ReaR backup fails to run with CIFS

Issue

• ReaR fails to run with CIFS, e.g.

# rear -d -v mkbackup
Relax-and-Recover 2.4 / Git
Using log file: /var/log/rear/rear-rhel7u8.log
ERROR: Mount command 'mount -v -o rw,guest //<ip>/smb_bakup /tmp/rear.4fZULpaFEPwHRtP/outputfs' failed.
Aborting due to an error, check /var/log/rear/rear-rhel7u8.log for details
Exiting rear mkbackup (PID 75603) and its descendant processes
Running exit tasks
You should also rm -Rf /tmp/rear.4fZULpaFEPwHRtP
Terminated

# rear -d -v mkbackup
Relax-and-Recover 2.4 / Git
Using log file: /var/log/rear/rear-rhel7u8.log
Using backup archive '/tmp/rear.f9SAaMSnAk9DJS9/outputfs/rhel7u8/backup.tar.gz'
Creating disk layout
Using guessed bootloader 'GRUB' (found in first bytes on /dev/sda)
Creating root filesystem layout
Handling network interface 'ens33'
ens33 is a physical device
Handled network interface 'ens33'
To log into the recovery system via ssh set up /root/.ssh/authorized_keys or specify SSH_ROOT_PASSWORD
Copying logfile /var/log/rear/rear-rhel7u8.log into initramfs as '/tmp/rear-rhel7u8-partial-2022-01-18T12:37:53+0800.log'
Copying files and directories
Copying binaries and libraries
Copying kernel modules
Copying all files in /lib*/firmware/
Creating recovery/rescue system initramfs/initrd initrd.cgz with gzip default compression
Created initrd.cgz with gzip default compression (255306230 bytes) in 28 seconds
ERROR: Mount command 'mount -v -o rw,guest //<ip>/smb_bakup /tmp/rear.f9SAaMSnAk9DJS9/outputfs' failed.
Aborting due to an error, check /var/log/rear/rear-rhel7u8.log for details
Exiting rear mkbackup (PID 56531) and its descendant processes
Running exit tasks
You should also rm -Rf /tmp/rear.f9SAaMSnAk9DJS9
Terminated