1. Overview
In this tutorial, we’ll learn when and how to use /opt in Linux. We’ll start with its definition. Then, we’ll cover how it is different from /usr/local.
2. Introduction
Let’s see the Linux directory structure executing ls at the root level:
bin dev lib opt usr
boot etc lib64 proc srv
cdrom home lost+found root config
media run sys core mnt
sbin tmp var
What we see in the output are standard Linux root-level directories. What each directory and its subdirectories should contain in a Linux system is defined in the FHS (Filesystem Hierarchy Standard).
The FHS defines /opt as “reserved for the installation of add-on application software packages.” In this context, “add-on” means software that is not part of the system; for example, any external or third-party software. This convention has its roots in the old UNIX systems built by vendors like AT&T, Sun, and DEC.
3. Using /opt
Let’s take an internal application developed in a company, CompanyApplication, as an example.
If we don’t package it using standard tools, such as dpkg or rpm, we’ll most likely put all of the files related to CompanyApplication in a single directory. So we’ll have the binaries, libraries, and configuration together. They won’t be separated into different locations as a traditional UNIX system would have them.
Let’s say we want to deploy our application on a server. In this case, we can just copy the directory of our application in the /opt/CompanyApplication directory.
When needed, we can execute it directly from there. Therefore when using /opt, installing our application is as simple as copying, extracting a TAR, or unzipping. And when we don’t need the application anymore, we can remove it simply by removing the directory under /opt.
As a side note, we can also prefer using a /opt/Company/CompanyApplication directory structure. In this case, we should use a LANANA registered company/provider name.
Deploying software by copying a directory is unconventional for a traditional UNIX system. Normally a UNIX application would have its libraries, binaries, and other files in separate directories, such as /usr/local/bin, and /usr/local/lib.
Let’s see the difference between the UNIX way of deploying software and /opt.
4. /usr/local vs /opt
The FHS defines /usr/local as “For use by the system administrator when installing software locally”. This may be confusing, as this description is very similar to /opt. On the other hand, there’s an important difference.
The hierarchy under /usr/local should mimic the hierarchy under /usr. This means we should place all the application binaries in /usr/local/bin, and all the libraries in /usr/local/lib, and so on. As a result, we’ll place them along with the files of the other applications.
Therefore, we can’t have a single directory for each application when deploying into /usr/local. Instead, we organize them in the more conventional UNIX style that divides application files to separate directories.
Some of the reasons for this traditional approach are:
- When we have all the binaries in /usr/local/bin, we can just add this single directory to our $PATH, so we can execute all of the binaries we installed without additional configuration.
- When all installed libraries are in /usr/local/lib, multiple binaries can share the same library, so we avoid having multiple copies of the same library on our system.
On the other hand, /opt doesn’t have these directory structure restrictions. As long as the applications in /opt are in separate directories, they can have custom directory structures inside these directories. They can have duplicate copies of libraries already installed in the system, and they may require additional $PATH configuration to execute from the terminal.
4.1. Use Cases
Let’s see some possible scenarios for /opt and /usr/local:
- Our application is a single binary, then we’ll copy or link it to /usr/local
- We want to use an alternative of an existing system program build from source using make. In this case, we’ll install it under /usr/local
- We’re going to deploy an application, and by design, all of its files are in the same directory. Then, we’ll deploy it by copying this directory into the /opt/myapp directory
5. Conclusion
In this tutorial we’ve seen how /opt is used, and its difference from other deployment methods such as /usr/local.