Systemctl : RHEL 7: How to check, start, stop, and manage units/services ?
Today we will look various systemctl commands to check units/services, start/stop/restart them.
In short how to play/work with systemctl commands to manage services/units.
1. How to see all units loaded on to the system.
[root@host-1-89 ~]# systemctl UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File System Automount Po sys-devices-pci0000:00-0000:00:03.0-net-ens3.device loaded active plugged 82540EM Gigabit Ethernet Controller (QEMU Virtual Machine) sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda-sda1.device loaded active plugged QEMU_HARDDISK 1 sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda-sda2.device loaded active plugged LVM PV kIogiH-f548-AELA-N sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda.device loaded active plugged QEMU_HARDDISK sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:1-1:0:1:0-block-sdb-sdb1.device loaded active plugged QEMU_HARDDISK 1 sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:1-1:0:1:0-block-sdb.device loaded active plugged QEMU_HARDDISK sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:2-1:0:2:0-block-sr0.device loaded active plugged QEMU_CD-ROM sys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 sys-devices-pnp0-00:05-tty-ttyS0.device loaded active plugged /sys/devices/pnp0/00:05/tty/ttyS0 sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0 sys-devices-virtual-net-virbr0.device loaded active plugged /sys/devices/virtual/net/virbr0 sys-devices-virtual-net-virbr0\x2dnic.device loaded active plugged /sys/devices/virtual/net/virbr0-nic sys-module-configfs.device loaded active plugged /sys/module/configfs sys-subsystem-net-devices-ens3.device loaded active plugged 82540EM Gigabit Ethernet Controller (QEMU Virtual Machine) sys-subsystem-net-devices-virbr0.device loaded active plugged /sys/subsystem/net/devices/virbr0 sys-subsystem-net-devices-virbr0\x2dnic.device loaded active plugged /sys/subsystem/net/devices/virbr0-nic -.mount loaded active mounted / boot.mount loaded active mounted /boot dev-hugepages.mount loaded active mounted Huge Pages File System dev-mqueue.mount loaded active mounted POSIX Message Queue File System proc-fs-nfsd.mount loaded active mounted NFSD configuration filesystem run-user-0.mount loaded active mounted /run/user/0 run-user-42.mount loaded active mounted /run/user/42 sys-kernel-config.mount loaded active mounted Configuration File System sys-kernel-debug.mount loaded active mounted Debug File System var-lib-nfs-rpc_pipefs.mount loaded active mounted RPC Pipe File System brandbot.path loaded active waiting Flexible branding cups.path loaded active waiting CUPS Printer Service Spool systemd-ask-password-plymouth.path loaded active waiting Forward Password Requests to Plymouth Directory Watch systemd-ask-password-wall.path loaded active waiting Forward Password Requests to Wall Directory Watch session-1.scope loaded active running Session 1 of user root session-c1.scope loaded active running Session c1 of user gdm abrt-ccpp.service loaded active exited Install ABRT coredump hook abrt-oops.service loaded active running ABRT kernel log watcher abrt-xorg.service loaded active running ABRT Xorg log watcher abrtd.service loaded active running ABRT Automated Bug Reporting Tool accounts-daemon.service loaded active running Accounts Service acpid.service loaded active running ACPI Event Daemon alsa-state.service loaded active running Manage Sound Card State (restore and store) atd.service loaded active running Job spooling tools auditd.service loaded active running Security Auditing Service avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack blk-availability.service loaded active exited Availability of block devices chronyd.service loaded active running NTP client/server colord.service loaded active running Manage, Install and Generate Color Profiles dbus.service loaded active running D-Bus System Message Bus gdm.service loaded active running GNOME Display Manager user-0.slice loaded active active user-0.slice user-42.slice loaded active active user-42.slice user.slice loaded active active User and Session Slice avahi-daemon.socket loaded active running Avahi mDNS/DNS-SD Stack Activation Socket