Listing unit files with systemctl

1. Query the state of all unit to verify a system startup.

#systemctl

[root@server1 /]# systemctl

UNIT LOAD ACTIVE SUB DESCRIPTION

proc-sys-fs-binfmt_misc.automount loaded active waiting Arbitrary Executable File Formats File System Automount Point

sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda-sda1.device loaded active plugged VMware_Virtual_S

sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda-sda2.device loaded active plugged VMware_Virtual_S

sys-devices-pci0000:00-0000:00:10.0-host2-target2:0:0-2:0:0:0-block-sda.device loaded active plugged VMware_Virtual_S

sys-devices-pci0000:00-0000:00:11.0-0000:02:01.0-net-eno16777736.device loaded active plugged PRO/1000 MT Single Port Adapter

sys-devices-pci0000:00-0000:00:11.0-0000:02:02.0-sound-card0.device loaded active plugged AudioPCI 64V/128 / Creative Sound Blaster CT4810

2. Query the state of only the service units.

# systemctl –type=service

[root@server1 /]# systemctl --type=service

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-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

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

3. Investigate any units which are in a failed or maintenance state. Optionally, add the –l option to show the full output.

# systemctl status rngd.service –l

[root@server1 /]# systemctl status rngd.service -l

rngd.service - Hardware RNG Entropy Gatherer Daemon

Loaded: loaded (/usr/lib/systemd/system/rngd.service; enabled)

Active: active (running) since Fri 2016-01-01 10:22:18 CET; 2 days ago

Main PID: 871 (rngd)

CGroup: /system.slice/rngd.service

└─871 /sbin/rngd -f

Jan 01 10:22:18 server1.example.com systemd[1]: Started Hardware RNG Entropy Gatherer Daemon.

Jan 01 10:22:19 server1.example.com rngd[871]: Unable to open file: /dev/tpm0

4. The status argument may also be used to determine if a particular unit is active and show if the unit is enabled to start at boot time. Alternate commands can also easily show the active and enabled states:

# systemctl is-active sshd

# systemctl is-enabled sshd

[root@server1 /]# systemctl is-active sshd

active

[root@server1 /]# systemctl is-enabled sshd

enabled

5. List the active state of all loaded units. Optionally, limit the type of unit. The –all option will add inactive units.

# sytsemctl list-units –type=service

# systemctl list-units –type=service –all

[root@server1 /]# systemctl list-units --type=service

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-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

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

[root@server1 /]# systemctl list-units --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

alsa-restore.service loaded inactive dead Restore Sound Card State

alsa-state.service loaded active running Manage Sound Card State (restore and st

alsa-store.service loaded inactive dead Store Sound Card State

6. View the enable and disable settings for all units. Optionally, limit the type of unit.

# systemctl list-unit-files –type=service

[root@server1 /]# systemctl list-unit-files --type=service

UNIT FILE STATE

abrt-ccpp.service enabled

abrt-oops.service enabled

abrt-pstoreoops.service disabled

abrt-vmcore.service enabled

abrt-xorg.service enabled

abrtd.service enabled

accounts-daemon.service enabled

alsa-restore.service static

alsa-state.service static

alsa-store.service static

arp-ethers.service disabled

7. View only failed services

# systemctl –failed –type=service

[root@server1 /]# systemctl --failed --type=service

UNIT LOAD ACTIVE SUB DESCRIPTION

rhnsd.service loaded failed failed LSB: Starts the Spacewalk Daemon

Starting and stopping system daemons on a running system.

1. View the status of a service.

# systemctl status

2. Verify that the process is running.

# ps –up PID

3. Stop the service and verify the status

# systemctl stop sshd.service

# systemctl status sshd.service

[root@server1 /]# systemctl stop sshd.service

[root@server1 /]# systemctl status sshd.service

sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)

Active: inactive (dead) since Mon 2016-01-04 04:44:49 CET; 11s ago

Process: 1582 ExecStart=/usr/sbin/sshd -D $OPTIONS (code=exited, status=0/SUCCESS)

Process: 1573 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS)

Main PID: 1582 (code=exited, status=0/SUCCESS)

Jan 01 10:22:47 server1.example.com systemd[1]: Started OpenSSH server daemon.

Jan 01 10:22:49 server1.example.com sshd[1582]: Server listening on 0.0.0.0 port 2022.

Jan 01 10:22:49 server1.example.com sshd[1582]: Server listening on :: port 2022.

Jan 04 04:44:49 server1.example.com systemd[1]: Stopping OpenSSH server daemon...

Jan 04 04:44:49 server1.example.com sshd[1582]: Received signal 15; terminating.

