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 have the ability to dig deeper if you like. Services may start multiple processes as they run. Services tend to be the most important things to monitor on a Cumulus Linux switch.

You manage services in Cumulus Linux in the following ways:

  • Identify currently active or stopped services
  • Identify boot time state of a specific service
  • Disable or enable a specific service
  • Identify active listener ports

systemd and the systemctl Command

In general, you manage services using systemd via the systemctl command. You use it with any service on the switch to start, stop, restart, reload, enable, disable, reenable, or get the status of the service.

cumulus@switch:~$ sudo systemctl start | stop | restart | status | reload | enable | disable | reenable SERVICENAME.service

For example to restart networking, run the command:

cumulus@switch:~$ sudo systemctl restart networking.service

Unlike the service command in Debian Wheezy, the service name is written after the systemctl subcommand, not before it.

To see all the currently running services, run:

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: /
           ├─1 /sbin/init
           └─system.slice
             ├─dbus.service
             │ └─403 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
             ├─uuidd.service
             │ └─669 /usr/sbin/uuidd --socket-activation
             ├─cron.service
             │ └─381 /usr/sbin/cron -f -L 38
             ├─smond.service
             │ └─606 /usr/bin/python /usr/sbin/smond
             ├─switchd.service
             │ └─587 /usr/sbin/switchd -vx
             ├─ledmgrd.service
             │ └─613 /usr/bin/python /usr/sbin/ledmgrd
             ├─wd_keepalive.service
             │ └─433 /usr/sbin/wd_keepalive
             ├─netq-agent.service
             │ └─915 /usr/bin/python /usr/sbin/netq-agent
             ├─ptmd.service
             │ └─914 /usr/sbin/ptmd -l INFO
             ├─networking.service
             │ ├─729 /sbin/dhclient -pf /run/dhclient.vagrant.pid -lf /var/lib/dhcp/dhclient.vagrant.leases vagrant
             │ └─828 /sbin/dhclient -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases eth0
             ├─nginx.service
             │ ├─449 nginx: master process /usr/sbin/nginx -g daemon on; master_process on
             │ ├─450 nginx: worker process                           
             │ ├─451 nginx: worker process                           
             │ ├─452 nginx: worker process                           
             │ └─453 nginx: worker process                           
             ├─sysmonitor.service
             │ ├─ 847 /bin/bash /usr/lib/cumulus/sysmonitor
             │ └─7717 sleep 60
             ├─system-serial\x2dgetty.slice
             │ └─serial-getty@ttyS0.service
             │   └─920 /sbin/agetty --keep-baud 115200 38400 9600 ttyS0 vt102
             ├─neighmgrd.service
             │ └─844 /usr/bin/python /usr/bin/neighmgrd
             ├─systemd-journald.service
             │ └─252 /lib/systemd/systemd-journald
             ├─netqd.service
             │ └─846 /usr/bin/python /usr/sbin/netqd --daemon
             ├─auditd.service
             │ └─337 /sbin/auditd -n
             ├─pwmd.service
             │ └─614 /usr/bin/python /usr/sbin/pwmd
             ├─netd.service
             │ └─845 /usr/bin/python -O /usr/sbin/netd -d
             ├─ssh.service
             │ ├─ 937 /usr/sbin/sshd -D
             │ ├─6893 sshd: cumulus [priv]
             │ ├─6911 sshd: cumulus@pts/0
             │ ├─6912 -bash
             │ ├─7747 sudo systemctl status
             │ ├─7752 systemctl status
             │ └─7753 pager
             ├─systemd-logind.service
             │ └─405 /lib/systemd/systemd-logind
             ├─system-getty.slice
             │ └─getty@tty1.service
             │   └─435 /sbin/agetty --noclear tty1 linux
             ├─systemd-udevd.service
             │ └─254 /lib/systemd/systemd-udevd
             ├─mcelog.service
             │ └─438 /usr/sbin/mcelog --ignorenodev --daemon --foreground
             ├─portwd.service
             │ └─603 /usr/bin/python /usr/sbin/portwd
             ├─lldpd.service
             │ ├─911 lldpd: monitor.        
             │ └─936 lldpd: connected to oob-mgmt-switch
             ├─rsyslog.service
             │ └─392 /usr/sbin/rsyslogd -n
             ├─ntp.service
             │ └─912 /usr/sbin/ntpd -n -u ntp:ntp -g
             ├─acpid.service
             │ └─390 /usr/sbin/acpid
             └─mstpd.service
               └─436 /sbin/mstpd -d -v2

