Services and Daemons in Cumulus Linux
Services (also known as daemons) and processes are at the heart of how a Linux system functions. Most of the time, a service takes care of itself; you just enable and start it, then let it run. However, because a Cumulus Linux switch is a Linux system, you can dig deeper if you like. Services can start multiple processes as they run. Services are important to monitor on a Cumulus Linux switch.
You manage services in Cumulus Linux to identify all active or stopped services and the boot time state of a specific service, disable or enable a specific service, and identify active listener ports.
systemd and the systemctl Command
You manage services that use systemd with the systemctl command.
| Command Options | Description |
|---|---|
status | Returns the status of the specified service. |
start | Starts the service. |
stop | Stops the service. |
restart | Stops, then starts the service, all the while maintaining state. If there are dependent services or services that mark the restarted service as Required, the other services also restart. For example, running systemctl restart frr.service restarts any of the routing protocol services that you enable and that are running, such as bgpd or ospfd. |
reload | Reloads the configuration for the service. |
enable | Enables the service to start when the system boots, but does not start it unless you use the systemctl start SERVICENAME.service command or reboot the switch. |
disable | Disables the service, but does not stop it unless you use the systemctl stop SERVICENAME.service command or reboot the switch. You can start or stop a disabled service. |
reenable | Disables, then enables a service. Run this command so that any new Wants or WantedBy lines create the symlinks necessary for ordering. This does not affect on other services. |
You do not need to interact with the services directly using these commands. If a critical service crashes or encounters an error, systemd restarts it automatically. systemd is the caretaker of services in modern Linux systems and responsible for starting all the necessary services at boot time.
The following example restarts the networking service:
cumulus@switch:~$ sudo systemctl restart networking.service
The following example shows all running services:
cumulus@switch:~$ sudo systemctl status
● switch
State: running
Jobs: 0 queued
Failed: 0 units
Since: Thu 2019-01-10 00:19:34 UTC; 23h ago
CGroup: /
├─init.scope
│ └─1 /sbin/init
└─system.slice
├─haveged.service
│ └─234 /usr/sbin/haveged --Foreground --verbose=1 -w 1024
├─sysmonitor.service
│ ├─ 658 /bin/bash /usr/lib/cumulus/sysmonitor
│ └─26543 sleep 60
├─systemd-udevd.service
│ └─218 /lib/systemd/systemd-udevd
├─system-ntp.slice
│ └─ntp@mgmt.service
│ └─vrf
│ └─mgmt
│ └─12108 /usr/sbin/ntpd -n -u ntp:ntp -g
├─cron.service
│ └─274 /usr/sbin/cron -f -L 38
├─system-serial\x2dgetty.slice
│ └─serial-getty@ttyS0.service
│ └─745 /sbin/agetty -o -p -- \u --keep-baud 115200,38400,9600 ttyS0 vt220
├─nginx.service
│ ├─332 nginx: master process /usr/sbin/nginx -g daemon on; master_process on;
│ └─333 nginx: worker process
├─auditd.service
│ └─235 /sbin/auditd
├─rasdaemon.service
│ └─275 /usr/sbin/rasdaemon -f -r
├─clagd.service
│ └─11443 /usr/bin/python /usr/sbin/clagd --daemon 169.254.1.2 peerlink.4094 44:39:39:ff:40:9
--priority 100 --vxlanAnycas
├─switchd.service
│ └─430 /usr/sbin/switchd -vx
...
Add the service name after the systemctl argument.
Ensure a Service Starts after Multiple Restarts
By default, systemd tries to restart a particular service only a certain number of times within a given interval before the service fails to start. The settings StartLimitInterval (which defaults to 10 seconds) and StartBurstLimit (which defaults to 5 attempts) are in the service script; however, certain services override these defaults, sometimes with much longer times. For example, switchd.service sets StartLimitInterval=10m and StartBurstLimit=3; therefore, if you restart switchd more than three times in ten minutes, it does not start.
When the restart fails for this reason, you see a message similar to the following:
Job for switchd.service failed. See 'systemctl status switchd.service' and 'journalctl -xn' for details.
systemctl status switchd.service shows output similar to:
Active: failed (Result: start-limit) since Thu 2016-04-07 21:55:14 UTC; 15s ago
To clear this error, run systemctl reset-failed switchd.service. If you know you are going to restart frequently (multiple times within the StartLimitInterval), you can run the same command before you issue the restart request. This also applies to stop followed by start.
Keep systemd Services from Hanging after Starting
If you start, restart, or reload a systemd service that you can start from another systemd service, you must use the --no-block option with systemctl.
