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logind: don't start user@UID.service instance for background sessions

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We have had background session class for a long time (since commit
e2acb67baa), but so far the only difference in handling of background
sessions was logging, i.e. we log some messages with LOG_DEBUG for such
sessions.

Previously there were complains [1] about excessive logging for each
time cron session is started. We used to advise user to enable lingering
for users if they want to avoid these log messages. However, on servers
with a lot of users the extra processes that result from lingering just
adds too much overhead. Hence I think that our current handling of
background sessions is not ideal and we should make better use of this
attribute.

This commit introduces a change in default behavior of logind. Logind is
now not going to start user instance of systemd when background session
is created and that should address excessive logging problem for cron
where background class is used by default. When the same user actually
logs in normally then user instance will be started as previously.

Also note that PAM_TTY variable is now always set to some value for PAM
sessions started via PAMName= option. Otherwise we would categorize such
sessions as "background" and user manager won't be started.

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1825942
This commit is contained in:
Michal Sekletar 2022-05-27 21:11:37 +02:00 committed by Yu Watanabe
parent 948fce5118
commit e73bf3425c
7 changed files with 20 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
src/core/execute.c
View File

@ -1213,13 +1213,15 @@ static int setup_pam(
if (getttyname_malloc(STDIN_FILENO, &q) >= 0)
tty = strjoina("/dev/", q);
else
/* If everything else failed then let's just use value "systemd". This will cause that session
* isn't going to be marked as "background" and user manager will be started. */
tty = "systemd";
}
if (tty) {
pam_code = pam_set_item(handle, PAM_TTY, tty);
if (pam_code != PAM_SUCCESS)
goto fail;
}
pam_code = pam_set_item(handle, PAM_TTY, tty);
if (pam_code != PAM_SUCCESS)
goto fail;
STRV_FOREACH(nv, *env) {
pam_code = pam_putenv(handle, *nv);

2
src/login/logind-dbus.c
View File

@ -1305,7 +1305,7 @@ static int method_set_user_linger(sd_bus_message *message, void *userdata, sd_bu
return r;
if (manager_add_user_by_uid(m, uid, &u) >= 0)
user_start(u);
user_start(u, /* want_user_instance= */ true);
} else {
User *u;

6
src/login/logind-session.c
View File

@ -664,12 +664,12 @@ static int session_start_scope(Session *s, sd_bus_message *properties, sd_bus_er
description,
/* These two have StopWhenUnneeded= set, hence add a dep towards them */
STRV_MAKE(s->user->runtime_dir_service,
s->user->service),
s->class != SESSION_BACKGROUND ? s->user->service : NULL),
/* And order us after some more */
STRV_MAKE("systemd-logind.service",
"systemd-user-sessions.service",
s->user->runtime_dir_service,
s->user->service),
s->class != SESSION_BACKGROUND ? s->user->service : NULL),
user_record_home_directory(s->user->user_record),
properties,
error,
@ -700,7 +700,7 @@ int session_start(Session *s, sd_bus_message *properties, sd_bus_error *error) {
if (s->started)
return 0;
r = user_start(s->user);
r = user_start(s->user, /* want_user_instance= */ s->class != SESSION_BACKGROUND);
if (r < 0)
return r;

5
src/login/logind-user.c
View File

@ -442,7 +442,7 @@ static int user_update_slice(User *u) {
return 0;
}
int user_start(User *u) {
int user_start(User *u, bool want_user_instance) {
assert(u);
if (u->started && !u->stopping)
@ -465,7 +465,8 @@ int user_start(User *u) {
(void) user_update_slice(u);
/* Start user@UID.service */
user_start_service(u);
if (want_user_instance)
user_start_service(u);
if (!u->started) {
if (!dual_timestamp_is_set(&u->timestamp))

2
src/login/logind-user.h
View File

@ -57,7 +57,7 @@ DEFINE_TRIVIAL_CLEANUP_FUNC(User *, user_free);
bool user_may_gc(User *u, bool drop_not_started);
void user_add_to_gc_queue(User *u);
int user_start(User *u);
int user_start(User *u, bool need_user_instance);
int user_stop(User *u, bool force);
int user_finalize(User *u);
UserState user_get_state(User *u);

5
src/login/logind.c
View File

@ -1041,7 +1041,6 @@ static int manager_startup(Manager *m) {
int r;
Seat *seat;
Session *session;
User *user;
Button *button;
Inhibitor *inhibitor;
@ -1118,9 +1117,7 @@ static int manager_startup(Manager *m) {
HASHMAP_FOREACH(seat, m->seats)
(void) seat_start(seat);
HASHMAP_FOREACH(user, m->users)
(void) user_start(user);
/* Users are started by respective sessions */
HASHMAP_FOREACH(session, m->sessions)
(void) session_start(session, NULL, NULL);

5
src/login/pam_systemd.c
View File

@ -790,7 +790,10 @@ _public_ PAM_EXTERN int pam_sm_open_session(
* does the PAM session registration early for new connections, and registers a pty only
* much later (this is because it doesn't know yet if it needs one at all, as whether to
* register a pty or not is negotiated much later in the protocol). */
} else if (streq(tty, "systemd")) {
if (isempty(class))
class = "user";
tty = NULL;
} else
/* Chop off leading /dev prefix that some clients specify, but others do not. */
tty = skip_dev_prefix(tty);