cups.socket loaded active listening CUPS Printing Service Sockets dbus.socket loaded active running D-Bus System Message Bus Socket dm-event.socket loaded active listening Device-mapper event daemon FIFOs iscsid.socket loaded active listening Open-iSCSI iscsid Socket iscsiuio.socket loaded active listening Open-iSCSI iscsiuio Socket lvm2-lvmetad.socket loaded active running LVM2 metadata daemon socket lvm2-lvmpolld.socket loaded active listening LVM2 poll daemon socket rpcbind.socket loaded active running RPCbind Server Activation Socket systemd-initctl.socket loaded active listening /dev/initctl Compatibility Named Pipe systemd-journald.socket loaded active running Journal Socket systemd-shutdownd.socket loaded active listening Delayed Shutdown Socket systemd-udevd-control.socket loaded active running udev Control Socket systemd-udevd-kernel.socket loaded active running udev Kernel Socket telnet.socket loaded active listening Telnet Server Activation Socket virtlogd.socket loaded active listening Virtual machine log manager socket dev-disk-by\x2duuid-971d09b6\x2d8ce8\x2d49c7\x2d9ec9\x2d16b0155f42cf.swap loaded active active /dev/disk/by-uuid/971d09b6-8ce8-49c7-9ec9-1 basic.target loaded active active Basic System cryptsetup.target loaded active active Encrypted Volumes getty.target loaded active active Login Prompts graphical.target loaded active active Graphical Interface local-fs-pre.target loaded active active Local File Systems (Pre) local-fs.target loaded active active Local File Systems paths.target loaded active active Paths remote-fs-pre.target loaded active active Remote File Systems (Pre) remote-fs.target loaded active active Remote File Systems rpcbind.target loaded active active RPC Port Mapper slices.target loaded active active Slices sockets.target loaded active active Sockets swap.target loaded active active Swap sysinit.target loaded active active System Initialization timers.target loaded active active Timers systemd-tmpfiles-clean.timer loaded active waiting Daily Cleanup of Temporary Directories LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 152 loaded units listed. Pass --all to see loaded but inactive units, too. To show all installed unit files use 'systemctl list-unit-files'. lines 129-160/160 (END)
2. What is the difference between systemctl and “systemctl list-units”
There is no difference between them.
Both commands displays all the units loaded on to the system.
root@host-1-89 ~]# systemctl | wc -l 160 [root@host-1-89 ~]# systemctl list-units | wc -l 160 [root@host-1-89 ~]#
3. See all system services including the ones disabled/inactive.
[root@host-1-89 ~]# systemctl --all UNIT LOAD ACTIVE SUB DESCRIPTION proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File System Automoun dev-block-8:2.device loaded active plugged LVM PV kIogiH-f548-AELA-NMVK-sbr7-9u7j-2K6MDz on /dev/ dev-cdrom.device loaded active plugged QEMU_CD-ROM dev-centos_lvm-root.device loaded active plugged /dev/centos_lvm/root dev-disk-by\x2did-dm\x2dname\x2dcentos_lvm\x2droot.device loaded active plugged /dev/disk/by-id/dm-name-centos_lvm-root dev-disk-by\x2did-dm\x2duuid\x2dLVM\x2dqGpE995l8Lvs0XM4Zz0FDUO5sY5Qm6P5xnNIQ2ct1mUqaRBkjOGrNIFUwte2ciYM.device loaded active plugged / dev-disk-by\x2did-lvm\x2dpv\x2duuid\x2dkIogiH\x2df548\x2dAELA\x2dNMVK\x2dsbr7\x2d9u7j\x2d2K6MDz.device loaded active plugged LVM PV kI dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_CD\x2dROM_cdrom2.device loaded active plugged QEMU_CD-ROM dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_HARDDISK_disk0.device loaded active plugged QEMU_HARDDISK dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_HARDDISK_disk0\x2dpart1.device loaded active plugged QEMU_HARDDISK 1 dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_HARDDISK_disk0\x2dpart2.device loaded active plugged LVM PV kIogiH-f548-AELA-NMVK-sbr7-9u7j-2K6MD dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_HARDDISK_disk1.device loaded active plugged QEMU_HARDDISK dev-disk-by\x2did-scsi\x2d0QEMU_QEMU_HARDDISK_disk1\x2dpart1.device loaded active plugged QEMU_HARDDISK 1 dev-disk-by\x2dpath-virtio\x2dpci\x2d0000:00:04.0\x2dscsi\x2d0:0:0:0.device loaded active plugged QEMU_HARDDISK dev-disk-by\x2dpath-virtio\x2dpci\x2d0000:00:04.0\x2dscsi\x2d0:0:0:0\x2dpart1.device