On Wednesday 2021-06-02 09:40, Adam Majer wrote:

symlinks -- they only really allow a SINGLE choice to be preferred.

It so happens that any ordering of elements in a set implies that one is the first.

But, what happens when you run `node14` and then that program re-execs #!/usr/bin/node in a subprocess? The subprocess runs node16 and you are out of luck.

exec is a willfull boundary. (Just like /usr/libexec and /usr/bin.) Programs using these mechanisms _must not_ care about changes in architecture, language, memory layout, etc. nodejs's behavior sounds incredibly stupid.

I expect the same issue exists with ruby and python3 and other interpreters

python3 would hardly exec /usr/bin/python (v2). They're still sane.

The second issue that comes up is inability to actually manage preferences on a user level. Imagine you have all editors installed on a multi-user system. The user cannot specify their preferences bypass update-alternatives and resort to manual symlink hackery in ~/.bin or similar. [The plan is] moving the logic into a library. The /usr/bin/node would link to it and exec the preferred node version based on user preferences

Making /usr/bin/editor a program that painstakingly loads a ton of ELF libraries, parses config files is such a bad idea. Both export EDITOR=/usr/bin/joe alias editor='$EDITOR' export PAGER=/usr/bin/less or PATH="$HOME/bin:$PATH" ln -s /usr/bin/joe ~/bin/editor exec the "right" program, "right away" (after perhaps a search through PATH - it's still a _lot_ less syscalls).

On Wed, Jun 02, 2021 at 10:26:24AM +0200, Jan Engelhardt wrote:

On Wednesday 2021-06-02 09:40, Adam Majer wrote:

...

symlinks -- they only really allow a SINGLE choice to be preferred.

It so happens that any ordering of elements in a set implies that one is the first.

...

But, what happens when you run `node14` and then that program re-execs #!/usr/bin/node in a subprocess? The subprocess runs node16 and you are out of luck.

exec is a willfull boundary. (Just like /usr/libexec and /usr/bin.) Programs using these mechanisms _must not_ care about changes in architecture, language, memory layout, etc. nodejs's behavior sounds incredibly stupid.

Well, it needs to exec g++ and python3 - that's the GYP, build system. This in turns needs to find parameters, which is from node process and you end up with wrong one.

...

I expect the same issue exists with ruby and python3 and other interpreters

python3 would hardly exec /usr/bin/python (v2). They're still sane.

python3 exec python3, of course. But what happens if you have python3.8 and python3.10 installed and want your app to use python3.8? That app then starts a child process and you are in python3.10 then?

...

The second issue that comes up is inability to actually manage preferences on a user level. Imagine you have all editors installed on a multi-user system. The user cannot specify their preferences bypass update-alternatives and resort to manual symlink hackery in ~/.bin or similar. [The plan is] moving the logic into a library. The /usr/bin/node would link to it and exec the preferred node version based on user preferences

Making /usr/bin/editor a program that painstakingly loads a ton of ELF libraries, parses config files is such a bad idea. Both

export EDITOR=/usr/bin/joe alias editor='$EDITOR' export PAGER=/usr/bin/less

or

PATH="$HOME/bin:$PATH" ln -s /usr/bin/joe ~/bin/editor

exec the "right" program, "right away" (after perhaps a search through PATH - it's still a _lot_ less syscalls).

Not sure editor cares about syscall overhead. But yes, there is about 3 or 4 syscalls + the exec(). Starting actual interpreters like bash is a lot more overhead. - Adam

On Wed, Jun 02, 2021 at 10:50:11AM +0200, Jan Engelhardt wrote:

On Wednesday 2021-06-02 10:45, Ben Greiner wrote:

...

Am 02.06.21 um 10:26 schrieb Jan Engelhardt:

...

python3 would hardly exec /usr/bin/python (v2). They're still sane.

Many ignorant python scripts

Ignorant scripts are one thing. Ignorant node runtimes is another level.

Well, I kind of detect a bias? Here's a naive python example, f133:~ # cat worker.py #!/usr/bin/python3 import platform print(platform.python_version()) f133:~ # cat daemon.py #!/usr/bin/python3 import subprocess subprocess.Popen(['./worker.py']).wait() f133:~ # python3. python3.6 python3.6m python3.8 python3.9 f133:~ # python3.6 ./daemon.py 3.8.10 f133:~ # python3.6 ./worker.py 3.6.13 So, with node, if you did this experiment, and you started it with node10, you would get node10 in the worker irrespective what /usr/bin/node points to. Basically, once we allow multiple interpreters to be co-installed, they actually should run as expected. No? Saying the problem is "out of scope" tells me that something is abused for purposes that were not intended (looking at update-alternatives here). Anyway, this is an example of why pure symlinks are bad and actually result in confusion at runtime. - Adam

Am 02.06.21 um 14:52 schrieb Adam Majer:

On Wed, Jun 02, 2021 at 10:50:11AM +0200, Jan Engelhardt wrote:

...

