From e73bf3425c0b5a6339388a3a459ce2bac497308b Mon Sep 17 00:00:00 2001 From: Michal Sekletar Date: Fri, 27 May 2022 21:11:37 +0200 Subject: [PATCH] logind: don't start user@UID.service instance for background sessions 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 --- src/core/execute.c | 12 +++++++----- src/login/logind-dbus.c | 2 +- src/login/logind-session.c | 6 +++--- src/login/logind-user.c | 5 +++-- src/login/logind-user.h | 2 +- src/login/logind.c | 5 +---- src/login/pam_systemd.c | 5 ++++- 7 files changed, 20 insertions(+), 17 deletions(-) diff --git a/src/core/execute.c b/src/core/execute.c index 05fc00ca1c..962edc1eee 100644 --- a/src/core/execute.c +++ b/src/core/execute.c @@ -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); diff --git a/src/login/logind-dbus.c b/src/login/logind-dbus.c index a426842bbb..e308e52af3 100644 --- a/src/login/logind-dbus.c +++ b/src/login/logind-dbus.c @@ -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; diff --git a/src/login/logind-session.c b/src/login/logind-session.c index 22bb4c3714..5808630503 100644 --- a/src/login/logind-session.c +++ b/src/login/logind-session.c @@ -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; diff --git a/src/login/logind-user.c b/src/login/logind-user.c index 3f1b8f610b..5f6cd590ce 100644 --- a/src/login/logind-user.c +++ b/src/login/logind-user.c @@ -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)) diff --git a/src/login/logind-user.h b/src/login/logind-user.h index 21b9f8f348..a20775ae70 100644 --- a/src/login/logind-user.h +++ b/src/login/logind-user.h @@ -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); diff --git a/src/login/logind.c b/src/login/logind.c index d14a17274b..2fdcd1d55e 100644 --- a/src/login/logind.c +++ b/src/login/logind.c @@ -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); diff --git a/src/login/pam_systemd.c b/src/login/pam_systemd.c index cb6a6fb514..677a014078 100644 --- a/src/login/pam_systemd.c +++ b/src/login/pam_systemd.c @@ -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);