Identify Active Listener Ports for IPv4 and IPv6
You can identify the active listener ports under both IPv4 and IPv6 using the netstat command:
cumulus@switch:~$ netstat -nlp --inet --inet6
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:53 0.0.0.0:* LISTEN 444/dnsmasq
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 874/sshd
tcp6 0 0 :::53 :::* LISTEN 444/dnsmasq
tcp6 0 0 :::22 :::* LISTEN 874/sshd
udp 0 0 0.0.0.0:28450 0.0.0.0:* 839/dhclient
udp 0 0 0.0.0.0:53 0.0.0.0:* 444/dnsmasq
udp 0 0 0.0.0.0:68 0.0.0.0:* 839/dhclient
udp 0 0 192.168.0.42:123 0.0.0.0:* 907/ntpd
udp 0 0 127.0.0.1:123 0.0.0.0:* 907/ntpd
udp 0 0 0.0.0.0:123 0.0.0.0:* 907/ntpd
udp 0 0 0.0.0.0:4784 0.0.0.0:* 909/ptmd
udp 0 0 0.0.0.0:3784 0.0.0.0:* 909/ptmd
udp 0 0 0.0.0.0:3785 0.0.0.0:* 909/ptmd
udp6 0 0 :::58352 :::* 839/dhclient
udp6 0 0 :::53 :::* 444/dnsmasq
udp6 0 0 fe80::a200:ff:fe00::123 :::* 907/ntpd
udp6 0 0 ::1:123 :::* 907/ntpd
udp6 0 0 :::123 :::* 907/ntpd
udp6 0 0 :::4784 :::* 909/ptmd
udp6 0 0 :::3784 :::* 909/ptmd
Identify Active or Stopped Services
To see active or stopped services, run the cl-service-summary command:
cumulus@switch:~$ cl-service-summary
Service cron enabled active
Service ssh enabled active
Service rsyslog enabled active
Service asic-monitor enabled inactive
Service clagd disabled active
Service cumulus-poe inactive
Service lldpd enabled active
Service mstpd enabled active
Service neighmgrd enabled active
Service netd enabled active
Service netq-agent disabled inactive
Service ntp disabled inactive
Service portwd enabled inactive
Service ptmd enabled active
Service pwmd enabled active
Service smond enabled active
Service switchd enabled active
Service sysmonitor enabled active
Service vxrd inactive
Service vxsnd inactive
Service rdnbrd disabled inactive
Service frr enabled active
Service ntp@mgmt disabled inactive
Service ntp@ntp disabled inactive
...
You can also run the systemctl list-unit-files --type service command to list all services on the switch and to see their status:
cumulus@switch:~$ systemctl list-unit-files --type service
UNIT FILE STATE VENDOR PRESET
aclinit.service enabled enabled
acltool.service enabled enabled
acpid.service disabled enabled
air-agent@.service indirect enabled
apt-daily-upgrade.service static -
apt-daily.service static -
asic-monitor.service enabled enabled
atftpd.service generated -
auditd.service enabled enabled
autovt@.service alias -
blk-availability.service enabled enabled
bmcd.service disabled enabled
bootlog.service enabled enabled
cl-system-services.service enabled enabled
clagd.service disabled enabled
clagd_rebootNotifier.service disabled enabled
console-getty.service disabled disabled
console-setup.service enabled enabled
container-getty@.service static -
containerd.service disabled enabled
cron.service enabled enabled
cryptdisks-early.service masked enabled
cryptdisks.service masked enabled
csmgrd.service enabled enabled
cumulus-aclcheck.service static -
cumulus-cleanup-health_check.service static -
cumulus-cleanup-lttng_traces.service static -
cumulus-core.service static -
...
Identify Essential Services
To identify which services must run when the switch boots:
cumulus@switch:~$ systemctl list-dependencies --before basic.target
To identify which services you need for networking:
cumulus@switch:~$ systemctl list-dependencies --after network.target ● ├─switchd.service ● └─network-pre.target
To identify the services needed for a multi-user environment, run:
cumulus@switch:~$ systemctl list-dependencies --before multi-user.target ● ├─bootlog.service ● ├─systemd-readahead-done.service ● ├─systemd-readahead-done.timer ● ├─systemd-update-utmp-runlevel.service ● └─graphical.target ● └─systemd-update-utmp-runlevel.service
Important Services
The following table lists the most important services in Cumulus Linux.
| Service Name | Description | Affects Forwarding? |
|---|---|---|
switchd | Hardware abstraction daemon. Synchronizes the kernel with the ASIC. | YES |
sx_sdk | Interfaces with the Spectrum ASIC. Only on Spectrum switches. | YES |
frr | FRR. Handles routing protocols. There are separate processes for each routing protocol, such as bgpd and ospfd. | YES if routing |
clagd | Cumulus link aggregation daemon. Handles MLAG. | YES if using MLAG |
neighmgrd | Keeps neighbor entries refreshed, snoops on ARP and ND packets if ARP suppression is on, and refreshes VRR MAC addresses. | YES |
mstpd | Spanning tree protocol daemon. | YES if using layer 2 |
ptmd | Prescriptive Topology Manager. Verifies cabling based on LLDP output. Also sets up BFD sessions. | YES if using BFD |
nvued | Handles the NVUE object model. | NO |
rsyslog | Handles logging of syslog messages. | NO |
ntp | Network time protocol. | NO |
ledmgrd | LED manager. Reads the state of system LEDs. | NO |
sysmonitor | Watches and logs critical system load (free memory, disk, CPU). | NO |
lldpd | Handles Tx/Rx of LLDP information. | NO |
smond | Reads platform sensors and fan information from pwmd. | NO |
pwmd | Reads and sets fan speeds. | NO |