systemctl Subcommands

systemctl has a number of subcommands that perform a specific operation on a given service.

  • 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. So if there are dependent services or services that mark the restarted service as Required, the other services also get restarted. For example, running systemctl restart frr.service restarts any of the routing protocol services that are enabled and running, such as bgpd or ospfd.

  • reload: Reloads a service’s configuration.

  • 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. A disabled service can still be started or stopped.

  • reenable: Disables, then enables a service. You might need to do this so that any new Wants or WantedBy lines create the symlinks necessary for ordering. This has no side effects on other services.

There is often little reason to interact with the services directly using these commands. If a critical service should happen to crash or hit an error it will be automatically respawned by systemd. Systemd is effectively the caretaker of services in modern Linux systems and is responsible for starting all the necessary services at boot time.

Ensure a Service Starts after Multiple Restarts

By default, systemd is configured to try to restart a particular service only a certain number of times within a given interval before the service fails to start at all. The settings for this are stored in the service script. The settings are StartLimitInterval (which defaults to 10 seconds) and StartBurstLimit (which defaults to 5 attempts), but many services override these defaults, sometimes with much longer times. switchd.service, for example, sets StartLimitInterval=10m and StartBurstLimit=3, which means if you restart switchd more than 3 times in 10 minutes, it does not start.

When the restart fails for this reason, a message similar to the following appears:

Job for switchd.service failed. See 'systemctl status switchd.service' and 'journalctl -xn' for details.

And 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 any systemd service that can be started from another systemd service, you must use the --no-block option with systemctl. Otherwise, that service or even the switch itself might hang after starting or restarting.

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 Services Currently Active or Stopped

To determine which services are currently active or stopped, run the cl-service-summary command:

cumulus@switch:~$ cl-service-summary
Service cron               enabled    active   
Service ssh                enabled    active   
Service syslog             enabled    active   
Service asic-monitor       enabled    inactive
Service clagd              enabled    inactive
Service cumulus-poe                   inactive
Service lldpd              enabled    active   
Service mstpd              enabled    active   
Service neighmgrd          enabled    active   
Service netd               enabled    active   
Service netq-agent         enabled    active   
Service ntp                enabled    active   
Service portwd             enabled    active   
Service ptmd               enabled    active   
Service pwmd               enabled    active   
Service smond              enabled    active   
Service switchd            enabled    active   
Service sysmonitor         enabled    active   
Service vxrd               disabled   inactive
Service vxsnd              disabled   inactive
Service rdnbrd             disabled   inactive
Service frr                enabled    inactive
Service bgpd               disabled   inactive
Service eigrpd             disabled   inactive
Service isisd              disabled   inactive
Service ldpd               disabled   inactive
Service nhrpd              disabled   inactive
Service ospf6d             disabled   inactive
Service ospfd              disabled   inactive
Service pbrd               disabled   inactive
Service pimd               disabled   inactive
Service ripd               disabled   inactive
Service ripngd             disabled   inactive
Service zebra              disabled   inactive

You can also run the systemctl list-unit-files --type service command to list all services on the switch and see which ones are enabled:

