Execute systemctl command asynchronously and do not wait for its completion.

Use --no-block parameter to request asynchronous behavior.

Inspect service status.

$ sudo systemctl status sssd
● sssd.service - System Security Services Daemon
     Loaded: loaded (/lib/systemd/system/sssd.service; enabled; vendor preset: enabled)
     Active: active (running) since Sun 2021-10-03 17:00:21 CEST; 8h ago
   Main PID: 1827 (sssd)                                                                                                        
      Tasks: 4 (limit: 1105)    
     Memory: 47.8M                              
        CPU: 1.538s                                                                                                             
     CGroup: /system.slice/sssd.service                                                                                         
             ├─1827 /usr/sbin/sssd -i --logger=files
             ├─1828 /usr/libexec/sssd/sssd_be --domain octocat.lab --uid 0 --gid 0 --logger=files
             ├─1829 /usr/libexec/sssd/sssd_nss --uid 0 --gid 0 --logger=files
             └─1830 /usr/libexec/sssd/sssd_pam --uid 0 --gid 0 --logger=files
                                                                
Oct 03 17:00:21 ad.octocat.lab systemd[1]: Starting System Security Services Daemon...
Oct 03 17:00:21 ad.octocat.lab sssd[1827]: Starting up                                                                          
Oct 03 17:00:21 ad.octocat.lab sssd_be[1828]: Starting up                                                                       
Oct 03 17:00:21 ad.octocat.lab sssd_nss[1829]: Starting up                                                                      
Oct 03 17:00:21 ad.octocat.lab sssd_pam[1830]: Starting up
Oct 03 17:00:21 ad.octocat.lab systemd[1]: Started System Security Services Daemon.   
Oct 03 18:32:26 ad.octocat.lab sssd_be[1828]: Backend is online
Oct 03 21:18:54 ad.octocat.lab sssd_be[1828]: Backend is offline 
Oct 03 21:25:23 ad.octocat.lab sssd_be[1828]: Backend is online

Execute restart operation asynchronously to not wait for its completion.

$ sudo systemctl restart sssd --no-block; 

Command will exit immediately, so you will notice different states as it is restarted.

$ sudo systemctl status sssd
● sssd.service - System Security Services Daemon          
     Loaded: loaded (/lib/systemd/system/sssd.service; enabled; vendor preset: enabled)
     Active: deactivating (stop-sigterm) since Mon 2021-10-04 01:09:11 CEST; 6ms ago                                                                                                                                                                            
   Main PID: 1827 (sssd)
      Tasks: 1 (limit: 1105)
     Memory: 29.3M
        CPU: 1.546s
     CGroup: /system.slice/sssd.service
             └─1827 [sssd]

Oct 03 17:00:21 ad.octocat.lab sssd[1827]: Starting up
Oct 03 17:00:21 ad.octocat.lab sssd_be[1828]: Starting up
Oct 03 17:00:21 ad.octocat.lab sssd_nss[1829]: Starting up
Oct 03 17:00:21 ad.octocat.lab sssd_pam[1830]: Starting up
Oct 03 17:00:21 ad.octocat.lab systemd[1]: Started System Security Services Daemon.
Oct 03 18:32:26 ad.octocat.lab sssd_be[1828]: Backend is online
Oct 03 21:18:54 ad.octocat.lab sssd_be[1828]: Backend is offline 
Oct 03 21:25:23 ad.octocat.lab sssd_be[1828]: Backend is online
Oct 04 01:09:11 ad.octocat.lab sssd_be[1828]: Shutting down (status = 0)
Oct 04 01:09:11 ad.octocat.lab systemd[1]: Stopping System Security Services Daemon...
$ sudo  systemctl status sssd                                                                                                                                       
● sssd.service - System Security Services Daemon
     Loaded: loaded (/lib/systemd/system/sssd.service; enabled; vendor preset: enabled)
     Active: activating (start) since Mon 2021-10-04 01:09:11 CEST; 8ms ago
   Main PID: 5752 (sssd)
      Tasks: 1 (limit: 1105)
     Memory: 288.0K
        CPU: 1ms
     CGroup: /system.slice/sssd.service
             └─5752 /usr/sbin/sssd -i --logger=files

Oct 04 01:09:11 ad.octocat.lab systemd[1]: Starting System Security Services Daemon...
$ sudo systemctl status sssd
● sssd.service - System Security Services Daemon
     Loaded: loaded (/lib/systemd/system/sssd.service; enabled; vendor preset: enabled)
     Active: active (running) since Mon 2021-10-04 01:09:11 CEST; 6s ago
   Main PID: 5752 (sssd)
      Tasks: 4 (limit: 1105)
     Memory: 46.0M
        CPU: 327ms
     CGroup: /system.slice/sssd.service
             ├─5752 /usr/sbin/sssd -i --logger=files
             ├─5755 /usr/libexec/sssd/sssd_be --domain octocat.lab --uid 0 --gid 0 --logger=files
             ├─5756 /usr/libexec/sssd/sssd_nss --uid 0 --gid 0 --logger=files
             └─5757 /usr/libexec/sssd/sssd_pam --uid 0 --gid 0 --logger=files

Oct 04 01:09:11 ad.octocat.lab systemd[1]: Starting System Security Services Daemon...
Oct 04 01:09:11 ad.octocat.lab sssd[5752]: Starting up
Oct 04 01:09:11 ad.octocat.lab sssd_be[5755]: Starting up
Oct 04 01:09:11 ad.octocat.lab sssd_nss[5756]: Starting up
Oct 04 01:09:11 ad.octocat.lab sssd_pam[5757]: Starting up
Oct 04 01:09:11 ad.octocat.lab systemd[1]: Started System Security Services Daemon.

This can be useful when executing automation scripts that do not need to wait and block further execution.