Arrancar / Parar / Reiniciar servicios en RHEL 7 y CentOS 7

En RHEL 7 y CentOS 7 (ver guía de instalación)la forma de controlar los servicios del sistema cambia completamente. Pasamos del uso del comando «service» y de la control de servicios a través de «/etc/init.d» a la gestión a través del service manager systemctl.

La explicación la tenemos directamente en el fichero README de /etc/init.d:

# more /etc/init.d/README 
You are looking for the traditional init scripts in /etc/rc.d/init.d,
and they are gone?

Here's an explanation on what's going on:

You are running a systemd-based OS where traditional init scripts have
been replaced by native systemd services files. Service files provide
very similar functionality to init scripts. To make use of service
files simply invoke "systemctl", which will output a list of all
currently running services (and other units). Use "systemctl
list-unit-files" to get a listing of all known unit files, including
stopped, disabled and masked ones. Use "systemctl start
foobar.service" and "systemctl stop foobar.service" to start or stop a
service, respectively. For further details, please refer to
systemctl(1).

Note that traditional init scripts continue to function on a systemd
system. An init script /etc/rc.d/init.d/foobar is implicitly mapped
into a service unit foobar.service during system initialization.

Thank you!

Further reading:
        man:systemctl(1)
        man:systemd(1)
        http://0pointer.de/blog/projects/systemd-for-admins-3.html
        http://www.freedesktop.org/wiki/Software/systemd/Incompatibilities

Vamos a ver entonces los comandos básicos de gestión de servicios con systemctl.

Listar servicios del sistema

El comando systemctl sin parámetros nos mostrará el listado de todos los servicios del sistema, incluyendo los que están activos, parados o en estado fallido.

# systemctl 
UNIT                                                LOAD   ACTIVE SUB       DESCRIPTION
proc-sys-fs-binfmt_misc.automount                   loaded active waiting   Arbitrary Executable File Formats File System Automo
sys-devices-pci0...et1:0:0-1:0:0:0-block-sr0.device loaded active plugged   VBOX_CD-ROM
sys-devices-pci0...0-0000:00:03.0-net-enp0s3.device loaded active plugged   PRO/1000 MT Desktop Adapter
sys-devices-pci0...-0000:00:05.0-sound-card0.device loaded active plugged   82801AA AC'97 Audio Controller
sys-devices-pci0...:0-2:0:0:0-block-sda-sda1.device loaded active plugged   VBOX_HARDDISK
sys-devices-pci0...:0-2:0:0:0-block-sda-sda2.device loaded active plugged   LVM PV F3zoLx-uSaP-faJK-Vhz7-iJC4-XFml-QjX37E on /de
sys-devices-pci0...et2:0:0-2:0:0:0-block-sda.device loaded active plugged   VBOX_HARDDISK

Los servicios son llamados UNITS, y como veis podemos visualizar el estado del proceso, si está cargado en el sistema, descripción…

El parámetro list-units muestra la misma información:

# systemctl list-units

Ver estado de un servicio

Tan sencillo como pasar el parámetro status + el servicio. Vamos a ver el estado del firewall:

# systemctl status firewalld.service
firewalld.service - firewalld - dynamic firewall daemon
   Loaded: loaded (/usr/lib/systemd/system/firewalld.service; enabled)
   Active: active (running) since sáb 2014-08-23 17:51:42 CEST; 9min ago
 Main PID: 549 (firewalld)
   CGroup: /system.slice/firewalld.service
           └─549 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid

ago 23 17:51:42 localhost.localdomain systemd[1]: Started firewalld - dynamic firewall daemon.

Como podéis observar nos ofrece mucha más información que el típico status que teníamos en «init.d» y «service». Incluso podemos ver el log completo o sólo la parte que engloba el arranque:

# systemctl status network.service
network.service - LSB: Bring up/down networking
   Loaded: loaded (/etc/rc.d/init.d/network)
   Active: active (exited) since sáb 2014-08-23 17:51:45 CEST; 10min ago
  Process: 830 ExecStart=/etc/rc.d/init.d/network start (code=exited, status=0/SUCCESS)

ago 23 17:51:43 localhost.localdomain systemd[1]: Starting LSB: Bring up/down networking...
ago 23 17:51:44 localhost.localdomain network[830]: Bringing up loopback interface:  Could not load file '/etc/sysconfig...g-lo'
ago 23 17:51:44 localhost.localdomain network[830]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
ago 23 17:51:44 localhost.localdomain network[830]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
ago 23 17:51:44 localhost.localdomain network[830]: Could not load file '/etc/sysconfig/network-scripts/ifcfg-lo'
ago 23 17:51:44 localhost.localdomain network[830]: [  OK  ]
ago 23 17:51:45 localhost.localdomain network[830]: Bringing up interface enp0s3:  [  OK  ]
ago 23 17:51:45 localhost.localdomain systemd[1]: Started LSB: Bring up/down networking.
Hint: Some lines were ellipsized, use -l to show in full.

Arrancar, parar y reiniciar servicios

Ya sabemos los servicios que hay en el sistema, así que podemos invocarlos para iniciarlos, pararlos o reiniciarlos:

Iniciar servicio:

# systemctl start firewalld.service

Parar servicio:

# systemctl stop firewalld.service

Reiniciar servicio:

# systemctl restart firewalld.service

Recargar servicio (si lo permite):

# systemctl reload firewalld.service

chkconfig vs systemctl

Esto lo quiero explicar más detenidamente en otro artículo, pero sólo añadir que chkconfig también es sustituido por systemctl.

Por ejemplo, para quitar la red del arranque:

[root@localhost ~]# systemctl disable NetworkManager.service
rm '/etc/systemd/system/multi-user.target.wants/NetworkManager.service'
rm '/etc/systemd/system/dbus-org.freedesktop.NetworkManager.service'
rm '/etc/systemd/system/dbus-org.freedesktop.nm-dispatcher.service'

Y vemos que al lanzar un status aparece el servicio activo pero «disabled» en el arranque:

[root@localhost ~]# systemctl status NetworkManager.service
NetworkManager.service - Network Manager
   Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; disabled)
   Active: active (running) since sáb 2014-08-23 17:51:43 CEST; 15min ago
 Main PID: 676 (NetworkManager)

Si lo volvemos a configurar:

[root@localhost ~]# systemctl enable NetworkManager.service
ln -s '/usr/lib/systemd/system/NetworkManager.service' '/etc/systemd/system/dbus-org.freedesktop.NetworkManager.service'
ln -s '/usr/lib/systemd/system/NetworkManager.service' '/etc/systemd/system/multi-user.target.wants/NetworkManager.service'
ln -s '/usr/lib/systemd/system/NetworkManager-dispatcher.service' '/etc/systemd/system
/dbus-org.freedesktop.nm-dispatcher.service'

[root@localhost ~]# systemctl status NetworkManager.service
NetworkManager.service - Network Manager
   Loaded: loaded (/usr/lib/systemd/system/NetworkManager.service; enabled)
   Active: active (running) since sáb 2014-08-23 17:51:43 CEST; 16min ago

Esto es lo que tenéis que saber para iniciaros con systemctl. Recordad que la página man del comando tiene toda la información necesaria para administración avanzada. En algún otro artículo iré poniendo más funcionalidades interesantes (que no son pocas).