From 19f4f86bfed21c5326ed2acebe1163f3a83e832b Mon Sep 17 00:00:00 2001 From: Daniel Baumann Date: Mon, 6 May 2024 04:25:50 +0200 Subject: Adding upstream version 241. Signed-off-by: Daniel Baumann --- man/sd-login.xml | 251 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 251 insertions(+) create mode 100644 man/sd-login.xml (limited to 'man/sd-login.xml') diff --git a/man/sd-login.xml b/man/sd-login.xml new file mode 100644 index 0000000..3743957 --- /dev/null +++ b/man/sd-login.xml @@ -0,0 +1,251 @@ + + + + + + + + + sd-login + systemd + + + + sd-login + 3 + + + + sd-login + APIs for + tracking logins + + + + + #include <systemd/sd-login.h> + + + + pkg-config --cflags --libs libsystemd + + + + + Description + + sd-login.h provides APIs to introspect + and monitor seat, login session and user status information on the + local system. + + Note that these APIs only allow purely passive access and + monitoring of seats, sessions and users. To actively make changes + to the seat configuration, terminate login sessions, or switch + session on a seat you need to utilize the D-Bus API of + systemd-logind, instead. + + These functions synchronously access data in + /proc, /sys/fs/cgroup + and /run. All of these are virtual file + systems, hence the runtime cost of the accesses is relatively + cheap. + + It is possible (and often a very good choice) to mix calls + to the synchronous interface of sd-login.h + with the asynchronous D-Bus interface of systemd-logind. However, + if this is done you need to think a bit about possible races since + the stream of events from D-Bus and from + sd-login.h interfaces such as the login + monitor are asynchronous and not ordered against each + other. + + If the functions return string arrays, these are generally + NULL terminated and need to be freed by the + caller with the libc + free3 + call after use, including the strings referenced therein. + Similarly, individual strings returned need to be freed, as + well. + + As a special exception, instead of an empty string array + NULL may be returned, which should be treated + equivalent to an empty string array. + + See + sd_pid_get_session3, + sd_uid_get_state3, + sd_session_is_active3, + sd_seat_get_active3, + sd_get_seats3, + sd_login_monitor_new3 + for more information about the functions + implemented. + + + + Definition of Terms + + + + seat + + A seat consists of all hardware devices assigned to a specific + workplace. It consists of at least one graphics device, and usually also includes + keyboard, mouse. It can also include video cameras, sound cards and more. Seats + are identified by seat names, which are strings (<= 255 characters), that start + with the four characters seat followed by at least one + character from the range [a-zA-Z0-9], _ and + -. They are suitable for use as file names. Seat names may or + may not be stable and may be reused if a seat becomes available again. + + + + + session + + A session is defined by the time a user is logged in until they + log out. A session is bound to one or no seats (the latter for 'virtual' ssh + logins). Multiple sessions can be attached to the same seat, but only one of them + can be active, the others are in the background. A session is identified by a + short string. + + + systemd1 + ensures that audit sessions are identical to systemd sessions, and uses the audit + session ID as session ID in systemd (if auditing is enabled). In general the + session identifier is a short string consisting only of [a-zA-Z0-9], + _ and -, suitable for use as a file name. + Session IDs are unique on the local machine and are + never reused as long as the machine is online. A user (the way we know it on UNIX) + corresponds to the person using a computer. A single user can have multiple + sessions open at the same time. A user is identified by a numeric user id (UID) or + a user name (a string). A multi-session system allows multiple user sessions on + the same seat at the same time. A multi-seat system allows multiple independent + seats that can be individually and simultaneously used by different users. + + + + + All hardware devices that are eligible to being assigned to a seat, are assigned + to one. A device can be assigned to only one seat at a time. If a device is not + assigned to any particular other seat it is implicitly assigned to the special default + seat called seat0. + + Note that hardware like printers, hard disks or network cards is generally not + assigned to a specific seat. They are available to all seats equally. (Well, with one + exception: USB sticks can be assigned to a seat.) + + seat0 always exists. + + + + udev Rules + + Assignment of hardware devices to seats is managed inside the udev database, via + settings on the devices: + + + + Tag seat + + When set, a device is eligible to be assigned to a seat. This tag + is set for graphics devices, mice, keyboards, video cards, sound cards and + more. Note that some devices like sound cards consist of multiple subdevices + (i.e. a PCM for input and another one for output). This tag will be set only for + the originating device, not for the individual subdevices. A UI for configuring + assignment of devices to seats should enumerate and subscribe to all devices with + this tag set and show them in the UI. Note that USB hubs can be assigned to a seat + as well, in which case all (current and future) devices plugged into it will also + be assigned to the same seat (unless they are explicitly assigned to another + seat). + + + + + Tag master-of-seat + + When set, this device is enough for a seat to be considered + existent. This tag is usually set for the framebuffer device of graphics cards. A + seat hence consists of an arbitrary number of devices marked with the + seat tag, but (at least) one of these devices needs to be + tagged with master-of-seat before the seat is actually + considered to be around. + + + + Property ID_SEAT + + This property specifies the name of the seat a specific device is + assigned to. If not set the device is assigned to seat0. Also, + to speed up enumeration of hardware belonging to a specific seat, the seat is also + set as tag on the device. I.e. if the property + ID_SEAT=seat-waldo is set for a device, the tag + seat-waldo will be set as well. Note that if a device is + assigned to seat0, it will usually not carry such a tag and you + need to enumerate all devices and check the ID_SEAT property + manually. Again, if a device is assigned to seat0 this is visible on the device in + two ways: with a property ID_SEAT=seat0 and with no property + ID_SEAT set for it at all. + + + + Property ID_AUTOSEAT + + When set to 1, this device automatically + generates a new and independent seat, which is named after the path of the + device. This is set for specialized USB hubs like the Plugable devices, which when + plugged in should create a hotplug seat without further configuration. + + + + + Property ID_FOR_SEAT + + When creating additional (manual) seats starting from a graphics + device this is a good choice to name the seat after. It is created from the path + of the device. This is useful in UIs for configuring seats: as soon as you create + a new seat from a graphics device, read this property and prefix it with + seat- and use it as name for the seat. + + + + A seat exists only and exclusively because a properly tagged device with the + right ID_SEAT property exists. Besides udev rules there is no + persistent data about seats stored on disk. + + Note that + systemd-logind8 + manages ACLs on a number of device classes, to allow user code to access the device + nodes attached to a seat as long as the user has an active session on it. This is + mostly transparent to applications. As mentioned above, for certain user software it + might be a good idea to watch whether they can access device nodes instead of thinking + about seats. + + + + + + See Also + + systemd1, + sd_pid_get_session3, + sd_uid_get_state3, + sd_session_is_active3, + sd_seat_get_active3, + sd_get_seats3, + sd_login_monitor_new3, + sd-daemon3, + pkg-config1 + + + + Multi-Seat on Linux + for an introduction to multi-seat support on Linux and the background for this set of APIs. + + + + -- cgit v1.2.3