loaded active plugged QEMU_HARDDISK 1 dev-mapper-centos_lvm\x2droot.device loaded active plugged /dev/mapper/centos_lvm-root dev-sda.device loaded active plugged QEMU_HARDDISK dev-sda1.device loaded active plugged QEMU_HARDDISK 1 dev-sda2.device loaded active plugged LVM PV kIogiH-f548-AELA-NMVK-sbr7-9u7j-2K6MDz on /dev/ dev-sdb.device loaded active plugged QEMU_HARDDISK dev-sdb1.device loaded active plugged QEMU_HARDDISK 1 dev-sr0.device loaded active plugged QEMU_CD-ROM dev-ttyS0.device loaded active plugged /dev/ttyS0 dev-ttyS1.device loaded active plugged /dev/ttyS1 dev-ttyS2.device loaded active plugged /dev/ttyS2 dev-ttyS3.device loaded active plugged /dev/ttyS3 sys-devices-pci0000:00-0000:00:03.0-net-ens3.device loaded active plugged 82540EM Gigabit Ethernet Controller (QEMU Virtual Mach sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda-sda1.device loaded active plugged QEMU_HARDDISK 1 sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda-sda2.device loaded active plugged LVM PV kIogiH-f548-A sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:0-1:0:0:0-block-sda.device loaded active plugged QEMU_HARDDISK sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:1-1:0:1:0-block-sdb-sdb1.device loaded active plugged QEMU_HARDDISK 1 sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:1-1:0:1:0-block-sdb.device loaded active plugged QEMU_HARDDISK sys-devices-pci0000:00-0000:00:04.0-virtio0-host1-target1:0:2-1:0:2:0-block-sr0.device loaded active plugged QEMU_CD-ROM sys-devices-platform-serial8250-tty-ttyS1.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS1 sys-devices-platform-serial8250-tty-ttyS2.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS2 sys-devices-platform-serial8250-tty-ttyS3.device loaded active plugged /sys/devices/platform/serial8250/tty/ttyS3 sys-devices-pnp0-00:05-tty-ttyS0.device loaded active plugged /sys/devices/pnp0/00:05/tty/ttyS0 sys-devices-virtual-block-dm\x2d0.device loaded active plugged /sys/devices/virtual/block/dm-0 sys-devices-virtual-net-virbr0.device loaded active plugged /sys/devices/virtual/net/virbr0 sys-devices-virtual-net-virbr0\x2dnic.device loaded active plugged /sys/devices/virtual/net/virbr0-nic sys-module-configfs.device loaded active plugged /sys/module/configfs sys-subsystem-net-devices-ens3.device loaded active plugged 82540EM Gigabit Ethernet Controller (QEMU Virtual Mach sys-subsystem-net-devices-virbr0.device loaded active plugged /sys/subsystem/net/devices/virbr0 sys-subsystem-net-devices-virbr0\x2dnic.device loaded active plugged /sys/subsystem/net/devices/virbr0-nic -.mount loaded active mounted / boot.mount loaded active mounted /boot dev-hugepages.mount loaded active mounted Huge Pages File System dev-mqueue.mount loaded active mounted POSIX Message Queue File System proc-fs-nfsd.mount loaded active mounted NFSD configuration filesystem proc-sys-fs-binfmt_misc.mount loaded inactive dead Arbitrary Executable File Formats File System run-user-0.mount loaded active mounted /run/user/0 run-user-42.mount loaded active mounted /run/user/42 sys-fs-fuse-connections.mount loaded inactive dead FUSE Control File System sys-kernel-config.mount loaded active mounted Configuration File System sys-kernel-debug.mount loaded active mounted Debug File System tmp.mount loaded inactive dead Temporary Directory var-lib-nfs-rpc_pipefs.mount loaded active mounted RPC Pipe File System brandbot.path loaded active waiting Flexible branding cups.path loaded active waiting CUPS Printer Service Spool systemd-ask-password-console.path loaded inactive dead Dispatch Password Requests to Console Directory Watch systemd-ask-password-plymouth.path loaded active waiting Forward Password Requests to Plymouth Directory Watch systemd-ask-password-wall.path loaded active waiting Forward Password Requests to Wall Directory Watch session-1.scope loaded active running Session 1 of user root session-c1.scope loaded active running Session c1 of user gdm abrt-ccpp.service loaded active exited Install ABRT coredump hook abrt-oops.service loaded active running ABRT kernel log watcher abrt-vmcore.service loaded inactive dead Harvest vmcores for ABRT abrt-xorg.service loaded active running ABRT Xorg log watcher abrtd.service