On 21/01/26 02:06PM, Pekka Paalanen wrote: > On Tue, 26 Jan 2021 01:43:43 -0800 > Kian Kasad <kian@xxxxxxxxx> wrote: > > > Hi all, > > > > After reading the documentation on logind and multi-seat (specifically > > sd-login(3) and "Multi-Seat on Linux"), I still have some questions. > > > > First of all, what exactly is multi-seat? Does it just mean allowing > > multiple sessions to be running at once, like for multiple users to be > > logged into the same desktop, even though only one will be in use at a > > time? > > > > Second, why is logind needed for this? Is it not possible to do without > > logind? I've run Xorg perfectly fine on systems without logind/systemd, > > so is logind only needed for multiple sessions at once? Is it just to > > handle the graphical device(s)? > > > > Third, is multi-seat possible at all without logind? > > > > Most of these questions arose because my main OS, Artix Linux, requires > > logind (in the form of elogind) for Xorg, but I know that Xorg runs just > > fine on Alpine Linux, which does not use logind at all. > > Hi, > > I've heard good words of https://sr.ht/~kennylevinsen/seatd/ although I > haven't tried to use it myself. One more way to handle multiseat - to > bind them all. I'll write this one down. I'm not looking for alternatives currently, I was just confused about the purpose. > IOW, there are many ways to achieve coordination between multiple > sessions and one or multiple physical seats, like the Linux virtual > terminal system that requires root permissions, ioctl and signal magic > to let things cooperate (and if things do not explicitly cooperate > correctly, it fails horribly) and does not support multiseat. But if > you want your program to not need root permissions, have a graceful > failure if it crashes, not accidentally hijack the seat by mistake, or > just support multiseat, you kind of need to have a system daemon > orchestrating things. > > Logind is one of those possible system daemons. It tells your program > when it is active. It grants access to graphics and input devices > without your program needing root permissions. It also takes graphics > and input devices away from your program when deactivated, so you can't > e.g. spy on other programs' input. It takes care of the arcane magic of > setting up the VT and tty and restoring them. And more. > > "Your program" here is Xorg, for instance. Or one of the Wayland > compositors. Thank you! This is exactly the explanation I was looking for. I didn't get why a daemon was needed if programs (like Xorg) can handle the devices on their own, but now I see it's to allow multiple Xorg/Wayland sessions to run, all without needing SUID. -- Kian Kasad PGP 0x1715EEAA14DAEC14
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