Pastey's Blog

Pavlo Shkrabliuk, Software Developer

Project maintained by pastey Hosted on GitHub Pages — RSS — Theme by mattgraham

Journey HOME

This is the story about PATH, /usr/local/bin and a little bit about Homebrew.

At our project we use our own Git submodules system named system7. The story is actually not about s7, it could have happened to any other internal binary tool that we have.

s7 can be installed in two ways: using install scripts for Readdle internal use and using Homebrew. This means that there’s no single known path where the s7 binary may get installed.

s7 uses Git hooks to automate the work with subrepos as much as possible. Ideally, if the end user doesn’t have to rebind subrepos, they will not have to launch s7 by hand at all. For Git hooks to work properly, s7 must be visible from the context where a hook gets launched. There are two such contexts: CLI and GUI.

Historically, all Readdle internal tools are installed to “$HOME/bin”. I didn’t know any reasons for that and just followed the tradition. I’m a console person, so I tested s7 in terminal and everything worked smoothly.

From day one it became obvious that the majority of people prefer GUI tools to work with Git. My first reaction was,– “Then add “$HOME/bin” to the PATH?”. Turned out that adding something to the PATH for GUI apps is not an easy task at the modern macOS.

If you were curious, the default PATH for GUI apps looks like this /usr/bin:/bin:/usr/sbin:/sbin. Many apps add some stuff to the PATH once they launch, for example, SourceTree adds the paths to its custom git-lfs, Xcode adds SDK/bin, etc.

.bash_profile/.zshrc – don’t work for GUI apps*. I was sometimes fooled by my love to launch Xcode using xed, or SourceTree using stree. GUI apps started from Finder, Dock, Spotlight, or by launch services don’t consult shell profiles.

/etc/paths, /etc/paths.d/* – I had a vague hope this would work. No, it won’t. This one IS used by Terminal, but GUI doesn’t consult it.

launchctl setenv PATH VALUE – doesn’t work particularly for the PATH variable. Haven’t found it in the documentation, but my tests tell so. It works for custom variables, like MY_TESTlaunchctl setenv MY_TEST VALUE works, PATH – nah. Doesn’t work even if set from ~/Library/LaunchAgents/*.plist. (NOTE: Haven’t checked this, but people at Stack Overflow write that LaunchAgents-set variables don’t work for apps started by reopening the last open windows and for Preferences > Users & Groups > Login Items. Might be worth checking if we need a different environment variable someday).

The only way, my teammates found, that works is to run sudo launchctl config user path VALUE. I didn’t want users to trust me with superuser rights (even just for the installation) to work with s7 (considering that sudo <something> would be hidden in the guts of an install script/brew formula).

I turned my sight to the standard directories. /usr/local/bin in particular caught my attention. Xcode offers to install CLI tools to /usr/local/bin by default. As of that time, Homebrew used to install to /usr/local/bin by default. That, at least, offered a unification of the install path for our internal scripts and Homebrew. The default /etc/paths contains /usr/local/bin, so there was no need to modify the user’s PATH to make work from Terminal possible. The use of /usr/local/bin didn’t free me from the need to do something about PATH for GUI apps though.

Based on our experience, not all people keep an eye on internal utils updates (even though we send an email to the devlist on every update). People forget, they are busy, they don’t love CLI, and don’t want to bother. Depending on the utility that resulted in different issues. For example, a bug in the localization tool that had been fixed months ago would pop up in our project, ‘cause someone didn’t bother to update the necessary tool. To remove the human factor, we automated the necessary tools install and update process. We have the Run Phase in our Xcode project that updates our internal tools if necessary. I wanted to keep s7 up-to-date on every engineer’s machine. For Run Phase to be able to silently install updates, the installation directory must be writable for usual non-admin/non-sudo user. And /usr/local/bin had exactly such rights*.

Back to the original problem of GUI apps. s7 is “used” by GUI apps indirectly through Git hooks, so I came up with a solution: we settle s7 in the /usr/local/bin and hardcode /usr/local/bin/s7 in all s7 hooks. GUI apps won’t need to look up the PATH, for the day-to-day use in CLI there would be no need to modify the user’s PATH. Win-win! :tada:

Boy, was that the wrong path.

s7 was written in the time when few people had M1 Macs. We knew that /usr/local/bin didn’t exist on M1. But the reason was not clear. Once M1 emerged, Homebrew started using /opt/homebrew/ for ARM, and /usr/local/bin for Intel architecture. Well, that made sense for them 🤷‍♂️. But for us, with our hardcoded /usr/local/bin in Git hooks… Well, we build s7 on every user’s machine, so there was no need to separate architectures. By the time we got our first M1 Macs we didn’t want to change our decision to hardcode /usr/local/bin in Git hooks: that would mean migration, the need for a new PATH, or some dynamic search of s7. We didn’t want all that hassle, so we proclaimed that everyone who has M1 must do the following:

 sudo mkdir -p /usr/local/bin
 sudo chown "$USER" /usr/local/bin

That mimicked the rights on /usr/local/bin that we had on Intel machines.

Three years passed with the decision to live in /urs/local/bin.

Until I stumbled on this article.

It made me sweat.

With my own hands I made the team of about 30 engineers vulnerable to sudo spoofing.

And then the dam had broken… I have a Homebrew version of Git on my machine. To use it, I prepended /opt/homebrew/bin to my PATH. And what are the rights of /opt/homebrew/bin? owner = $USER, 775. Well, alright, I did this with my own hands again. I decided to check what the internet has to say about it. Sure enough, you will find the same answer,– “prepend. the. /opt/homebrew/bin. to. your. PATH.”. Even worse. Take a look at what /opt/homebrew/bin/brew shellenv does – it… prepends /opt/homebrew/bin to your PATH.

Sure enough, when I decided to use /usr/local/bin, this directory permissions were modified by Homebrew. Of course, I’m to blame too. After reading the article, every piece of puzzle I knew before just made the whole picture.

Our predecessors who chose “$HOME/bin” must have known something. We are moving back HOME.

My conclusions (that I’m afraid I might find wrong in future):

  1. if affected, restore “/usr/local/bin” rights to the factory settings. Well, it doesn’t exist by default :) So, if possible – remove it. If absolutely necessary: /usr/bin/sudo chown root:wheel /usr/local/bin and /usr/bin/sudo chmod o+rx /usr/local/bin
  2. always use full path for at least “/usr/bin/sudo”
  3. never prepend any user-writable directory to your PATH
  4. if you want to overwrite any /usr/bin utility (for example, git) – make a symlink in /usr/local/bin. See recomended permissions of this directory in (0). Just in case – you cannot overwrite anything in /usr/bin on a modern macOS
Written on September 8, 2023