Linger changes when an account’s systemd user manager is kept available. With lingering enabled, logind can start that manager at boot and retain it after the account’s login sessions end. This supports unattended work owned by a normal account. The flag controls manager lifetime; individual services still have their own activation, failure, shutdown, and installation rules.

When it breaks

Enabling linger does not enable every unit file found in the account’s configuration directory. A service must be requested through enablement, a dependency, a timer, a socket, or another explicit activation path. A manager can be running correctly while the intended application remains inactive. Check both objects instead of interpreting the linger flag as a list of running services.

Processes do not survive a machine reboot. Linger can arrange for a new user manager to start at boot, and enabled units can then start new processes. Their previous in-memory state is gone. An encrypted or late-mounted home can also make unit files or application data unavailable at the time the manager starts. Persist required state and make boot-time dependencies intentional.

Linger is not an instruction to restart a crashed application forever or to adopt arbitrary shell jobs into managed services. Restart policy, resource limits, and logind’s treatment of session processes are separate controls. A stable background role needs a real user unit and an observed result, not just a shell command launched before logout.

Check it quickly

Run this Python script as an administrator in a disposable Linux system with systemd, logind, user D-Bus support, and account-management tools. The recorded environment was Debian 12 with systemd 252.39. It creates a temporary account and home, enables lingering only for that account, and removes its changes afterward. No login session is opened for the account:

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)

After enable-linger, the user manager becomes active and its bus appears. logind reports lingering enabled and an empty session list. However, the installed worker unit is still inactive. This confirms that keeping the manager available is different from requesting the application to run, even though the configuration file already exists.

The script then enables and starts the worker through the correct user manager. Its installation section links it to the user’s default target, while the explicit start begins current execution. A PID marker identifies the actual worker. The controller uses setpriv and the user’s runtime bus, so the control command itself does not quietly create a login session.

Restarting the system-level user@UID.service replaces the account manager. The enabled worker subsequently publishes a different PID, and the new user manager reports that same process as its main worker. The session list remains empty. This tests reconstruction from persistent unit enablement across a real manager restart, rather than merely observing the same process for a little longer.

Disabling the worker without a stop request leaves the current service active. Disablement removes future enablement links; it is not an implicit termination command. The script checks that distinction, then explicitly stops the worker and disables lingering. With no sessions remaining, the account manager becomes inactive under the configured stop policy.

Cleanup disables lingering again if needed, stops the experiment’s manager and runtime-directory unit, and deletes the temporary account and home. The exercise deliberately uses temporary configuration and does not reboot the machine. Its reboot-related statements come from the documented lifecycle contract; the observed process replacement is a manager restart, not a claimed reboot test.

Operate an unattended account deliberately

Keep the account’s enabled units reviewable and remove services that are no longer needed. A service that remains available after logout can retain memory, open files, credentials, and network listeners. Ordinary user authority limits some actions but still permits everything granted to that identity. Use suitable permissions and supported resource controls for the actual workload.

Make configuration and credentials available through mechanisms that work without an interactive shell. A successful launch from a terminal does not prove unattended startup has the same environment. Verify working directories, input paths, and access after restarting the manager, then perform a real boot test when boot-time availability is a deployment requirement.

When retiring the role, distinguish disabling a service, stopping current execution, disabling linger, and deleting account data. Other sessions or activation paths may still matter. Inspect the account’s actual manager and service states after the intended change. The useful guarantee is a documented unattended lifecycle with explicit activation and shutdown, not the indefinite survival of one PID.

Further reading

Sources