In this example, you must rename the original command, although in other instances this isn't necessary because the command isn't exactly what people think it is in the first place ( java, for example, is rarely located in /usr/bin directly). For those terms, because they're environment variables and should be defined in /etc or $HOME/.profile.Ĭontinuing with the example scenario of an old binary called em being supplanted by the new variant nem, it's easy to create an alternative entry. For truly generic terms, like EDITOR and CC, the alternatives command is not considered an appropriate solution. Of course in the UNIX world, "generic" isn't always generic any more than "Kleenex" or "Xerox" is in the real world, so terms like java, (x)emacs(-nox), (n)vi(m), whois, and iptables are often some of the first to have alternatives defined for them. The alternatives command is most useful when managing "generic" application names.
Manually creating a symlink might seem tempting, but that's not resistant to updates from a package manager, nor is it centralized. The easy solution to this situation, and many other examples similar to it, is to designate the new nem binary as the preferred alternative to the em binary when the em command is used. You find a Unicode-enabled fork of em called nem, but you know that 99% of your users are used to em, have scripts that call em, and will continue to think of any replacement application as em no matter what you do. However, your userbase has made it clear to you recently that they can't survive any longer without emoji support in their terminal editors and em doesn't support Unicode. It's been the go-to editor for your userbase for years, many people have based workflows around it and some maintain highly customized configs for it. When to use the alternatives commandĪ simple and realistic example: you have a command on your system called em, which launches a simple text editor. Red Hat rewrote the command without Perl, and it's been propagated throughout Fedora-based distributions such as Red Hat and CentOS, as well as other distributions that look to Red Hat for the functional definition of the Linux Standard Base (LSB). Originally, this was a convenience utility, written in Perl, from the Debian Linux project, called update-alternatives. The alternatives command began its life as, interestingly, an alternative. Unless that is, you use the alternatives command. In theory, a Linux sysadmin can offer many system tools according to function rather than by the exact name of the executable, but that often requires a lot of symlinking and version tracking. In fact, even applications don't always care how something is achieved as long as all of its system calls are answered correctly. Linux system administration skills assessmentĪbstractions can be helpful to users because many users don't care how their computer achieves a task as long as it's on target.
A guide to installing applications on Linux.
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