Linger 延长 systemd 用户管理器在登录之外的寿命

from pathlib import Path
from tempfile import TemporaryDirectory
import os,pwd,subprocess,time,uuid

name='xbcatm-linger-'+uuid.uuid4().hex[:8];unit='field-worker.service'
def run(*args):
    result=subprocess.run(args,capture_output=True,text=True,timeout=20)
    assert result.returncode==0,(args,result.stderr)
    return result.stdout.strip()
def wait_for(check,seconds=5):
    deadline=time.monotonic()+seconds
    while not check():
        assert time.monotonic()<deadline,'state transition timed out';time.sleep(0.05)
with TemporaryDirectory(prefix=name+'-',dir='/run') as directory:
    root=Path(directory);root.chmod(0o755);home=root/'home';home.mkdir()
    run('useradd','--no-create-home','--user-group','--home-dir',str(home),'--shell','/bin/sh',name)
    account=pwd.getpwnam(name);uid=account.pw_uid;gid=account.pw_gid;manager=f'user@{uid}.service'
    def userctl(*args):
        return run('setpriv','--reuid='+str(uid),'--regid='+str(gid),'--init-groups',
                   'env',f'XDG_RUNTIME_DIR=/run/user/{uid}',f'DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/{uid}/bus',
                   'systemctl','--user',*args)
    def manager_value(key):return run('systemctl','show',manager,'-p',key,'--value')
    try:
        units=home/'.config/systemd/user';units.mkdir(parents=True)
        (home/'worker.py').write_text("from pathlib import Path\nimport os,time\np=Path(__file__).with_name('worker-pid');t=p.with_suffix('.tmp');t.write_text(str(os.getpid()));t.replace(p)\ntime.sleep(60)\n")
        (units/unit).write_text('[Service]\nType=exec\nExecStart=/usr/bin/python3 %h/worker.py\n[Install]\nWantedBy=default.target\n')
        for path in [home,*home.rglob('*')]:os.chown(path,uid,gid)
        run('loginctl','enable-linger',name)
        wait_for(lambda:Path(f'/run/user/{uid}/bus').exists())
        assert run('loginctl','show-user',name,'-p','Linger','--value')=='yes'
        assert run('loginctl','show-user',name,'-p','Sessions','--value')==''
        assert manager_value('ActiveState')=='active'
        assert userctl('show',unit,'-p','ActiveState','--value')=='inactive'
        print('linger starts a manager with zero login sessions; merely installing a user unit does not start it')
        userctl('enable','--now',unit);wait_for(lambda:(home/'worker-pid').exists())
        first=(home/'worker-pid').read_text();first_manager=manager_value('MainPID')
        run('systemctl','restart',manager)
        wait_for(lambda:Path(f'/run/user/{uid}/bus').exists() and (home/'worker-pid').read_text()!=first)
        assert manager_value('MainPID')!=first_manager
        assert userctl('show',unit,'-p','MainPID','--value')==(home/'worker-pid').read_text()
        assert run('loginctl','show-user',name,'-p','Sessions','--value')==''
        print('enabled user service starts as a new process after a real manager restart')
        userctl('disable',unit)
        assert userctl('show',unit,'-p','ActiveState','--value')=='active'
        print('disable removes future enablement but does not stop the current service')
        userctl('stop',unit);run('loginctl','disable-linger',name)
        wait_for(lambda:manager_value('ActiveState')=='inactive',seconds=20)
        print('with no sessions and linger disabled, user manager stops after policy delay')
    finally:
        run('loginctl','disable-linger',name)
        run('systemctl','stop',manager,f'user-runtime-dir@{uid}.service')
        run('userdel',name)