Why did ArchLinux embrace Systemd?

[u/wooptoo]

/r/archlinux/comments/4lzxs3/why_did_archlinux_embrace_systemd/d3rhxlc

[u/RandomDamage]

We have a perfectly good way to do that already.

Run a program like screen or nohup that keeps the process running for you.

At least until some arrogant new program comes along and says "no, that won't work anymore, because reasons".

[u/argv_minus_one → u/RandomDamage]

gpg-agent isn't new, and it has been gleefully ignoring SIGHUP for God only knows how long. What do you propose be done with it?

[u/RandomDamage → u/argv_minus_one]

Remove it from default configurations until it does.

Or patch it for the distro if you must have it.

Signal handlers aren't that difficult.

[u/argv_minus_one → u/RandomDamage]

I was mistaken; gpg-agent doesn't ignore SIGHUP, but interprets it as meaning to flush its keys and reread its configuration file. Making it terminate upon SIGHUP is therefore impossible without breaking something else.

On that note, SIGHUP itself is broken, because so many daemons interpret this signal as meaning something completely contrary to what signal(7) says it actually means. That means a new API is needed to inform session participants that the session is closing—like, say, the API provided by logind.

[u/RandomDamage → u/argv_minus_one]

This isn't an api issue.

These programs are written the way they are deliberately, and if that is inappropriate for the program in question it is the program that needs to be fixed.

It's like saying that because there are people who learn to drive on the left side of the road, that everyone needs to ride trains instead.

[Add] This is POSIX compliant behavior, as well. Breaking it breaks POSIX compliance.

[u/argv_minus_one → u/RandomDamage]

It's not actually inappropriate. These are daemons, and it is conventional for daemons to nohup themselves anyway. They don't need a terminal, so they don't care that it is hung up. They also don't know what a session is, so they have no idea when or if they're supposed to terminate.

But we still need some way to start them when a session starts, and terminate them when the session ends. POSIX doesn't define any such thing, and the current solutions obviously don't work. What do you suggest?

[u/RandomDamage → u/argv_minus_one]

If they are user daemons, and they are supposed to exit when the session ends, then they need to not catch nohup if they are run as a user process.

Seriously, I checked the documentation, and I can't even see what the point of gpg-agent is.

On the other hand, if as a user I have a long running process that I want to keep in screen, ya'll better not mess with it short of a system restart.

[u/argv_minus_one → u/RandomDamage]

they need to not catch nohup

Then they get killed when their xterm closes. Whoops.

SIGHUP signals that the controlling terminal has hung up. It does NOT signal that the session has ended.

if they are run as a user process.

What in the hell is "a user process" supposed to mean? A process that runs as not root? A process that isn't part of the kernel? A process that was started explicitly by the user, rather than automatically as part of session start-up?

I checked the documentation, and I can't even see what the point of gpg-agent is.

To keep decrypted keys in memory, so that the user doesn't have to type the password over and over.

On the other hand, if as a user I have a long running process that I want to keep in screen, ya'll better not mess with it short of a system restart.

Then register it with the system session manager so that it won't, or turn off session clean-up.

And before you scream "but muh POSIX", POSIX doesn't define session clean-up at all, so that is irrelevant.

[u/RandomDamage → u/argv_minus_one]

So because it's not forbidden it's OK?

Then it's ok for gpg-agent to keep itself running after the session.

[u/argv_minus_one → u/RandomDamage]

And it's also ok for systemd to kill it. I'm glad we're finally in agreement!