Note: This is an RHCSA 7 exam objective.
Hard and Soft Links
To create a hard link pointing to a existing file (here /path/file1) (both locations have to be in the same file system), type:
# ln /path1/file1 /path2/file2
Note1: It is not possible to create a hard link pointing to a directory.
Note2: In RHEL 7, only the owner of a file can create a hard link pointing to it. To get the RHEL 6 behavior back, add fs.protected_hardlinks = 0 in the /etc/sysctl.conf file and execute the command sysctl -p.
To create a soft link pointing to a existing file or directory (here /path/file1), type:
# ln -s /path1/file1 /path2/file2
Check the result:
# ls -i /path2/file2
Sander van Vugt provides a video about Understanding Links in the Linux File System (3min/2016).