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switch-to-configuration-ng: rework user-unit migration candidate selection

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The previous "FragmentPath not under /etc" deny-list swept up units that
were never managed by a per-user manager (e.g. dbus-broker, whose
FragmentPath systemd reports under /run/current-system/sw/share via
systemd.packages) and missed nothing it should have caught, but for the
wrong reason.

Make the intent explicit. A unit is a migration candidate iff it is
active, the new generation defines it in /etc/systemd/user, and either
  * its FragmentPath is under $XDG_CONFIG_HOME/systemd/user (the
    home-manager case; ~/.config shadows /etc, so we must wait for
    sd-switch to remove the copy), or
  * its FragmentPath is anywhere else outside /etc and the previous
    generation did not have it in /etc (package-shipped units found via
    $XDG_DATA_HOME / $XDG_DATA_DIRS, e.g. ~/.nix-profile/share; /etc
    outranks these so it wins on daemon-reload).

The "previous generation did not have it" guard keeps units that have
always been in /etc, but whose FragmentPath systemd reports elsewhere, out
of the candidate set, and the existing now_etc check verifies /etc
actually won before acting. Compare FragmentPath by parent directory
instead of string prefix while here.

Covered by a new switch-test case that seeds a unit in
~/.local/share/systemd/user.
This commit is contained in:
r-vdp
2026-05-22 12:42:19 +02:00
parent 76c8d45099
commit 6ced06a1b3
2 changed files with 108 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files
nixos/tests/switch-test.nix
+39
View File
@@ -826,6 +826,15 @@ in
RemainAfterExit=true
ExecStart=${pkgs.runtimeShell} -c 'echo home > %t/migrated-owner'
'';
# Unit file placed in ~/.local/share/systemd/user (lower priority than
# /etc) to simulate a package-shipped unit.
dataMigratedUnit = pkgs.writeText "migrated.service" ''
[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=${pkgs.runtimeShell} -c 'echo data > %t/migrated-owner'
'';
in
# python
''
@@ -1857,6 +1866,36 @@ in
out = machine.succeed(f"sudo -u usertest {user_env} cat /run/user/1001/migrated-owner")
assert_contains(out, "home")
# Migration from a lower-priority search-path entry ($XDG_DATA_HOME
# here, standing in for ~/.nix-profile/share etc.). /etc outranks
# these, so pass 2 must restart onto the /etc definition.
switch_to_specialisation("${machine}", "")
machine.fail(f"sudo -u usertest {user_env} systemctl --user is-active migrated.service")
machine.succeed(
"sudo -u usertest mkdir -p ~usertest/.local/share/systemd/user",
"sudo -u usertest cp ${dataMigratedUnit} ~usertest/.local/share/systemd/user/migrated.service",
)
user_systemctl("daemon-reload")
user_systemctl("start migrated.service")
user_systemctl("is-active migrated.service")
out = machine.succeed(f"sudo -u usertest {user_env} cat /run/user/1001/migrated-owner")
assert_contains(out, "data")
out = user_systemctl("show -p FragmentPath migrated.service")
assert_contains(out, "/.local/share/systemd/user/migrated.service")
out = switch_to_specialisation("${machine}", "userServiceMigratedShadowed")
assert_contains(out, "restarting (post-activation) the following user units: migrated.service")
user_systemctl("is-active migrated.service")
out = user_systemctl("show -p FragmentPath migrated.service")
assert_contains(out, "/etc/systemd/user/migrated.service")
out = machine.succeed(f"sudo -u usertest {user_env} cat /run/user/1001/migrated-owner")
assert_contains(out, "nixos")
# Switching again must NOT touch it: /etc already had it, so it is
# not a candidate even though the lower-priority copy is still there.
out = switch_to_specialisation("${machine}", "userServiceMigratedShadowed")
assert_lacks(out, "migrated.service")
machine.succeed("sudo -u usertest rm -rf ~usertest/.local/share/systemd")
user_systemctl("daemon-reload")
