In Linux, we can make a variable unchangeable by using the readonly builtin command in the Bash shell. This command can be used to mark a shell variable as read-only, which means that it cannot be modified or unset.  Below is an example of how to use the readonly command:  $ x=10
$ readonly x
$ x=20 bash: x: readonly variable  In the example above, the variable x is first set to the value 10. The readonly command is then used to mark x as a read-only variable. Finally, an attempt is made to change the value of x to 20, but this results in an error because x is a read-only variable.  It is important to note that the readonly command only works within the Bash shell and does not affect the variables in other processes or programs. It is also specific to the shell in which it is used, so a variable marked as read-only in one shell may not be read-only in another shell.