Fix multipath daemon error about missing path when using VirtualBox.

Identify the issue by reading the syslog log file.

$ sudo tail -f /var/log/syslog
Jan  2 23:36:42 ubuntu-focal multipathd[524]: sdc: failed to get sysfs uid: No data available
Jan  2 23:36:42 ubuntu-focal multipathd[524]: sdc: failed to get sgio uid: No data available
Jan  2 23:36:44 ubuntu-focal multipathd[524]: sda: add missing path
Jan  2 23:36:44 ubuntu-focal multipathd[524]: sda: failed to get udev uid: Invalid argument
Jan  2 23:36:44 ubuntu-focal multipathd[524]: sda: failed to get sysfs uid: No data available
Jan  2 23:36:44 ubuntu-focal multipathd[524]: sda: failed to get sgio uid: No data available
Jan  2 23:36:45 ubuntu-focal multipathd[524]: sdd: add missing path
Jan  2 23:36:45 ubuntu-focal multipathd[524]: sdd: failed to get udev uid: Invalid argument
Jan  2 23:36:45 ubuntu-focal multipathd[524]: sdd: failed to get sysfs uid: No data available
Jan  2 23:36:45 ubuntu-focal multipathd[524]: sdd: failed to get sgio uid: No data available

It looks like multipath daemon cannot determine a unique path identifier (WWID).

List disk class of hardware.

$ sudo lshw -class disk
  *-disk:0                  
       description: SCSI Disk
       product: HARDDISK
       vendor: VBOX
       physical id: 0.0.0
       bus info: scsi@2:0.0.0
       logical name: /dev/sda
       version: 1.0
       size: 40GiB (42GB)
       capabilities: partitioned partitioned:dos
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512 signature=ce8ff640
  *-disk:1
       description: SCSI Disk
       product: HARDDISK
       vendor: VBOX
       physical id: 0.1.0
       bus info: scsi@2:0.1.0
       logical name: /dev/sdb
       version: 1.0
       size: 10MiB (10MB)
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512
  *-disk:2
       description: SCSI Disk
       product: HARDDISK
       vendor: VBOX
       physical id: 0.3.0
       bus info: scsi@2:0.3.0
       logical name: /dev/sdc
       version: 1.0
       size: 8GiB (8589MB)
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512
  *-disk:3
       description: SCSI Disk
       product: HARDDISK
       vendor: VBOX
       physical id: 0.4.0
       bus info: scsi@2:0.4.0
       logical name: /dev/sdd
       version: 1.0
       size: 8GiB (8589MB)
       configuration: ansiversion=5 logicalsectorsize=512 sectorsize=512

Blacklist these devices in multipath daemon configuration file.

$ cat <<EOF | sudo tee -a /etc/multipath.conf
blacklist {
  device {
    vendor "VBOX"
    product "HARDDISK"
  }
}
EOF

Inspect multipath daemon configuration file.

$ cat /etc/multipath.conf 
defaults {
    user_friendly_names yes
}
blacklist {
  device {
    vendor "VBOX"
    product "HARDDISK"
  }
}

Restart multipath daemon.

$ sudo systemctl restart multipathd.service

Inspect blacklist.

$ sudo multipathd show blacklist
device node rules:
- blacklist:
        (default rule)     ^(ram|zram|raw|loop|fd|md|dm-|sr|scd|st|dcssblk)[0-9]
        (default rule)     ^(td|hd|vd)[a-z]
        (default rule)     ^cciss!c[0-9]d[0-9]*
- exceptions:
        <empty>
udev property rules:
- blacklist:
        <empty>
- exceptions:
        (default rule)     (SCSI_IDENT_|ID_WWN)
protocol rules:
- blacklist:
        <empty>
- exceptions:
        <empty>
wwid rules:
- blacklist:
        <empty>
- exceptions:
        <empty>
device rules:
- blacklist:
        (config file rule) VBOX:HARDDISK
        (default rule)     SGI:Universal Xport
        (default rule)     ^DGC:LUNZ
        (default rule)     EMC:LUNZ
        (default rule)     DELL:Universal Xport
        (default rule)     IBM:Universal Xport
        (default rule)     IBM:S/390
        (default rule)     LENOVO:Universal Xport
        (default rule)     (NETAPP|LSI|ENGENIO):Universal Xport
        (default rule)     STK:Universal Xport
        (default rule)     SUN:Universal Xport
        (default rule)     (Intel|INTEL):VTrak V-LUN
        (default rule)     Promise:VTrak V-LUN
        (default rule)     Promise:Vess V-LUN
- exceptions:
        <empty>

Inspect the syslog log file.

$ sudo tail -f /var/log/syslog 
Jan  3 00:00:50 ubuntu-focal multipathd[524]: sdc: add missing path
Jan  3 00:00:50 ubuntu-focal multipathd[524]: sdc: failed to get udev uid: Invalid argument
Jan  3 00:00:50 ubuntu-focal multipathd[524]: sdc: failed to get sysfs uid: No data available
Jan  3 00:00:50 ubuntu-focal multipathd[524]: sdc: failed to get sgio uid: No data available
Jan  3 00:00:52 ubuntu-focal multipathd[524]: sda: add missing path
Jan  3 00:00:52 ubuntu-focal multipathd[524]: sda: failed to get udev uid: Invalid argument
Jan  3 00:00:52 ubuntu-focal multipathd[524]: sda: failed to get sysfs uid: No data available
Jan  3 00:00:52 ubuntu-focal multipathd[524]: sda: failed to get sgio uid: No data available
Jan  3 00:00:53 ubuntu-focal multipathd[524]: sdd: add missing path
Jan  3 00:00:53 ubuntu-focal multipathd[524]: sdd: failed to get udev uid: Invalid argument
Jan  3 00:00:53 ubuntu-focal multipathd[524]: sdd: failed to get sysfs uid: No data available
Jan  3 00:00:53 ubuntu-focal multipathd[524]: sdd: failed to get sgio uid: No data available
Jan  3 00:00:54 ubuntu-focal multipathd[524]: sdb: add missing path
Jan  3 00:00:54 ubuntu-focal multipathd[524]: sdb: failed to get udev uid: Invalid argument
Jan  3 00:00:54 ubuntu-focal multipathd[524]: sdb: failed to get sysfs uid: No data available
Jan  3 00:00:54 ubuntu-focal multipathd[524]: sdb: failed to get sgio uid: No data available
Jan  3 00:00:54 ubuntu-focal multipathd[524]: exit (signal)
Jan  3 00:00:54 ubuntu-focal multipathd[524]: --------shut down-------
Jan  3 00:00:54 ubuntu-focal systemd[1]: Stopping Device-Mapper Multipath Device Controller...
Jan  3 00:00:54 ubuntu-focal systemd[1]: multipathd.service: Succeeded.
Jan  3 00:00:54 ubuntu-focal systemd[1]: Stopped Device-Mapper Multipath Device Controller.
Jan  3 00:00:54 ubuntu-focal systemd[1]: Starting Device-Mapper Multipath Device Controller...
Jan  3 00:00:54 ubuntu-focal multipathd[9369]: --------start up--------
Jan  3 00:00:54 ubuntu-focal multipathd[9369]: read /etc/multipath.conf
Jan  3 00:00:54 ubuntu-focal multipathd[9369]: path checkers start up
Jan  3 00:00:54 ubuntu-focal systemd[1]: Started Device-Mapper Multipath Device Controller.

Alternatively, you can blacklist every sd device.

blacklist {
  devnode "^sd[a-z]"
}

In case you do not plan to use multipath, then simply remove it.

$ sudo apt remove multipath-tools