# Units that remain shadowed by ~/.config must be left alone in both
# passes even though /etc now also defines them.
switch_to_specialisation("${machine}", "")
pkgs/by-name/sw/switch-to-configuration-ng/src/main.rs
+69 -16
View File
@@ -1395,26 +1395,79 @@ fn do_user_switch(parent_exe: String) -> anyhow::Result<()> {
let current_active_units = get_active_units(&systemd)?;
let old_unit_dir = old_toplevel.join(scope.etc_dir());
let new_unit_dir = toplevel.join(scope.etc_dir());
let fragment_prefix = scope
.current_dir()
.to_str()
.expect("scope dir is valid UTF-8");
let fragment_dir = scope.current_dir();
// Units that are currently running from a non-/etc location (typically
// ~/.config/systemd/user, i.e. home-manager) but that the new NixOS
// configuration also defines. Pass 1 will skip these because of the
// FragmentPath filter; if the per-user activation (sd-switch) later drops
// its copy, we need a second pass to bring the NixOS-owned definition up.
// Determine $XDG_CONFIG_HOME/systemd/user from the user manager's own
// environment (we are spawned with env_clear()).
let user_config_unit_dir: Option<PathBuf> = match systemd.environment() {
Err(err) => {
log::debug!("Failed to read user manager environment: {err}");
None
}
Ok(env) => {
let lookup = |key: &str| {
env.iter().find_map(|kv| {
kv.strip_prefix(key)
.and_then(|rest| rest.strip_prefix('='))
.filter(|v| Path::new(v).is_absolute())
.map(PathBuf::from)
})
};
let config_home =
lookup("XDG_CONFIG_HOME").or_else(|| lookup("HOME").map(|h| h.join(".config")));
if config_home.is_none() {
log::debug!(
"Neither $XDG_CONFIG_HOME nor $HOME is set in the user manager's environment"
);
}
config_home.map(|config_home| config_home.join("systemd/user"))
}
};
if user_config_unit_dir.is_none() {
log::debug!(
"Could not determine $XDG_CONFIG_HOME/systemd/user; \
units shadowed by ~/.config will not be considered for migration"
);
}
// Units active from a non-/etc location that the new generation defines
// in /etc/systemd/user. Pass 1 skips these (FragmentPath filter); pass 2
// brings the /etc definition into effect once /etc has won. Two cases:
// * ~/.config/systemd/user (home-manager): shadows /etc, so wait for
// the per-user activation (sd-switch) to remove its copy.
// * anywhere else outside /etc ($XDG_DATA_HOME, $XDG_DATA_DIRS, ...):
// /etc outranks these, so only act when /etc is gaining the unit;
// if the previous generation already had it, leave it alone.
// Pass 2's `now_etc` check verifies /etc actually won before acting.
let migration_candidates: Vec<String> = current_active_units
.iter()
.filter(|(unit, _)| new_unit_dir.join(unit).exists())
.filter(|(_, unit_state)| {
!unit_state
.filter(|(unit, unit_state)| {
let Ok(fragment_path) = unit_state
.proxy
.get("org.freedesktop.systemd1.Unit", "FragmentPath")
.map(|p: String| p.starts_with(fragment_prefix))
.unwrap_or(false)
.get::<String>("org.freedesktop.systemd1.Unit", "FragmentPath")
else {
return false;
};
let fragment_parent = Path::new(&fragment_path).parent();
// Already in /etc: handled by pass 1.
if fragment_parent == Some(fragment_dir) {
return false;
}
// Loaded from ~/.config/systemd/user, which shadows /etc.
if let Some(dir) = &user_config_unit_dir {
if fragment_parent == Some(dir.as_path()) {
return true;
}
}
// Elsewhere: only act if /etc is gaining the unit this switch.
!old_unit_dir.join(unit).exists()
})
.map(|(unit, _)| unit.clone())
.collect();
@@ -1422,7 +1475,7 @@ fn do_user_switch(parent_exe: String) -> anyhow::Result<()> {
collect_unit_changes(
&toplevel,
scope,
&old_toplevel.join(scope.etc_dir()),
&old_unit_dir,
&new_unit_dir,
&current_active_units,
&mut units_to_stop,
@@ -1577,7 +1630,7 @@ fn do_user_switch(parent_exe: String) -> anyhow::Result<()> {
let now_etc = unit_state
.proxy
.get("org.freedesktop.systemd1.Unit", "FragmentPath")
.map(|p: String| p.starts_with(fragment_prefix))
.map(|p: String| Path::new(&p).parent() == Some(fragment_dir))
.unwrap_or(false);
if !now_etc {
// Still shadowed (or read error); leave it alone.