loaded active running ABRT Automated Bug Reporting Tool accounts-daemon.service loaded active running Accounts Service acpid.service loaded active running ACPI Event Daemon alsa-restore.service loaded inactive dead Save/Restore Sound Card State alsa-state.service loaded active running Manage Sound Card State (restore and store) ● apparmor.service not-found inactive dead apparmor.service atd.service loaded active running Job spooling tools auditd.service loaded active running Security Auditing Service auth-rpcgss-module.service loaded inactive dead Kernel Module supporting RPCSEC_GSS avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack blk-availability.service loaded active exited Availability of block devices brandbot.service loaded inactive dead Flexible Branding Service chronyd.service loaded active running NTP client/server colord.service loaded active running Manage, Install and Generate Color Profiles cpupower.service loaded inactive dead Configure CPU power related settings cups.service loaded inactive dead CUPS Printing Service dbus.service loaded active running D-Bus System Message Bus dm-event.service loaded inactive dead Device-mapper event daemon dmraid-activation.service loaded inactive dead Activation of DM RAID sets dracut-shutdown.service loaded inactive dead Restore /run/initramfs emergency.service loaded inactive dead Emergency Shell ● exim.service not-found inactive dead exim.service fcoe.service loaded inactive dead Open-FCoE Inititator. ● firewalld.service masked inactive dead firewalld.service firstboot-graphical.service loaded inactive dead firstboot configuration program (graphical mode) gdm.service loaded active running GNOME Display Manager getty@tty1.service loaded inactive dead Getty on tty1 gssproxy.service loaded active running GSSAPI Proxy Daemon ● initial-setup-graphical.service not-found inactive dead initial-setup-graphical.service ip6tables.service loaded active exited IPv6 firewall with ip6tables iptables.service loaded active exited IPv4 firewall with iptables irqbalance.service loaded inactive dead irqbalance daemon iscsi-shutdown.service loaded active exited Logout off all iSCSI sessions on shutdown iscsi.service loaded inactive dead Login and scanning of iSCSI devices iscsid.service loaded inactive dead Open-iSCSI iscsiuio.service loaded inactive dead iSCSI UserSpace I/O driver kdump.service loaded inactive dead Crash recovery kernel arming kmod-static-nodes.service loaded active exited Create list of required static device nodes for the cu ksm.service loaded active exited Kernel Samepage Merging ksmtuned.service loaded active running Kernel Samepage Merging (KSM) Tuning Daemon libstoragemgmt.service loaded active running libstoragemgmt plug-in server daemon libvirt-guests.service loaded inactive dead Suspend Active Libvirt Guests libvirtd.service loaded active running Virtualization daemon ● livesys.service not-found inactive dead livesys.service lldpad.service loaded inactive dead Link Layer Discovery Protocol Agent Daemon. ● lvm2-activation-early.service not-found inactive dead lvm2-activation-early.service ● lvm2-activation.service not-found inactive dead lvm2-activation.service lvm2-lvmetad.service loaded active running LVM2 metadata daemon lvm2-lvmpolld.service loaded inactive dead LVM2 poll daemon lvm2-monitor.service loaded active exited Monitoring of LVM2 mirrors, snapshots etc. using dmeve lvm2-pvscan@8:2.service loaded active exited LVM2 PV scan on device 8:2 mdmonitor.service loaded inactive dead Software RAID monitoring and management microcode.service loaded inactive dead Load CPU microcode update ModemManager.service loaded active running Modem Manager multipathd.service loaded inactive dead Device-Mapper Multipath Device Controller netcf-transaction.service loaded active exited Rollback uncommitted netcf network config change trans ● network.service loaded failed failed LSB: Bring up/down networking NetworkManager-wait-online.service loaded active exited Network Manager Wait Online plymouth-quit-wait.service loaded inactive dead Wait for Plymouth Boot Screen to Quit plymouth-quit.service loaded inactive dead Terminate Plymouth Boot Screen rhel-autorelabel-mark.service loaded inactive dead Mark the need to relabel after