Jan 04 04:44:49 server1.example.com systemd[1]: Stopped OpenSSH server daemon.

4. Start the service and view the status. The process ID has changed

# systemctl start sshd.service

# systemctl status sshd.service

[root@server1 /]# systemctl start sshd.service

[root@server1 /]# systemctl status sshd.service

sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)

Active: active (running) since Mon 2016-01-04 04:47:56 CET; 4s ago

Process: 15722 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS)

Main PID: 15724 (sshd)

CGroup: /system.slice/sshd.service

└─15724 /usr/sbin/sshd -D

Jan 04 04:47:56 server1.example.com systemd[1]: Starting OpenSSH server daemon...

Jan 04 04:47:56 server1.example.com systemd[1]: Started OpenSSH server daemon.

Jan 04 04:47:56 server1.example.com sshd[15724]: Server listening on 0.0.0.0 port 2022.

Jan 04 04:47:56 server1.example.com sshd[15724]: Server listening on :: port 2022.

5. Stop, then start, the service in a single command.

# systemctl restart sshd.service

# systemctl status sshd.service

[root@server1 /]# systemctl restart sshd.service

[root@server1 /]# systemctl status sshd.service

sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)

Active: active (running) since Mon 2016-01-04 04:48:49 CET; 2s ago

Process: 15738 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS)

Main PID: 15739 (sshd)

CGroup: /system.slice/sshd.service

└─15739 /usr/sbin/sshd -D

Jan 04 04:48:49 server1.example.com systemd[1]: Starting OpenSSH server daemon...

Jan 04 04:48:49 server1.example.com systemd[1]: Started OpenSSH server daemon.

Jan 04 04:48:49 server1.example.com sshd[15739]: Server listening on 0.0.0.0 port 2022.

Jan 04 04:48:49 server1.example.com sshd[15739]: Server listening on :: port 2022.

6. Issue instructions for a service to read and reload its configuration file without a complete stop and start. The process ID will not change.

# systemctl reload sshd.service

# systemcl status sshd.service

[root@server1 /]# systemctl reload sshd.service

[root@server1 /]# systemctl status sshd.service

sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)

Active: active (running) since Mon 2016-01-04 04:48:49 CET; 57s ago

Process: 15754 ExecReload=/bin/kill -HUP $MAINPID (code=exited, status=0/SUCCESS)

Process: 15738 ExecStartPre=/usr/sbin/sshd-keygen (code=exited, status=0/SUCCESS)

Main PID: 15739 (sshd)

CGroup: /system.slice/sshd.service

└─15739 /usr/sbin/sshd -D

Jan 04 04:48:49 server1.example.com systemd[1]: Starting OpenSSH server daemon...

Jan 04 04:48:49 server1.example.com systemd[1]: Started OpenSSH server daemon.

Jan 04 04:48:49 server1.example.com sshd[15739]: Server listening on 0.0.0.0 port 2022.

Jan 04 04:48:49 server1.example.com sshd[15739]: Server listening on :: port 2022.

Jan 04 04:49:38 server1.example.com systemd[1]: Reloading OpenSSH server daemon.

Jan 04 04:49:38 server1.example.com sshd[15739]: Received SIGHUP; restarting.

Jan 04 04:49:38 server1.example.com sshd[15739]: Server listening on 0.0.0.0 port 2022.

Jan 04 04:49:38 server1.example.com sshd[15739]: Server listening on :: port 2022.

Jan 04 04:49:38 server1.example.com systemd[1]: Reloaded OpenSSH server daemon.

Masking services

At times, a system may have conflicting services installed. For example, there are multiple methods to manage networks (network and NetworkManager) and firewalls (iptables and firewalld). To prevent and administrator from accidentally starting a service, that service may be masked. Masking will create a link in the configuration directories so that if the service is started nothing will happen.

# systemctl mask network

# systemctl unmask network

[root@server1 /]# systemctl mask network

ln -s '/dev/null' '/etc/systemd/system/network.service'

[root@server1 /]# systemctl unmask network

rm '/etc/systemd/system/network.service'

Enabling system daemons to start or stop at boot

Starting a service on a running system does nto guarantee that the service will be started when the system reboots. Similarly, stopping a service on a running system will not keep it from starting again when the system reboots. Services are started at boot time when links are created in the appropriated systemd configuration directories. These links are created and removed with systemctl commands.

1. View the status of a service.

# systemctl status sshd.service

[root@server1 /]# systemctl status sshd.service

sshd.service - OpenSSH server daemon

Loaded: loaded (/usr/lib/systemd/system/sshd.service; enabled)

Active: active (running) since Mon 2016-01-04 04:48:49 CET; 2min 50s ago