Understanding DM-multipath deamon (multipathd)

The multipathd daemon checks for failed paths and reconfigures the multipath map. The daemon runs the multipath utility when events occur that require a device map reconfiguration. You can run the daemon in the foreground, which displays all messages using the -d option. You can set the verbosity level using the -v [level] option. The multipathd daemon also has an interactive mode enabled with the –k option. Some of the commands available in interactive mode include:

• help – List the available interactive commands.
• list|show paths – Show the paths that multipathd is monitoring and their state.
• list|show maps|multipaths – Show the multipath devices that multipathd is monitoring.
• list|show topology – Show the multipath topology. This gives the same output as using the multipath -ll command.
• list|show config – Show the current configuration that is derived from /etc/multipath.conf.
• reconfigure – Reconfigure the multipaths. This is triggered automatically after any hotplug event.
• quit|exit – End the interactive session.

To run the daemon in the foreground (the following example shows that the daemon is running, stops the daemon, and then starts the daemon in the foreground):

# multipathd –d
[date_time] | ux_socket_listen error 

# systemctl stop multipathd 

# multipathd –d
[date_time] | mpatha: load table [0 20971520 multipath 0 0 1 1 service-time 0 1 1 8:0 1]
[date_time] | mpatha: event checker started
[date_time] | path checkers start up

The following example runs the daemon in interactive mode:

 # multipathd –k
multipathd> help
list|show paths
list|show paths format $format ...

 multipathd> list paths
hcil     dev  dev_t  pri  dm_st   chk_st  dev_st   next_check 
2:0:0:1  sda  8:0    1    active  ready   running  .......... 1/20 
2:0:0:2  sdb  8:16   1    active  ready   running  .......... 1/20 
...

multipathd> list maps
name     sysfs   uuid
mpatha   dm-2    36001405a7c28190541f4d61880050090
mpathb   dm-3    36001405346939038cc9480caf0dd9a9d 

multipathd> list devices
available block devices:
      sda  devnode whitelisted, monitored
      sdb  devnode whitelisted, monitored
      sr0  devnode blacklisted, unmonitored
      dm-0 devnode blacklisted, unmonitored
      ...
multipathd> quit