Click here to see output of this command …

cumulus@switch:~$ systemctl list-unit-files --type service
UNIT FILE                              STATE   
aclinit.service                        enabled
acltool.service                        enabled
acpid.service                          disabled
asic-monitor.service                   enabled
auditd.service                         enabled
autovt@.service                        disabled
bmcd.service                           disabled
bootlog.service                        enabled
bootlogd.service                       masked  
bootlogs.service                       masked  
bootmisc.service                       masked  
checkfs.service                        masked  
checkroot-bootclean.service            masked  
checkroot.service                      masked  
clagd.service                          enabled
console-getty.service                  disabled
console-shell.service                  disabled
container-getty@.service               static  
cron.service                           enabled
cryptdisks-early.service               masked  
cryptdisks.service                     masked  
cumulus-aclcheck.service               static  
cumulus-chassis-ssh.service            disabled
cumulus-chassisd.service               disabled
cumulus-core.service                   static  
cumulus-fastfailover.service           enabled
cumulus-firstboot.service              disabled
cumulus-hyperconverged.service         disabled
cumulus-platform.service               enabled
cumulus-support.service                static  
dbus-org.freedesktop.hostname1.service static  
dbus-org.freedesktop.locale1.service   static  
dbus-org.freedesktop.login1.service    static  
dbus-org.freedesktop.machine1.service  static  
dbus-org.freedesktop.timedate1.service static  
dbus.service                           static  
debian-fixup.service                   static  
debug-shell.service                    disabled
decode-syseeprom.service               static  
dhcpd.service                          disabled
dhcpd6.service                         disabled
dhcpd6@.service                        disabled
dhcpd@.service                         disabled
dhcrelay.service                       disabled
dhcrelay6.service                      disabled
dhcrelay6@.service                     disabled
dhcrelay@.service                      disabled
dm-event.service                       disabled
dns-watcher.service                    disabled
dnsmasq.service                        disabled
emergency.service                      static  
frr.service                            enabled
fuse.service                           masked  
getty-static.service                   static  
getty@.service                         enabled
halt-local.service                     static  
halt.service                           masked  
heartbeat-failed@.service              static  
hostapd.service                        disabled
hostname.service                       masked  
hsflowd.service                        disabled
hsflowd@.service                       disabled
hwclock-save.service                   enabled
hwclock.service                        masked  
hwclockfirst.service                   masked  
ifup@.service                          static  
initrd-cleanup.service                 static  
initrd-parse-etc.service               static  
initrd-switch-root.service             static  
initrd-udevadm-cleanup-db.service      static  
ipmievd.service                        disabled
killprocs.service                      masked  
kmod-static-nodes.service              static  
kmod.service                           static  
ledmgrd.service                        enabled
lldpd.service                          enabled
lm-sensors.service                     enabled
lvm2-activation-early.service          enabled
lvm2-activation.service                enabled
lvm2-lvmetad.service                   static  
lvm2-monitor.service                   enabled
lvm2-pvscan@.service                   static  
lvm2.service                           disabled
mcelog.service                         enabled
module-init-tools.service              static  
motd.service                           masked  
mountall-bootclean.service             masked  
mountall.service                       masked  
mountdevsubfs.service                  masked  
mountkernfs.service                    masked  
mountnfs-bootclean.service             masked  
mountnfs.service                       masked  
mstp_bridge.service                    enabled
mstpd.service                          enabled
neighmgrd.service                      enabled
netd.service                           enabled
netq-agent.service                     enabled
netq-agent@.service                    disabled
netq-notifier.service                  disabled
netq-notifier@.service                 disabled
netqd.service                          enabled
netqd@.service                         disabled
networking.service                     enabled
nginx.service                          enabled
ntp.service                            enabled
ntp@.service                           disabled
open-vm-tools.service                  enabled
openvswitch-vtep.service               disabled
phc2sys.service                        disabled
phy-ucode-update.service               enabled
portwd.service                         enabled
procps.service                         static  
ptmd.service                           enabled
ptp4l.service                          disabled
pwmd.service                           enabled
quotaon.service                        static  
