--r--. 2 root root 0 Jul 16 04:53 /tmp/newfile-link2.txt

Even if the original file is deleted, the file content will still be available as long as at least one hard link exists. Only deleting the last hard link will remove the data from storage.


[root@servera ~]# rm -f newfile.txt
[root@servera ~]# ls -l /tmp/newfile-link2.txt
-rw-r--r--. 1 root root 6 Jul 16 05:03 /tmp/newfile-link2.txt
[root@servera ~]# cat /tmp/newfile-link2.txt
Hello

Hard link limitations

Only for regular files, you cannot use ln to create hard links to directories or special files
Hard links can only be used when both files are on the same file system.

List directories located on different file systems


[root@servera ~]# df
Filesystem            1K-blocks    Used Available Use% Mounted on
devtmpfs                 874504       0    874504   0% /dev
tmpfs                    894592       0    894592   0% /dev/shm
tmpfs                    894592    8900    885692   1% /run
tmpfs                    894592       0    894592   0% /sys/fs/cgroup
/dev/mapper/rhel-root  17811456 1884916  15926540  11% /
/dev/nvme0n1p1          1038336  225396    812940  22% /boot
tmpfs                    178916       0    178916   0% /run/user/0

The files of two different Mounted On directories and their subdirectories are on different file systems.

Create soft link

Created by ln -s, soft links are not regular files, but special files that point to existing files or directories.

Can link two files on different file systems
Can point to a directory or special file, not limited to regular files

To /tmp/newfile-link2.txtcreate a new soft link


[root@servera ~]# ln -s /tmp/newfile-link2.txt /tmp/newfile-symlink.txt
[root@servera ~]# ls -l /tmp/newfile-link2.txt  /tmp/newfile-symlink.txt
-rw-r--r--. 1 root root  6 Jul 16 05:03 /tmp/newfile-link2.txt
lrwxrwxrwx. 1 root root 22 Jul 16 05:17 /tmp/newfile-symlink.txt -> /tmp/newfile-link2.txt
[root@servera ~]# cat /tmp/newfile-symlink.txt
Hello

When the original regular file is deleted, the soft link still points to the file, but the target disappears. Soft links pointing to missing files become "dangling soft links"


[root@servera ~]# rm -rf /tmp/newfile-link2.txt
[root@servera ~]# ls -l  /tmp/newfile-symlink.txt
lrwxrwxrwx. 1 root root 22 Jul 16 05:17 /tmp/newfile-symlink.txt -> /tmp/newfile-link2.txt
[root@servera ~]# cat /tmp/newfile-symlink.txt
cat: /tmp/newfile-symlink.txt: No such file or directory

Soft links can point to directories. Plays the same role as a directory. Changing to a soft link via cd will change the current working directory into the linked directory. Some tools can track the fact that the current working directory was reached using soft links. For example, cd will update the current working directory with the name of the soft link. -P updates to actual directory name.

Create a soft link pointing to the /etc directory


[root@servera ~]# ln -s /etc /root/configfiles
[root@servera ~]# cd /root/configfiles/

[root@servera configfiles]# cd -P /root/configfiles/
[root@servera etc]# pwd
/etc
[root@servera etc]# cd /root/configfiles/
[root@servera configfiles]# pwd
/root/configfiles