Comment by cyberax
2 days ago
They're already reported. And ignored. Have you _seen_ the systemd issue backlog?
The iSCSI loop issue: https://github.com/systemd/systemd/issues/34164 It keeps popping up again and again and is summarily ignored.
The remote FS detection also came up multiple times, and the maintainers don't care.
> and the maintainers don't care.
I'm not sure that's fair. I think better proof of this would be a rejected PR rather than a neglected bug report.
This is Linux, after all. Problems found with specific hardware are almost always solved by people with that hardware, not the maintainers, who are usually busy with the 99%.
The problem here is more fundamental.
Lennart refused to make all the /etc/fstab options available in regular mount units. And yes, there was an issue, no I'm too tired to look for it. The wording was pretty much: "Give up, and gtfo, this is not going to happen. Just because."
I'm convinced that systemd can't be fixed by its current team of maintainers. They are just... untidy.
I don't know about you, but if I end up writing low-level code that _needs_ to know whether the mounted file system is "remote", I won't do that by comparing against a hard-coded list of filesystems inside PID0. Or by using wild heuristics ("if it's on a block device, then it's local").
I would put these heuristics in a helper tool that populates the default values for mount units. Then allow users to override them as needed. With a separate inspector tool to flag possible loops.
This is one example of a more general complaint about systemd and related projects: they force policy, rather than simply providing mechanisms.
I recently did a deep dive on my laptop because I was curious about an oddity - the /sys file to change my screen backlight (aside, why /sys and not /dev anyway?) was writable only by root - yet any desktop shell running as my user had no problem reacting to brightness hotkeys. I wondered, how did this privilege escalation work? Where was the policy, and what property of my user account granted it the right to do this?
It turns out the answer is that the desktop shells are firing off a dbus request to org.freedesktop.login1, which is caught by systemd-logind - or elogind in my case, since I do not care for systemd. A login manager seemed an odd place for screen brightness privilege escalation, but hey if it works whatever - it seemed like logind functioned as a sort of miscellaneous grab bag of vaguely console-related stuff. Generally speaking, it consults polkit rules to determine whether a user is allowed to do a thing.
Not screen brightness, though. No polkit rules. Nothing in pkaction. logind was unilaterally consenting to change the brightness on my behalf. And on what grounds? It wasn't documented anywhere so I had to check the source code, where I found a slew of hardcoded criteria that mostly revolve around physical presence at the machine. Want to change screen brightness over ssh? Oh but why would you ever want to do that? Hope you have root access, you weirdo.
I removed elogind. A few odds and ends broke. But nobody tells me what to do with my machine.
> I think better proof of this would be a rejected PR rather than a neglected bug report.
I understand the sentiment you're expressing here, and it's often a reasonable one.
However, when every sharp edge case I've encountered with SystemD (both professionally and personally) ends either in a open Github Issue whose discussion from the project maintainers ends up being "Wow. That's tricky. I'm not sure whether or not that behavior is correct. Maybe we should do something about this or document this so other folks know about it." (and then nothing happens, not even the documentation) or a closed Github Issue with "Sorry, your usecase is <strike>inconvenient to implement</strike> unsupported. E_NOTABUG", expecting PRs is expecting way too much.
I've long been in the habit of reading accounts like yours, understanding the truth and wisdom that's being expressed, then noping the fuck out of the tech/product/situation in question. It has saved me a lot of trouble over the years. Even as others are completely mystified. Some people just like abuse, I guess.
"Sweet dreams are made of this..."
OK, think it through...
How do we determine that a specific instance of a filesystem mount is "remote", or even requires a "network"? Consider that the network endpoint might be localhost, a netlink/unix/other socket, or, say, an IP address of the virtual host (practically guaranteed to be there and not truly "remote").
systemd has .mount units which are way more configurable than /etc/fstab lines, so they'd let you, as the administrator, describe the network dependency for that specific instance.
But what if all we have is the filesystem type (e.g. if someone used mount or /etc/fstab)?
Linux doesn't tell us that the filesystem type is a network filesystem. Linux doesn't tell us that the specific mount request for that filesystem type will depend on the "network". Linux doesn't tell us that the specific mount request for that filesystem type will require true network connectivity beyond the machine itself.
So, before/without investing in a long-winded and potentially controversial improvement to Linux, we're stuck with heuristics. And systemd's chosen heuristic is pretty reasonable - match against a list of filesystem types that probably require network connectivity.
If you think that's stupid, how would you solve it?
> How do we determine that a specific instance of a filesystem mount is "remote", or even requires a "network"?
Like systemd authors do! Hard-code the list of them in the kernel, including support for fuse and sshfs. Everything else is pure blasphemy and should be avoided.
Me? I'd have an explicit setting in the mount unit file, with defaults inferred from the device type. I would also make sure to not just randomly add landmines, like systemd-update-done.service. It has an unusual dependency requirements, it runs before the network filesystems but after the local filesystems.
I bet you didn't know about it? It's a service that runs _once_ after a system update. So the effect is that your system _sometimes_ fails to boot.
> systemd has .mount units which are way more configurable than /etc/fstab lines
It's literally the inverse. As in, /etc/fstab has _more_ options than native mount units. No, I'm not joking.
Look at this man page: https://www.freedesktop.org/software/systemd/man/latest/syst... The options with "x-systemd." prefix are available for fstab.
Look for the string: "Note that this option can only be used in /etc/fstab, and will be ignored when part of the Options= setting in a unit file."
Sounds like your admin, distro, or the systemd team could pay some attention to systemd-update-done.service
The "can only be used in /etc/fstab" systemd settings are essentially workarounds to do those things via fstab (and workaround fstab related issues) rather than depend on other systemd facilities (c.f. systemd-gpt-auto-generator). From a "what can you do in /etc/fstab without knowing systemd is working behind the scenes" point of view, then yes, systemd units are vastly more configurable.
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> How do we determine that a specific instance of a filesystem mount is "remote", or even requires a "network"?
The '_netdev' option works a treat on sane systems. From mount(8):
It should work on SystemD and is documented to in systemd.mount
but -surprise surprise- it doesn't reliably work as documented because SystemD is full of accidental complexity.
Sure, and systemd would translate that directly into a dependency on network startup, which is precisely equivalent to the approach I mentioned that depends on operator knowledge. It's configuration, not "just works" inference.
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