The Geek Diary

‘error opening class fc_host’ – systool Command Error on CentOS/RHEL 7 and 8

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The Problem

When running the systool command on CentOS/RHEL 7, the following error message is reported:

# systool -c fc_host -v
Error opening class fc_host

The Solution

The error occurs because the scsi_transport_fc module that is responsible for populating the contents of /sys/class/fc_host/ directory is not loaded on the system.

1. Manually load the scsi_transport_fc module then generate modules.dep and System.map files.

# modprobe scsi_transport_fc
# depmod
# lsmod | grep scsi_transport_fc
scsi_transport_fc 57344 0

2. Re-run the systool(1) command to confirm it displays expected output e.g:

# systool -c fc_host
Class = "fc_host"

Class Device = "host2"
      Device = "host2"

Class Device = "host3"
      Device = "host3"

3. Rebuild the initial RAM disk image.

a. Backup the existing initial RAM disk file for the currently running kernel version e.g.:

# cp -p /boot/initramfs-$(uname -r).img /boot/initramfs-$(uname -r).img.bak

b. Rebuild the initial RAM disk file for the currently running kernel version:

# dracut -f

NOTE: If you are running a kernel version that is different to the initial RAM disk version you are building (or if running in Linux Rescue Mode) you must specify the full kernel version/architecture e.g:

# dracut -f /boot/initramfs-5.4.17-2102.201.3.el7uek.x86_64.img 5.4.17-2102.201.3.el7uek.x86_64

4. Reboot the server. Upon reboot, the system should automatically load the scsi_transport_fc kernel module e.g.:

# lsmod | grep scsi_transport_fc
scsi_transport_fc 57344 0

5. Re-run the systool(1) command to confirm it displays expected output e.g.:

# systool -c fc_host
Class = "fc_host"

Class Device = "host2"
      Device = "host2"

Class Device = "host3"
      Device = "host3"

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