rc-local.service                       static  
rc.local.service                       static  
rdnbrd.service                         disabled
reboot.service                         masked  
rescue.service                         static  
restserver.service                     disabled
rmnologin.service                      masked  
rsyslog.service                        enabled
screen-cleanup.service                 masked  
sendsigs.service                       masked  
serial-getty@.service                  disabled
single.service                         masked  
smartd.service                         masked  
smartmontools.service                  disabled
smond.service                          enabled
snmpd.service                          disabled
snmpd@.service                         disabled
snmptrapd.service                      disabled
snmptrapd@.service                     disabled
ssh.service                            enabled
ssh@.service                           disabled
sshd.service                           enabled
stop-bootlogd-single.service           masked  
stop-bootlogd.service                  masked  
stopssh.service                        enabled
sudo.service                           disabled
switchd-diag.service                   static  
switchd.service                        enabled
syslog.service                         enabled
sysmonitor.service                     enabled
systemd-ask-password-console.service   static  
systemd-ask-password-wall.service      static  
systemd-backlight@.service             static  
systemd-binfmt.service                 static  
systemd-fsck-root.service              static  
systemd-fsck@.service                  static  
systemd-halt.service                   static  
systemd-hibernate.service              static  
systemd-hostnamed.service              static  
systemd-hybrid-sleep.service           static  
systemd-initctl.service                static  
systemd-journal-flush.service          static  
systemd-journald.service               static  
systemd-kexec.service                  static  
systemd-localed.service                static  
systemd-logind.service                 static  
systemd-machined.service               static  
systemd-modules-load.service           static  
systemd-networkd-wait-online.service   disabled
systemd-networkd.service               disabled
systemd-nspawn@.service                disabled
systemd-poweroff.service               static  
systemd-quotacheck.service             static  
systemd-random-seed.service            static  
systemd-readahead-collect.service      disabled
systemd-readahead-done.service         static  
systemd-readahead-drop.service         disabled
systemd-readahead-replay.service       disabled
systemd-reboot.service                 static  
systemd-remount-fs.service             static  
systemd-resolved.service               disabled
systemd-rfkill@.service                static  
systemd-setup-dgram-qlen.service       static  
systemd-shutdownd.service              static  
systemd-suspend.service                static  
systemd-sysctl.service                 static  
systemd-timedated.service              static  
systemd-timesyncd.service              disabled
systemd-tmpfiles-clean.service         static  
systemd-tmpfiles-setup-dev.service     static  
systemd-tmpfiles-setup.service         static  
systemd-udev-settle.service            static  
systemd-udev-trigger.service           static  
systemd-udevd.service                  static  
systemd-update-utmp-runlevel.service   static  
systemd-update-utmp.service            static  
systemd-user-sessions.service          static  
udev-finish.service                    static  
udev.service                           static  
umountfs.service                       masked  
umountnfs.service                      masked  
umountroot.service                     masked  
update-ports.service                   enabled
urandom.service                        static  
user@.service                          static  
uuidd.service                          static  
vboxadd-service.service                enabled
vboxadd-x11.service                    enabled
vboxadd.service                        enabled
vxrd.service                           disabled
vxsnd.service                          disabled
wd_keepalive.service                   enabled
x11-common.service                     masked  
ztp.service                            disabled
210 unit files listed.
lines 165-213/213 (END)

Identify Essential Services

If you need to know which services are required to run when the switch boots, run:

cumulus@switch:~$ systemctl list-dependencies --before basic.target

To see which services are needed for networking, run:

cumulus@switch:~$ systemctl list-dependencies --after network.target

├─switchd.service
├─wd_keepalive.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 Only on Mellanox switches, interfaces with the Spectrum ASIC. YES
portwd Reads pluggable information over the I2C bus. Identifies and classifies the optics that are inserted into the system. Sets interface speeds and capabilities to match the optics. YES, eventually, if optics are added/removed
frr FRRouting, handles routing protocols. There are separate processes for each routing protocol, like bgpd and ospfd. YES if routing
clag Cumulus link aggregation daemon, handles MLAG. YES if using MLAG
neighmgrd Synchronizes MAC address information when MLAG is in use. YES if using MLAG
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
netd NCLU back end. 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