On Wednesday 2021-06-02 10:45, Ben Greiner wrote:

...

Am 02.06.21 um 10:26 schrieb Jan Engelhardt:

...

python3 would hardly exec /usr/bin/python (v2). They're still sane.

Many ignorant python scripts

Ignorant scripts are one thing. Ignorant node runtimes is another level.

Well, I kind of detect a bias? Here's a naive python example,

f133:~ # cat worker.py #!/usr/bin/python3

import platform print(platform.python_version())

f133:~ # cat daemon.py #!/usr/bin/python3

import subprocess

subprocess.Popen(['./worker.py']).wait()

f133:~ # python3. python3.6 python3.6m python3.8 python3.9 f133:~ # python3.6 ./daemon.py 3.8.10 f133:~ # python3.6 ./worker.py 3.6.13

So, with node, if you did this experiment, and you started it with node10, you would get node10 in the worker irrespective what /usr/bin/node points to.

Basically, once we allow multiple interpreters to be co-installed, they actually should run as expected.

But how do you know what "is expected"? In the Python case we can only assume that PEP 394 is the de-facto standard: ---PEP 394--- - When reinvoking the interpreter from a Python script, querying sys.executable to avoid hardcoded assumptions regarding the interpreter location remains the preferred approach. ---PEP 394---

No? Saying the problem is "out of scope" tells me that something is abused for purposes that were not intended (looking at update-alternatives here).> Anyway, this is an example of why pure symlinks are bad and actually result in confusion at runtime.

Your example does not involve u-a at all. We don't put the python3 command under u-a control. We even go out of our way and fix the "ignorant scripts", who install wrong script interpreter lines and do something to the extent of replacing `subprocess.call("./worker.py")` or `subprocess.call("python", "./worker.py")` with `subprocess.call(sys.executable, "./worker.py")`. Am 02.06.21 um 10:46 schrieb Adam Majer:

python3 exec python3, of course. But what happens if you have python3.8 and python3.10 installed and want your app to use python3.8? That app then starts a child process and you are in python3.10 then?

If you know you want python3.8, then call python3.8. If the app depends on the same python version as it is called on the toplevel call, it MUST use `sys.executable`. `"/usr/bin/python3"` is always the current TW primary python3 flavor and all dependencies for the script calling it must be provided in that flavor. When Python setuptools installs "entrypoints" it takes care of the correct script interpreter automatically. In the case of multiple flavors, this is overwritten by `%python_clone -a %{buildroot}%{_bindir}/myentrypoint` creating the u-a symlinks and adjusting the script interpreter lines. Any python package, which installs commands into %{_bindir} must either be for the primary python3 flavor only or the handling of different flavors must be taken care of by u-a and adjusted script interpreter lines as described above. Apparently Node.js is more lenient on different flavors. But as you describe, this calls for problems with u-a. - Ben

Why are we using alternatives with Python anyway? Why not just use the swappable package strategy for `/usr/bin/python` and `/usr/bin/python3`?

Please read again. We are NOT using alternatives with the Python interpreter.

Hi , I noticed quite a bunch of submit requests to python packages such as https://build.opensuse.org/request/show/919833 (pip) and https://build.opensuse.org/request/show/919826 (ipython) For the sake of sanity. Please don't add Yet Another Way of Flavor Switching to the Python world on openSUSE distros, especially not in a way that makes the specfiles even more complicated than they already are. The python-rpm-macros support for update-alternatives works. It is not great, but it is the best thing we have so far. Am 02.06.21 um 09:40 schrieb Adam Majer:

Hi all,

[...]

The second issue that comes up is inability to actually manage preferences on a user level. Imagine you have all editors installed on a multi-user system. The user cannot specify their preferences and must bypass update-alternatives and resort to manual symlink hackery in ~/.bin or similar.

Python users are recommended to use virtual environments for such preferences on the user level. Adding yet another distribution specific way does not help to clear up the jungle. - Ben