reboot rhel-autorelabel.service loaded inactive dead Relabel all filesystems, if necessary rhel-configure.service loaded inactive dead Reconfigure the system on administrator request rhel-dmesg.service loaded active exited Dump dmesg to /var/log/dmesg user.slice loaded active active User and Session Slice avahi-daemon.socket loaded active running Avahi mDNS/DNS-SD Stack Activation Socket cups.socket loaded active listening CUPS Printing Service Sockets dbus.socket loaded active running D-Bus System Message Bus Socket dm-event.socket loaded active listening Device-mapper event daemon FIFOs iscsid.socket loaded active listening Open-iSCSI iscsid Socket iscsiuio.socket loaded active listening Open-iSCSI iscsiuio Socket lvm2-lvmetad.socket loaded active running LVM2 metadata daemon socket lvm2-lvmpolld.socket loaded active listening LVM2 poll daemon socket rpcbind.socket loaded active running RPCbind Server Activation Socket sshd.socket loaded inactive dead OpenSSH Server Socket syslog.socket loaded inactive dead Syslog Socket systemd-initctl.socket loaded active listening /dev/initctl Compatibility Named Pipe systemd-journald.socket loaded active running Journal Socket systemd-shutdownd.socket loaded active listening Delayed Shutdown Socket LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 281 loaded units listed. To show all installed unit files use 'systemctl list-unit-files'.
4. Now suppose we want to see all the service unit files on the system.
Then we can use below command.
[root@host-1-89 ~]# systemctl --type service --all UNIT LOAD ACTIVE SUB DESCRIPTION abrt-ccpp.service loaded active exited Install ABRT coredump hook abrt-oops.service loaded active running ABRT kernel log watcher abrt-vmcore.service loaded inactive dead Harvest vmcores for ABRT abrt-xorg.service loaded active running ABRT Xorg log watcher abrtd.service loaded active running ABRT Automated Bug Reporting Tool accounts-daemon.service loaded active running Accounts Service acpid.service loaded active running ACPI Event Daemon alsa-restore.service loaded inactive dead Save/Restore Sound Card State alsa-state.service loaded active running Manage Sound Card State (restore and store) ● apparmor.service not-found inactive dead apparmor.service atd.service loaded active running Job spooling tools auditd.service loaded active running Security Auditing Service auth-rpcgss-module.service loaded inactive dead Kernel Module supporting RPCSEC_GSS avahi-daemon.service loaded active running Avahi mDNS/DNS-SD Stack blk-availability.service loaded active exited Availability of block devices brandbot.service loaded inactive dead Flexible Branding Service chronyd.service loaded active running NTP client/server colord.service loaded active running Manage, Install and Generate Color Profiles cpupower.service loaded inactive dead Configure CPU power related settings cups.service loaded inactive dead CUPS Printing Service dbus.service loaded active running D-Bus System Message Bus dm-event.service loaded inactive dead Device-mapper event daemon dmraid-activation.service loaded inactive dead Activation of DM RAID sets dracut-shutdown.service loaded inactive dead Restore /run/initramfs emergency.service loaded inactive dead Emergency Shell ● exim.service not-found inactive dead exim.service fcoe.service loaded inactive dead Open-FCoE Inititator. ● firewalld.service masked inactive dead firewalld.service firstboot-graphical.service loaded inactive dead firstboot configuration program (graphical mode) gdm.service loaded active running GNOME Display Manager getty@tty1.service loaded inactive dead Getty on tty1 gssproxy.service loaded active running GSSAPI Proxy Daemon ● initial-setup-graphical.service not-found inactive dead initial-setup-graphical.service ip6tables.service loaded active exited IPv6 firewall with ip6tables iptables.service loaded active exited IPv4 firewall with iptables irqbalance.service loaded inactive dead irqbalance daemon iscsi-shutdown.service loaded active exited Logout off all iSCSI sessions on shutdown iscsi.service loaded inactive dead Login and scanning of iSCSI devices iscsid.service loaded inactive dead Open-iSCSI iscsiuio.service loaded inactive dead iSCSI UserSpace I/O driver kdump.service loaded inactive dead Crash recovery kernel arming kmod-static-nodes.service loaded active exited Create list of required static device nodes for the cur ksm.service loaded active exited Kernel Samepage Merging ksmtuned.service loaded active running Kernel Samepage Merging (KSM) Tuning Daemon libstoragemgmt.service loaded active running libstoragemgmt plug-in server daemon libvirt-guests.service loaded inactive dead Suspend Active Libvirt Guests libvirtd.service loaded active running Virtualization daemon ● livesys.service not-found inactive dead livesys.service lldpad.service loaded inactive dead Link Layer Discovery Protocol Agent Daemon. ● lvm2-activation-early.service not-found inactive dead lvm2-activation-early.service ● lvm2-activation.service not-found inactive dead lvm2-activation.service lvm2-lvmetad.service loaded active running LVM2 metadata daemon lvm2-lvmpolld.service loaded inactive dead LVM2 poll daemon lvm2-monitor.service loaded active exited Monitoring of LVM2 mirrors, snapshots etc. using dmeven lvm2-pvscan@8:2.service loaded active exited LVM2 PV scan on device 8:2 mdmonitor.service loaded inactive dead Software RAID monitoring and management microcode.service loaded inactive dead Load CPU microcode update ModemManager.service loaded active running Modem Manager multipathd.service loaded inactive dead Device-Mapper Multipath Device Controller netcf-transaction.service loaded active exited Rollback uncommitted netcf network config change transa ● network.service loaded failed failed LSB: Bring up/down networking NetworkManager-wait-online.service loaded active exited Network Manager Wait Online NetworkManager.service loaded active running Network Manager nfs-config.service loaded inactive dead Preprocess NFS configuration nfs-idmapd.service loaded active running NFSv4 ID-name mapping service nfs-mountd.service loaded active running NFS Mount Daemon nfs-server.service loaded active exited NFS server and services LOAD = Reflects whether the unit definition was properly loaded. ACTIVE = The high-level unit activation state, i.e. generalization of SUB. SUB = The low-level unit activation state, values depend on unit type. 146 loaded units listed. To show all installed unit files use 'systemctl list-unit-files'.
5. Start/Stop a Unit.
[root@host-1-129 ~]# systemctl | grep -i cups cups.path loaded active waiting CUPS Printer Service Spool cups.socket loaded active listening CUPS Printing Service Sockets [root@host-1-129 ~]# systemctl stop cups.path [root@host-1-129 ~]# systemctl | grep -i cups cups.socket loaded active listening CUPS Printing Service Sockets [root@host-1-129 ~]# systemctl start cups.path [root@host-1-129 ~]# systemctl | grep -i cups cups.path loaded active waiting CUPS Printer Service Spool cups.socket loaded active listening CUPS Printing Service Sockets [root@host-1-129 ~]# systemctl --all | grep -i cups cups.path loaded active waiting CUPS Printer Service Spool cups.service loaded inactive dead CUPS Printing Service cups.socket loaded active listening CUPS Printing Service Sockets [root@host-1-129 ~]# systemctl start cups.service [root@host-1-129 ~]# systemctl --all | grep -i cups cups.path loaded active waiting CUPS Printer Service Spool cups.service loaded active running CUPS Printing Service cups.socket loaded active running CUPS Printing Service Sockets [root@host-1-129 ~]#
6. Check status of a unit.
[root@host-1-129 ~]# systemctl status cups.service
● cups.service - CUPS Printing Service
Loaded: loaded (/usr/lib/systemd/system/cups.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2021-06-10 09:37:40 BST; 3min 40s ago
Main PID: 7459 (cupsd)
CGroup: /system.slice/cups.service
└─7459 /usr/sbin/cupsd -f
Jun 10 09:37:40 host-1-129.linuxngel.net systemd[1]: Started CUPS Printing Service.
Jun 10 09:37:40 host-1-129.linuxngel.net systemd[1]: Starting CUPS Printing Service...
[root@host-1-129 ~]#
7. Check if a unit is enabled or not.
[root@host-1-129 ~]# systemctl is-enabled cups.service enabled ### To enable the service to start on system boot # systemctl enable cups.service ### To disable a service # systemctl disable cups.service
8. To reload systemd daemon to recognize any new/remvoved unit.
[root@host-1-129 ~]# systemctl daemon-reload [root@host-1-129 ~]#